Lawn tractor conversion: lessons learned

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Lawn tractor conversion: lessons learned

Electric Vehicle Discussion List mailing list
I got lots of useful help here on my lawn tractor conversion project —
http://www.evalbum.com/4841 — so I thought I'd post some lessons
learned, both positive and negative. None of this is intended as
advice for anyone else, for obvious reasons. I'm not doing everything
as safely as I might! This is just the "brain dump" I wish someone
else had written for me to read when I was getting started.

Biting the bullet and buying real batteries (Deka Intimidator 9A31)
was a good idea. Mowing my half-acre lot that's not much more than
half lawn sometimes brings me close to 50% DoD, occasionally perhaps
very slightly below. It took a bit of convincing myself to spend $1K
on batteries—almost twice what I spent on the Motenergy ME1004 motor.
Part of what got in the way of accepting that reality early on was a
silly idea that I could fit everything under the existing hood and it
would look the same, just be quieter. Things got a lot easier when I
decided to ditch the "hood" and embrace as part of the conversion the
fact that this was going to look way different when I was done. If I
were starting over today, I'd seriously consider getting together with
friends on breaking a scavenged Volt battery and doing a 2p15s or
3p15s arrangement (I don't recall the capacity of the volt cells).
Scavenged Volt batteries seem to be going for around $2K so if enough
people wanted to get together on it, this would have been an
opportunity to get more capacity for less money. I hope that by the
time my current batteries are going downhill, lithium cells are a dime
a dozen.

Installing muffin fans pulling cooling air through a reticulated foam
filter (like they use for aquariums) to provide positive pressure
cleaned air in a plenum around the motor was a good idea. The motor
stays clean. I don't know if it matters for cooling, since I'm running
the motor well under rated load. But cleaned air can't hurt brush
life. I count that as worth the 1.2A continuous draw. Using plexiglass
to make that plenum was a great idea. Using 1/8" plexiglas for the
sides and 1/4" only for the top where the muffin fans were mounted was
a false economy; if I were doing it again I would make the whole
plenum out of the more expensive, but more robust and easier to work
1/4" plexiglass. Given the frame I had to build to support the 1/8"
plexiglass, I think that it would have taken me less than half the
time if I'd done it all in 1/4" plexiglass. However, using a sectional
picture frame (the kind where you purchase two packages to make one
frame, one package for each dimension) as the holder for the
reticulated foam worked quite well. I'd do the same thing again even
if I weren't so incredibly lucky as to find the frame packages on sale
for 95% off... I used a combination of glue and brass screws to hold
the plexiglass together; if I were doing it again I'd just use the
brass screws. They look pretty cool in the plexiglass box if I do say
so myself.

Talking myself into doubling my 4awg welding cable for the equivalent
cross sectional area of 1awg was almost certainly overkill. Joe
Lorenzi has 8awg in his JD with the same motor, and he told me that it
gets a little warm and thicker than 8awg would be useful, but I really
don't think I need 1awg equivalent. Even immediately after mowing
through thick grass with no breaks for nearly half an hour (down to
50%DoD) my cables are cold. If I were doing it over, I would just use
the 4awg cable. Would be easier and use lighter, easier-to-manage
lugs, and routing would be less of a challenge than it was.

I bought both 400A and 200A fuses, not sure whether it would blow the
200A fuse. I needn't have worried. I do see over 100A continuous, but
the 200A fuse hasn't blown. The batteries just can't push that much
current through that motor...

Hooking up my power switch so that the charging cable is connected in
one direction, and the contactor in the other, means that I can't
accidentally try to charge it and run it at the same time, and makes
it less likely that I'll drive away and leave the charger connected.
Buying SB50 anderson connectors for charging at 48V 6A max was silly;
the charger came with C15 (just like in the back of your computer)
which works fine. So I have some unused SB50 anderson connectors...

I was originally going to connect both sides of the motor through an
SB350 anderson connector for a disconnect. Instead, I put a single
pole PP disconnect (using exactly the same internals as the SB350)
inline next to the fuse as my emergency disconnect / safety
maintenance disconnect. Requires only half the effort to pull it open
in an emergency, and the loop of wire that doubles as the emergency
disconnect handle is also convenient for my clamp ammeter! So I also
have some unused SB350 anderson connectors...

I wanted to avoid a 12V house battery and run everything off of 48V
due to my initial expectation to install one of my batteries under the
seat, before I settled on the 9A31 batteries that couldn't possibly
fit. After deciding on batteries, I didn't go back and reconsider my
design. Because of that, it was hard to source the muffin fans (found
surplus fan FRU for rack-mounted hardware), and the contactor solenoid
draws more power than it otherwise would. And now I need 12V house
power anyway if only because the amphour meter I purchased requires
isolated 12V power, so I intend to put the original starting battery
back in the empty hole under the seat and use it for house power, and
regret that it's not running my fans and contactor since they are 48V
units. It also got in the way of taking Lee Hart's excellent advice
for using two contactors to reduce the power draw. And it also kept me
from hooking up the safety interlocks — which it turns out would be
more of a pain than I expected for other reasons, so even when I add
the house battery I'm not sure I'll get the safety interlocks
connected. I do keep that in mind when using it, though. I did spend
my early childhood (as soon as I could physically reach the pedals)
driving around a couple of simplicity tractors with no interlocks...

The MTD transmatic belt-and-pully variable transmission isn't as bad
as I thought (it's not hydrostatic and by most reports it's more
efficient than a hydrostatic), but it's really imperative to get the
MTD belts and not belts advertised as "OEM replacement". The non-MTD
belts were both unsafe (the tractor wouldn't come to a complete stop)
and were so sticky that they cost me something like 20A. Also, using
them damaged the transmission a bit and made it harder to shift,
though that's gotten better since I replaced them with the MTD belts.

I was surprised to find that the bearings in the mower deck were free
and turned easily; I had expected to have to refurbish them but did
not have to do so in the end. I did replace the mower blades.

Having two of the batteries cantilevered over the front tires requires
excessive tire pressure and makes steering a lot of work. There is way
more weight forward than in the ICE configuration. I expect to replace
the steering pinion every few years; the first one lasted about 7
years but this is much heavier service. Having the other two batteries
between the console and the seat such that I have to straddle them
while I drive works, but it doesn't put enough weight at the back, so
I sometimes have to shift my weight to the back of the tractor to keep
the rear tires from spinning. The advice to instead mount them
cantilevered off the back of the tractor was good; I didn't do it
because it would get in the way of bagging. I normally mulch, but I
bag when I mow leaves in the fall. So I don't think I personally would
change that, but for anyone else considering this, if you don't need
to bag, I'd strongly suggest considering mounting rear batteries
behind the seat for better traction and balance. Better still would be
lighter batteries, like the broken Volt battery idea, or other lithium
ion, that can source the current and won't be hurt by much deeper
discharge. Would have taken a different charger, of course.

Mounting a wood bumper in front of the front batteries to protect them
was a good idea. Especially when I had the non-MTD belts installed
that didn't come to a complete stop. That protected those expensive
AGM batteries!

I definitely expect to have to sharpen the blades often; they will
draw more current if they are dull. If I remove the batteries, I can
easily and safely tip the tractor on its side to sharpen the blades.
I'd like to be very clear that this isn't advice or a recommendation.
But in doing that I know for sure that the motor can't start while I'm
trying to sharpen the blades! ☺

I did use a DPDT on-off-on switch to connect positive pole to either
the contactor or the charger, and I routed through both poles in
series so that each half sees 24V for less arcing in the switch for
longer life. I have not yet built a snubber, though on an oscilloscope
I measured a 1ms -100V pulse from the contactor solenoid. Basically,
that means that I got a 1ms -100V pulse with a 10MOhm 15pF RC snubber.
☺ I finally got an assortment of rectifier diodes and high voltage
polypropylene capacitors so I can cook up a RCD snubber to put on the
contactor solenoid thanks to Lee's excellent page on the
characteristics of various types of snubbers. No need to snub the
permanent magnet DC motor; I couldn't measure any back-EMF from it and
I have a vague sense that's typical due to the permittivity of
permanent magnets.

I'm considering making a simple PWM motor controller for the fans
since I think they are probably way overkill and I could reduce the
1.2A draw. But first I need the snubber to keep the power cleaner. One
I have that, I have a HV buck converter to supply the control circuit,
and it just takes a 555 timer, resistor, potentiometer, a few
capacitors, a few diodes, and a MOSFET to reduce the power draw from
the fans. But there's really no need. That would be just for fun.

I have not built the battery balancers. The batteries are all within
.02V of each other so far. The one balancer I built was a pain to
build. I can't figure out how Lee manages to solder the diodes to the
lugs without overheating the diodes. I had already ordered the parts
from mouser before I saw that Lee was selling them, at which point I
thought I'd just build them, and then I discovered what a pain that is
and gave up after building one that I don't really trust because the
zeners got so hot while I was soldering them into the lugs, despite my
best efforts. So if my batteries start getting out of balance, I think
I'll just cut my losses and buy a set from Lee who knows what he's
doing. I'll just add the zeners etc. to my kit of random electronics
parts and someday find a use for them.

Oh, and it seems like everyone I talk to about my project exclaims
about how cool it is that I can mow my lawn silently. Maybe they are
remembering how a Leaf or Prius or (if they are lucky) a Tesla can
sneak up on them. My motor running alone on the bench was
uncomfortably loud and I wore ear plugs for comfort when I was
breaking in the brushes while it was on the bench in the workshop.
Before the conversion, the ICE was louder than the mower deck but the
mower deck made the tractor much louder when it was engaged. Now, the
mower deck is much louder than the motor. I still wear ear plugs while
I mow the lawn.

But still, with all the mistakes and downsides and things I'd do
differently next time, I still get the EV grin while using it, which
is impressive since I really really hate to mow the lawn. Making me
happy while I mow the lawn is a definite accomplishment.
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Re: Lawn tractor conversion: lessons learned

Electric Vehicle Discussion List mailing list
RE. connecting the small diodes to large connectors, I have two solutions,
easiest is drill a small hole for a tine (#4) screw and put a ring lug on
the diode by crimping or soldering or both then screw the ring on with the
small screw to the larger connection.  Alternatively I drill a 0.033 inch
hole in copper or lead  part of the connection then clean the diode lead
off and place it into the hole which needs to be 1/4 inch deep, then prick
beside the wire and hole with a small punch which crimps the wire right
into the hole permanently...

Dennis Lee Miles

(*[hidden email] <[hidden email]>)*

* Founder:    **EV Tech. Institute Inc.*

*Phone #* *(863) 944-9913 (12 noon to 12 midnight Eastern US Time)*

*Educating yourself, does not mean you were **stupid; it means, you are
intelligent enough,  **to know, that there is plenty left to learn!*

*          You Tube Video link:  http://youtu.be/T-FVjMRVLss
<http://youtu.be/T-FVjMRVLss> *


On Mon, Jul 28, 2014 at 10:59 PM, Michael K Johnson via EV <
[hidden email]> wrote:

> I got lots of useful help here on my lawn tractor conversion project —
> http://www.evalbum.com/4841 — so I thought I'd post some lessons
> learned, both positive and negative. None of this is intended as
> advice for anyone else, for obvious reasons. I'm not doing everything
> as safely as I might! This is just the "brain dump" I wish someone
> else had written for me to read when I was getting started.
>
> Biting the bullet and buying real batteries (Deka Intimidator 9A31)
> was a good idea. Mowing my half-acre lot that's not much more than
> half lawn sometimes brings me close to 50% DoD, occasionally perhaps
> very slightly below. It took a bit of convincing myself to spend $1K
> on batteries—almost twice what I spent on the Motenergy ME1004 motor.
> Part of what got in the way of accepting that reality early on was a
> silly idea that I could fit everything under the existing hood and it
> would look the same, just be quieter. Things got a lot easier when I
> decided to ditch the "hood" and embrace as part of the conversion the
> fact that this was going to look way different when I was done. If I
> were starting over today, I'd seriously consider getting together with
> friends on breaking a scavenged Volt battery and doing a 2p15s or
> 3p15s arrangement (I don't recall the capacity of the volt cells).
> Scavenged Volt batteries seem to be going for around $2K so if enough
> people wanted to get together on it, this would have been an
> opportunity to get more capacity for less money. I hope that by the
> time my current batteries are going downhill, lithium cells are a dime
> a dozen.
>
> Installing muffin fans pulling cooling air through a reticulated foam
> filter (like they use for aquariums) to provide positive pressure
> cleaned air in a plenum around the motor was a good idea. The motor
> stays clean. I don't know if it matters for cooling, since I'm running
> the motor well under rated load. But cleaned air can't hurt brush
> life. I count that as worth the 1.2A continuous draw. Using plexiglass
> to make that plenum was a great idea. Using 1/8" plexiglas for the
> sides and 1/4" only for the top where the muffin fans were mounted was
> a false economy; if I were doing it again I would make the whole
> plenum out of the more expensive, but more robust and easier to work
> 1/4" plexiglass. Given the frame I had to build to support the 1/8"
> plexiglass, I think that it would have taken me less than half the
> time if I'd done it all in 1/4" plexiglass. However, using a sectional
> picture frame (the kind where you purchase two packages to make one
> frame, one package for each dimension) as the holder for the
> reticulated foam worked quite well. I'd do the same thing again even
> if I weren't so incredibly lucky as to find the frame packages on sale
> for 95% off... I used a combination of glue and brass screws to hold
> the plexiglass together; if I were doing it again I'd just use the
> brass screws. They look pretty cool in the plexiglass box if I do say
> so myself.
>
> Talking myself into doubling my 4awg welding cable for the equivalent
> cross sectional area of 1awg was almost certainly overkill. Joe
> Lorenzi has 8awg in his JD with the same motor, and he told me that it
> gets a little warm and thicker than 8awg would be useful, but I really
> don't think I need 1awg equivalent. Even immediately after mowing
> through thick grass with no breaks for nearly half an hour (down to
> 50%DoD) my cables are cold. If I were doing it over, I would just use
> the 4awg cable. Would be easier and use lighter, easier-to-manage
> lugs, and routing would be less of a challenge than it was.
>
> I bought both 400A and 200A fuses, not sure whether it would blow the
> 200A fuse. I needn't have worried. I do see over 100A continuous, but
> the 200A fuse hasn't blown. The batteries just can't push that much
> current through that motor...
>
> Hooking up my power switch so that the charging cable is connected in
> one direction, and the contactor in the other, means that I can't
> accidentally try to charge it and run it at the same time, and makes
> it less likely that I'll drive away and leave the charger connected.
> Buying SB50 anderson connectors for charging at 48V 6A max was silly;
> the charger came with C15 (just like in the back of your computer)
> which works fine. So I have some unused SB50 anderson connectors...
>
> I was originally going to connect both sides of the motor through an
> SB350 anderson connector for a disconnect. Instead, I put a single
> pole PP disconnect (using exactly the same internals as the SB350)
> inline next to the fuse as my emergency disconnect / safety
> maintenance disconnect. Requires only half the effort to pull it open
> in an emergency, and the loop of wire that doubles as the emergency
> disconnect handle is also convenient for my clamp ammeter! So I also
> have some unused SB350 anderson connectors...
>
> I wanted to avoid a 12V house battery and run everything off of 48V
> due to my initial expectation to install one of my batteries under the
> seat, before I settled on the 9A31 batteries that couldn't possibly
> fit. After deciding on batteries, I didn't go back and reconsider my
> design. Because of that, it was hard to source the muffin fans (found
> surplus fan FRU for rack-mounted hardware), and the contactor solenoid
> draws more power than it otherwise would. And now I need 12V house
> power anyway if only because the amphour meter I purchased requires
> isolated 12V power, so I intend to put the original starting battery
> back in the empty hole under the seat and use it for house power, and
> regret that it's not running my fans and contactor since they are 48V
> units. It also got in the way of taking Lee Hart's excellent advice
> for using two contactors to reduce the power draw. And it also kept me
> from hooking up the safety interlocks — which it turns out would be
> more of a pain than I expected for other reasons, so even when I add
> the house battery I'm not sure I'll get the safety interlocks
> connected. I do keep that in mind when using it, though. I did spend
> my early childhood (as soon as I could physically reach the pedals)
> driving around a couple of simplicity tractors with no interlocks...
>
> The MTD transmatic belt-and-pully variable transmission isn't as bad
> as I thought (it's not hydrostatic and by most reports it's more
> efficient than a hydrostatic), but it's really imperative to get the
> MTD belts and not belts advertised as "OEM replacement". The non-MTD
> belts were both unsafe (the tractor wouldn't come to a complete stop)
> and were so sticky that they cost me something like 20A. Also, using
> them damaged the transmission a bit and made it harder to shift,
> though that's gotten better since I replaced them with the MTD belts.
>
> I was surprised to find that the bearings in the mower deck were free
> and turned easily; I had expected to have to refurbish them but did
> not have to do so in the end. I did replace the mower blades.
>
> Having two of the batteries cantilevered over the front tires requires
> excessive tire pressure and makes steering a lot of work. There is way
> more weight forward than in the ICE configuration. I expect to replace
> the steering pinion every few years; the first one lasted about 7
> years but this is much heavier service. Having the other two batteries
> between the console and the seat such that I have to straddle them
> while I drive works, but it doesn't put enough weight at the back, so
> I sometimes have to shift my weight to the back of the tractor to keep
> the rear tires from spinning. The advice to instead mount them
> cantilevered off the back of the tractor was good; I didn't do it
> because it would get in the way of bagging. I normally mulch, but I
> bag when I mow leaves in the fall. So I don't think I personally would
> change that, but for anyone else considering this, if you don't need
> to bag, I'd strongly suggest considering mounting rear batteries
> behind the seat for better traction and balance. Better still would be
> lighter batteries, like the broken Volt battery idea, or other lithium
> ion, that can source the current and won't be hurt by much deeper
> discharge. Would have taken a different charger, of course.
>
> Mounting a wood bumper in front of the front batteries to protect them
> was a good idea. Especially when I had the non-MTD belts installed
> that didn't come to a complete stop. That protected those expensive
> AGM batteries!
>
> I definitely expect to have to sharpen the blades often; they will
> draw more current if they are dull. If I remove the batteries, I can
> easily and safely tip the tractor on its side to sharpen the blades.
> I'd like to be very clear that this isn't advice or a recommendation.
> But in doing that I know for sure that the motor can't start while I'm
> trying to sharpen the blades! ☺
>
> I did use a DPDT on-off-on switch to connect positive pole to either
> the contactor or the charger, and I routed through both poles in
> series so that each half sees 24V for less arcing in the switch for
> longer life. I have not yet built a snubber, though on an oscilloscope
> I measured a 1ms -100V pulse from the contactor solenoid. Basically,
> that means that I got a 1ms -100V pulse with a 10MOhm 15pF RC snubber.
> ☺ I finally got an assortment of rectifier diodes and high voltage
> polypropylene capacitors so I can cook up a RCD snubber to put on the
> contactor solenoid thanks to Lee's excellent page on the
> characteristics of various types of snubbers. No need to snub the
> permanent magnet DC motor; I couldn't measure any back-EMF from it and
> I have a vague sense that's typical due to the permittivity of
> permanent magnets.
>
> I'm considering making a simple PWM motor controller for the fans
> since I think they are probably way overkill and I could reduce the
> 1.2A draw. But first I need the snubber to keep the power cleaner. One
> I have that, I have a HV buck converter to supply the control circuit,
> and it just takes a 555 timer, resistor, potentiometer, a few
> capacitors, a few diodes, and a MOSFET to reduce the power draw from
> the fans. But there's really no need. That would be just for fun.
>
> I have not built the battery balancers. The batteries are all within
> .02V of each other so far. The one balancer I built was a pain to
> build. I can't figure out how Lee manages to solder the diodes to the
> lugs without overheating the diodes. I had already ordered the parts
> from mouser before I saw that Lee was selling them, at which point I
> thought I'd just build them, and then I discovered what a pain that is
> and gave up after building one that I don't really trust because the
> zeners got so hot while I was soldering them into the lugs, despite my
> best efforts. So if my batteries start getting out of balance, I think
> I'll just cut my losses and buy a set from Lee who knows what he's
> doing. I'll just add the zeners etc. to my kit of random electronics
> parts and someday find a use for them.
>
> Oh, and it seems like everyone I talk to about my project exclaims
> about how cool it is that I can mow my lawn silently. Maybe they are
> remembering how a Leaf or Prius or (if they are lucky) a Tesla can
> sneak up on them. My motor running alone on the bench was
> uncomfortably loud and I wore ear plugs for comfort when I was
> breaking in the brushes while it was on the bench in the workshop.
> Before the conversion, the ICE was louder than the mower deck but the
> mower deck made the tractor much louder when it was engaged. Now, the
> mower deck is much louder than the motor. I still wear ear plugs while
> I mow the lawn.
>
> But still, with all the mistakes and downsides and things I'd do
> differently next time, I still get the EV grin while using it, which
> is impressive since I really really hate to mow the lawn. Making me
> happy while I mow the lawn is a definite accomplishment.
> _______________________________________________
> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> http://lists.evdl.org/listinfo.cgi/ev-evdl.org
> For EV drag racing discussion, please use NEDRA (
> http://groups.yahoo.com/group/NEDRA)
>
>
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Re: Lawn tractor conversion: lessons learned

Electric Vehicle Discussion List mailing list
In reply to this post by Electric Vehicle Discussion List mailing list
Michael K Johnson via EV wrote:
> I got lots of useful help here on my lawn tractor conversion project —

Glad we could be of help. Congratulations on getting the "EV grin" while
mowing the lawn! :-)

> silly idea that I could fit everything under the existing hood and it
> would look the same, just be quieter.

Yeah, the batteries certainly add bulk, and there's no place to put it.
Skimp on the batteries, and they die young. I helped convert a Wheel
Horse tractor. We first tried two 12v, because they fit under the hood.
Mowing time was too short, and they only lasted one season. We crowded
in three; that got the job done, but barely. Four would have been the charm.

> I'd seriously consider getting together with friends on a scavenged
> Volt battery...

That could be fun as an experiment, but could cost more and require more
finesse to get it all to work. Dumb old lead-acids are easier, and a
reasonable first-EV solution.

> Installing muffin fans pulling cooling air through a reticulated foam
> filter (like they use for aquariums) to provide positive pressure
> cleaned air in a plenum around the motor was a good idea. The motor
> stays clean.

Putting the motor in a pressurized box is an interesting solution. The
foam filters apparently have a low enough pressure drop to work with
propeller-type fans. The more common approach uses a squirrel-cage
blower with a higher-drop filter element.

> Using plexiglass to make that plenum was a great idea.

Is it "real" plexiglass (brittle acrylic), or the more common
polycarbonate (slightly flexible, nearly unbreakable)? Polycarbonate is
so strong that even 1/8" would be indestructible.

> Talking myself into doubling my 4awg welding cable for the equivalent
> cross sectional area of 1awg was almost certainly overkill.

Well, it's a small matter. Your wire lengths are short, so not a lot of
loss no matter how you do it. What ulitmately matters is that the wire
doesn't get hot, and you've certainly achieved that.

> Hooking up my power switch so that the charging cable is connected in
> one direction, and the contactor in the other, means that I can't
> accidentally try to charge it and run it at the same time

A good plan.

> Buying SB50 anderson connectors for charging at 48V 6A max was silly;

But, they are very robust and will last. They can carry 6a even when
dirty, worn, and corroded. Maybe you'll get a higher current charger
someday. (Your AGMs might like higher-current charging anyway).

> I wanted to avoid a 12V house battery and run everything off of 48V

48v input to 12v output DC/DC converters are pretty common; the Telco
industry used them in quantity. You can probably find one surplus for
$10-$20 that can run fans, contactor coils, and your amphour meter.

> it was hard to source the muffin fans

Another trick: Industrial EVs will wire lights, fans, etc. in series to
allow use of 12v or 24v devices on 48v.

> and the contactor solenoid draws more power than it otherwise would.

If that's a worry, 48v contactor coils are very common.

> The MTD transmatic belt-and-pully variable transmission isn't as bad
> as I thought (it's not hydrostatic and by most reports it's more
> efficient than a hydrostatic), but it's really imperative to get the
> MTD belts and not belts advertised as "OEM replacement".

On snowmobiles and other users of this variable-pulley-size method, they
sometimes use metal belts (chains) with little friction pads on the
sides. They are more efficient than the typical rubber v-belts. Maybe
one is available for the size needed here?

> Having two of the batteries cantilevered over the front tires requires
> excessive tire pressure and makes steering a lot of work.

> The advice to instead mount them cantilevered off the back of the
> tractor was good; I didn't do it because it would get in the way
> of bagging.

Maybe the bagger can be moved back a bit? Or add wheel weights, or a
counterbalance weight somewhere behind the rear axle?

My ElecTraks have half the batteries in front, and the other half under
the seat. Steering is still heavier than a normal tractor, but not too bad.

> I definitely expect to have to sharpen the blades often; they will
> draw more current if they are dull.

With EVs, an ammeter makes it easy to *tell* when it's using more power.
With an ICE, there's no way to tell it's burning more gas.

> longer life. I have not yet built a snubber, though on an oscilloscope
> I measured a 1ms -100V pulse from the contactor solenoid. Basically,
> that means that I got a 1ms -100V pulse with a 10MOhm 15pF RC snubber.
> ☺ I finally got an assortment of rectifier diodes and high voltage
> polypropylene capacitors so I can cook up a RCD snubber to put on the
> contactor solenoid thanks to Lee's excellent page on the
> characteristics of various types of snubbers.

Glad it helped! An oscilloscope is the perfect way to pick the snubber
parts. You can easily see when you have good values. Add capacitance
until the peak voltage is reasonable, then add resistance until the
ringing is just about gone.

> no need to snub the permanent magnet DC motor; I couldn't measure
> any back-EMF from it and I have a vague sense that's typical due to
> the permittivity of permanent magnets.

PM motors have less inductance, so less trouble with voltage spikes.
Perversely, the lack of inductance makes them harder to use with PWM
controllesr that depend on motor inductance for the current limit to work.

> I'm considering making a simple PWM motor controller for the fans

For this to work, they have to be simple motors -- not brushless DC
motors with electronics. Almost all small fan motors are now brushless DC.

To use a PWM controller with a brushless DC fan, you'll have to add your
own series inductor and filter capacitor on the PWM output (a proper
buck converter) so you get smooth filtered DC out.

> I have not built the battery balancers. The batteries are all within
> .02V of each other so far.

That's good. Worry about balancing when they start to drift apart.

> The one balancer I built was a pain to build. I can't figure out
> how Lee manages to solder the diodes to the lugs without overheating
> the diodes.

I fold the diode lead back along the body. Insert the diode into the lug
(the folded lead holds it in place). I solder the end of the lead wire
to the inside of the lug with a BIG soldering iron, which can heat the
lug up quickly. Add solder to solder the wire to the inside of the lug.
It then cools quickly, because only that one small area of the lug was
heated to soldering temperature.

> My motor running alone on the bench was uncomfortably loud

That's surprising. It should have sounded like a vacuum cleaner motor;
not particularly loud, but perhaps annoying because there's a
whistle-like pitch to it.

> Now, the mower deck is much louder than the motor.

Isn't that always the case? :-) When we convert our ICEs to EVs, we no
longer have the ICE noise. But then we notice all the other whines,
whirrs, squeaks, thumps, and rattles that the ICE was covering up!

--
The definition of research: Shoot the arrow first, and paint the target
around where it lands. -- David Van Baak
--
Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm
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Re: Lawn tractor conversion: lessons learned

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I don't know if this has been shown here already, but a former classmate
and her husband have this company, and it is a very interesting site to
look at. They also have a FaceBook page: http://www.aclectrictractors.com/



If we cannot afford to take care of Veterans, then we should stop making
them.
David C. Wilker Jr.
USAF (RET)


On Mon, Jul 28, 2014 at 7:59 PM, Michael K Johnson via EV <[hidden email]
> wrote:

> I got lots of useful help here on my lawn tractor conversion project —
> http://www.evalbum.com/4841 — so I thought I'd post some lessons
> learned, both positive and negative. None of this is intended as
> advice for anyone else, for obvious reasons. I'm not doing everything
> as safely as I might! This is just the "brain dump" I wish someone
> else had written for me to read when I was getting started.
>
> Biting the bullet and buying real batteries (Deka Intimidator 9A31)
> was a good idea. Mowing my half-acre lot that's not much more than
> half lawn sometimes brings me close to 50% DoD, occasionally perhaps
> very slightly below. It took a bit of convincing myself to spend $1K
> on batteries—almost twice what I spent on the Motenergy ME1004 motor.
> Part of what got in the way of accepting that reality early on was a
> silly idea that I could fit everything under the existing hood and it
> would look the same, just be quieter. Things got a lot easier when I
> decided to ditch the "hood" and embrace as part of the conversion the
> fact that this was going to look way different when I was done. If I
> were starting over today, I'd seriously consider getting together with
> friends on breaking a scavenged Volt battery and doing a 2p15s or
> 3p15s arrangement (I don't recall the capacity of the volt cells).
> Scavenged Volt batteries seem to be going for around $2K so if enough
> people wanted to get together on it, this would have been an
> opportunity to get more capacity for less money. I hope that by the
> time my current batteries are going downhill, lithium cells are a dime
> a dozen.
>
> Installing muffin fans pulling cooling air through a reticulated foam
> filter (like they use for aquariums) to provide positive pressure
> cleaned air in a plenum around the motor was a good idea. The motor
> stays clean. I don't know if it matters for cooling, since I'm running
> the motor well under rated load. But cleaned air can't hurt brush
> life. I count that as worth the 1.2A continuous draw. Using plexiglass
> to make that plenum was a great idea. Using 1/8" plexiglas for the
> sides and 1/4" only for the top where the muffin fans were mounted was
> a false economy; if I were doing it again I would make the whole
> plenum out of the more expensive, but more robust and easier to work
> 1/4" plexiglass. Given the frame I had to build to support the 1/8"
> plexiglass, I think that it would have taken me less than half the
> time if I'd done it all in 1/4" plexiglass. However, using a sectional
> picture frame (the kind where you purchase two packages to make one
> frame, one package for each dimension) as the holder for the
> reticulated foam worked quite well. I'd do the same thing again even
> if I weren't so incredibly lucky as to find the frame packages on sale
> for 95% off... I used a combination of glue and brass screws to hold
> the plexiglass together; if I were doing it again I'd just use the
> brass screws. They look pretty cool in the plexiglass box if I do say
> so myself.
>
> Talking myself into doubling my 4awg welding cable for the equivalent
> cross sectional area of 1awg was almost certainly overkill. Joe
> Lorenzi has 8awg in his JD with the same motor, and he told me that it
> gets a little warm and thicker than 8awg would be useful, but I really
> don't think I need 1awg equivalent. Even immediately after mowing
> through thick grass with no breaks for nearly half an hour (down to
> 50%DoD) my cables are cold. If I were doing it over, I would just use
> the 4awg cable. Would be easier and use lighter, easier-to-manage
> lugs, and routing would be less of a challenge than it was.
>
> I bought both 400A and 200A fuses, not sure whether it would blow the
> 200A fuse. I needn't have worried. I do see over 100A continuous, but
> the 200A fuse hasn't blown. The batteries just can't push that much
> current through that motor...
>
> Hooking up my power switch so that the charging cable is connected in
> one direction, and the contactor in the other, means that I can't
> accidentally try to charge it and run it at the same time, and makes
> it less likely that I'll drive away and leave the charger connected.
> Buying SB50 anderson connectors for charging at 48V 6A max was silly;
> the charger came with C15 (just like in the back of your computer)
> which works fine. So I have some unused SB50 anderson connectors...
>
> I was originally going to connect both sides of the motor through an
> SB350 anderson connector for a disconnect. Instead, I put a single
> pole PP disconnect (using exactly the same internals as the SB350)
> inline next to the fuse as my emergency disconnect / safety
> maintenance disconnect. Requires only half the effort to pull it open
> in an emergency, and the loop of wire that doubles as the emergency
> disconnect handle is also convenient for my clamp ammeter! So I also
> have some unused SB350 anderson connectors...
>
> I wanted to avoid a 12V house battery and run everything off of 48V
> due to my initial expectation to install one of my batteries under the
> seat, before I settled on the 9A31 batteries that couldn't possibly
> fit. After deciding on batteries, I didn't go back and reconsider my
> design. Because of that, it was hard to source the muffin fans (found
> surplus fan FRU for rack-mounted hardware), and the contactor solenoid
> draws more power than it otherwise would. And now I need 12V house
> power anyway if only because the amphour meter I purchased requires
> isolated 12V power, so I intend to put the original starting battery
> back in the empty hole under the seat and use it for house power, and
> regret that it's not running my fans and contactor since they are 48V
> units. It also got in the way of taking Lee Hart's excellent advice
> for using two contactors to reduce the power draw. And it also kept me
> from hooking up the safety interlocks — which it turns out would be
> more of a pain than I expected for other reasons, so even when I add
> the house battery I'm not sure I'll get the safety interlocks
> connected. I do keep that in mind when using it, though. I did spend
> my early childhood (as soon as I could physically reach the pedals)
> driving around a couple of simplicity tractors with no interlocks...
>
> The MTD transmatic belt-and-pully variable transmission isn't as bad
> as I thought (it's not hydrostatic and by most reports it's more
> efficient than a hydrostatic), but it's really imperative to get the
> MTD belts and not belts advertised as "OEM replacement". The non-MTD
> belts were both unsafe (the tractor wouldn't come to a complete stop)
> and were so sticky that they cost me something like 20A. Also, using
> them damaged the transmission a bit and made it harder to shift,
> though that's gotten better since I replaced them with the MTD belts.
>
> I was surprised to find that the bearings in the mower deck were free
> and turned easily; I had expected to have to refurbish them but did
> not have to do so in the end. I did replace the mower blades.
>
> Having two of the batteries cantilevered over the front tires requires
> excessive tire pressure and makes steering a lot of work. There is way
> more weight forward than in the ICE configuration. I expect to replace
> the steering pinion every few years; the first one lasted about 7
> years but this is much heavier service. Having the other two batteries
> between the console and the seat such that I have to straddle them
> while I drive works, but it doesn't put enough weight at the back, so
> I sometimes have to shift my weight to the back of the tractor to keep
> the rear tires from spinning. The advice to instead mount them
> cantilevered off the back of the tractor was good; I didn't do it
> because it would get in the way of bagging. I normally mulch, but I
> bag when I mow leaves in the fall. So I don't think I personally would
> change that, but for anyone else considering this, if you don't need
> to bag, I'd strongly suggest considering mounting rear batteries
> behind the seat for better traction and balance. Better still would be
> lighter batteries, like the broken Volt battery idea, or other lithium
> ion, that can source the current and won't be hurt by much deeper
> discharge. Would have taken a different charger, of course.
>
> Mounting a wood bumper in front of the front batteries to protect them
> was a good idea. Especially when I had the non-MTD belts installed
> that didn't come to a complete stop. That protected those expensive
> AGM batteries!
>
> I definitely expect to have to sharpen the blades often; they will
> draw more current if they are dull. If I remove the batteries, I can
> easily and safely tip the tractor on its side to sharpen the blades.
> I'd like to be very clear that this isn't advice or a recommendation.
> But in doing that I know for sure that the motor can't start while I'm
> trying to sharpen the blades! ☺
>
> I did use a DPDT on-off-on switch to connect positive pole to either
> the contactor or the charger, and I routed through both poles in
> series so that each half sees 24V for less arcing in the switch for
> longer life. I have not yet built a snubber, though on an oscilloscope
> I measured a 1ms -100V pulse from the contactor solenoid. Basically,
> that means that I got a 1ms -100V pulse with a 10MOhm 15pF RC snubber.
> ☺ I finally got an assortment of rectifier diodes and high voltage
> polypropylene capacitors so I can cook up a RCD snubber to put on the
> contactor solenoid thanks to Lee's excellent page on the
> characteristics of various types of snubbers. No need to snub the
> permanent magnet DC motor; I couldn't measure any back-EMF from it and
> I have a vague sense that's typical due to the permittivity of
> permanent magnets.
>
> I'm considering making a simple PWM motor controller for the fans
> since I think they are probably way overkill and I could reduce the
> 1.2A draw. But first I need the snubber to keep the power cleaner. One
> I have that, I have a HV buck converter to supply the control circuit,
> and it just takes a 555 timer, resistor, potentiometer, a few
> capacitors, a few diodes, and a MOSFET to reduce the power draw from
> the fans. But there's really no need. That would be just for fun.
>
> I have not built the battery balancers. The batteries are all within
> .02V of each other so far. The one balancer I built was a pain to
> build. I can't figure out how Lee manages to solder the diodes to the
> lugs without overheating the diodes. I had already ordered the parts
> from mouser before I saw that Lee was selling them, at which point I
> thought I'd just build them, and then I discovered what a pain that is
> and gave up after building one that I don't really trust because the
> zeners got so hot while I was soldering them into the lugs, despite my
> best efforts. So if my batteries start getting out of balance, I think
> I'll just cut my losses and buy a set from Lee who knows what he's
> doing. I'll just add the zeners etc. to my kit of random electronics
> parts and someday find a use for them.
>
> Oh, and it seems like everyone I talk to about my project exclaims
> about how cool it is that I can mow my lawn silently. Maybe they are
> remembering how a Leaf or Prius or (if they are lucky) a Tesla can
> sneak up on them. My motor running alone on the bench was
> uncomfortably loud and I wore ear plugs for comfort when I was
> breaking in the brushes while it was on the bench in the workshop.
> Before the conversion, the ICE was louder than the mower deck but the
> mower deck made the tractor much louder when it was engaged. Now, the
> mower deck is much louder than the motor. I still wear ear plugs while
> I mow the lawn.
>
> But still, with all the mistakes and downsides and things I'd do
> differently next time, I still get the EV grin while using it, which
> is impressive since I really really hate to mow the lawn. Making me
> happy while I mow the lawn is a definite accomplishment.
> _______________________________________________
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Re: Lawn tractor conversion: lessons learned

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On Tue, Jul 29, 2014 at 1:30 PM, Lee Hart <[hidden email]> wrote:
> Michael K Johnson via EV wrote:
>> I'd seriously consider getting together with friends on a scavenged
>> Volt battery...
>
> That could be fun as an experiment, but could cost more and require more
> finesse to get it all to work. Dumb old lead-acids are easier, and a
> reasonable first-EV solution.

Well, a few months after I bought my batteries, a friend bought a few
scavenged volt batteries, and it literally would have cost me less than
the $1K I paid for the SLAs to have more capacity with greater
available discharge. So I'm not being crazy here.  I would have needed
a different charger for lithium, though. That's where the money would
have gone.

> Putting the motor in a pressurized box is an interesting solution. The foam
> filters apparently have a low enough pressure drop to work with
> propeller-type fans. The more common approach uses a squirrel-cage blower
> with a higher-drop filter element.

The plenum exhaust area is about 2x12" and the frame around it stays
clean; it's clearly moving a lot of air. I do brush off the filter after each
mowing session because it collects detritus around the intakes. I
sized the frame just small enough for a good interference fit.

> Is it "real" plexiglass (brittle acrylic), or the more common polycarbonate
> (slightly flexible, nearly unbreakable)? Polycarbonate is so strong that
> even 1/8" would be indestructible.

Acrylic. Polycarbonate is more expensive and really hard to work,
as your point about the indestructibility of 1/8" stock attests to.  If I
had gone with 1/4" acrylic for the whole box, I could have used
simple butt joints and screwed the pieces together and it would
have been far less work.

I did find out a couple weeks too late that I could have brought the
acrylic to a friend and co-worker who would have cut it for me with
his laser cutter. Maybe next winter... ☺

> Well, it's a small matter. Your wire lengths are short, so not a lot of loss
> no matter how you do it. What ulitmately matters is that the wire doesn't
> get hot, and you've certainly achieved that.

It's a small amount of extra money in the grand scheme of the
conversion, and I don't really regret it. I'm merely recording for
the next person that my impression was that it was overkill for
the tractor.  I don't think these batteries can source enough current
to overheat 4awg; they start noticeably sagging around 140A-150A.
Might be different with lithium.

>> Buying SB50 anderson connectors for charging at 48V 6A max was silly;
>
> But, they are very robust and will last. They can carry 6a even when dirty,
> worn, and corroded. Maybe you'll get a higher current charger someday. (Your
> AGMs might like higher-current charging anyway).

I cut the female end off a C15-C15 extension, and used the male C15 end of
the cord for my charging circuit. I used liquid electrical tape (many layers)
to cover the conductors coming out of the cut-off end of the cord, and keep
the male end plugged into that cut-off plug to keep the male connector
clean when I am not charging the traction batteries.

But if I ever make one of the open source chargers that can dump more than
6A into the batteries, I'll keep the SB50s in mind, of course.

$1200-1400 for the EMW kit is more than I want to spend on that right now.
I'm still recovering from blowing the budget in the first place.

> 48v input to 12v output DC/DC converters are pretty common; the Telco
> industry used them in quantity. You can probably find one surplus for
> $10-$20 that can run fans, contactor coils, and your amphour meter.

As it turns out, the old 12V battery is toast. But I have some SLA batteries
that UPS units were complaining about but which have lots of life left in
them and I'll use them for house. Even cheaper than buying an isolated
converter. Of course I don't have a 12V charger handy, so I cobbled together
the power supply from a dead laptop, a buck converter with a CV regulator,
some wires scavenged from a dying coffee mater, and my meter to make
sure I'm within spec, and voila, a charger!

Someone else could use a converter to run fans and contactor coils,
but since I have 48V fans and contactor coils, I'd have to replace them
to switch, and that doesn't seem worthwhile.

The 48V fans came out of telco gear where 48V is, as you point out, common.

> If that's a worry, 48v contactor coils are very common.

That's what I have. I just seem to recall that the 48V contactor coils
drew more current than the 12V in the same series (Alltrax).

> On snowmobiles and other users of this variable-pulley-size method, they
> sometimes use metal belts (chains) with little friction pads on the sides.
> They are more efficient than the typical rubber v-belts. Maybe one is
> available for the size needed here?

I doubt it. This is a long belt and needs to flex and runs through
frankly poorly-guided space. I'll stick with OEM and would suggest
the same for anyone trying to convert similar tractors.

> With EVs, an ammeter makes it easy to *tell* when it's using more power.
> With an ICE, there's no way to tell it's burning more gas.

Well, I could certainly hear the difference in sound from the ICE when
it was loaded. I could definitely tell. It's just easier to ignore the problem
when you can just pour more fuel in the tank than having to stop and
recharge overnight when you are "out of juice".

> Glad it helped! An oscilloscope is the perfect way to pick the snubber
> parts. You can easily see when you have good values. Add capacitance until
> the peak voltage is reasonable, then add resistance until the ringing is
> just about gone.

That's the clearest description I've seen yet of the experimental process
for building an RC snubber!

>> I'm considering making a simple PWM motor controller for the fans
>
> For this to work, they have to be simple motors -- not brushless DC motors
> with electronics. Almost all small fan motors are now brushless DC.
>
> To use a PWM controller with a brushless DC fan, you'll have to add your own
> series inductor and filter capacitor on the PWM output (a proper buck
> converter) so you get smooth filtered DC out.

Indeed, they are brushless. Not much point. Thanks!

> I fold the diode lead back along the body. Insert the diode into the lug
> (the folded lead holds it in place). I solder the end of the lead wire to
> the inside of the lug with a BIG soldering iron, which can heat the lug up
> quickly. Add solder to solder the wire to the inside of the lug. It then
> cools quickly, because only that one small area of the lug was heated to
> soldering temperature.

Ah, and with curved hemostats I can then heat-sink the diodes while
soldering. I feel better with that design.

But I might still buy them from you anyway. ☺

> That's surprising. It should have sounded like a vacuum cleaner motor; not
> particularly loud, but perhaps annoying because there's a whistle-like pitch
> to it.

I think I'm more sensitive to noise than most; I find vacuum cleaners
annoying too. It sounds similar to the videos that Joe posted of his
conversion. I don't think it's a faulty motor sample.
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Re: Lawn tractor conversion: lessons learned

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Thanks Michael for the very useful and thorough discussion. I hope to do an
EV mower soon.

Al

----- Original Message -----
From: "Michael K Johnson via EV" <[hidden email]>
To: "Electric Vehicle Discussion List" <[hidden email]>
Sent: Monday, July 28, 2014 10:59 PM
Subject: [EVDL] Lawn tractor conversion: lessons learned


>I got lots of useful help here on my lawn tractor conversion project —
> http://www.evalbum.com/4841 — so I thought I'd post some lessons
> learned, both positive and negative. None of this is intended as
> advice for anyone else, for obvious reasons. I'm not doing everything
> as safely as I might! This is just the "brain dump" I wish someone
> else had written for me to read when I was getting started.
>
> Biting the bullet and buying real batteries (Deka Intimidator 9A31)
> was a good idea. Mowing my half-acre lot that's not much more than
> half lawn sometimes brings me close to 50% DoD, occasionally perhaps
> very slightly below. It took a bit of convincing myself to spend $1K
> on batteries—almost twice what I spent on the Motenergy ME1004 motor.
> Part of what got in the way of accepting that reality early on was a
> silly idea that I could fit everything under the existing hood and it
> would look the same, just be quieter. Things got a lot easier when I
> decided to ditch the "hood" and embrace as part of the conversion the
> fact that this was going to look way different when I was done. If I
> were starting over today, I'd seriously consider getting together with
> friends on breaking a scavenged Volt battery and doing a 2p15s or
> 3p15s arrangement (I don't recall the capacity of the volt cells).
> Scavenged Volt batteries seem to be going for around $2K so if enough
> people wanted to get together on it, this would have been an
> opportunity to get more capacity for less money. I hope that by the
> time my current batteries are going downhill, lithium cells are a dime
> a dozen.
>
> Installing muffin fans pulling cooling air through a reticulated foam
> filter (like they use for aquariums) to provide positive pressure
> cleaned air in a plenum around the motor was a good idea. The motor
> stays clean. I don't know if it matters for cooling, since I'm running
> the motor well under rated load. But cleaned air can't hurt brush
> life. I count that as worth the 1.2A continuous draw. Using plexiglass
> to make that plenum was a great idea. Using 1/8" plexiglas for the
> sides and 1/4" only for the top where the muffin fans were mounted was
> a false economy; if I were doing it again I would make the whole
> plenum out of the more expensive, but more robust and easier to work
> 1/4" plexiglass. Given the frame I had to build to support the 1/8"
> plexiglass, I think that it would have taken me less than half the
> time if I'd done it all in 1/4" plexiglass. However, using a sectional
> picture frame (the kind where you purchase two packages to make one
> frame, one package for each dimension) as the holder for the
> reticulated foam worked quite well. I'd do the same thing again even
> if I weren't so incredibly lucky as to find the frame packages on sale
> for 95% off... I used a combination of glue and brass screws to hold
> the plexiglass together; if I were doing it again I'd just use the
> brass screws. They look pretty cool in the plexiglass box if I do say
> so myself.
>
> Talking myself into doubling my 4awg welding cable for the equivalent
> cross sectional area of 1awg was almost certainly overkill. Joe
> Lorenzi has 8awg in his JD with the same motor, and he told me that it
> gets a little warm and thicker than 8awg would be useful, but I really
> don't think I need 1awg equivalent. Even immediately after mowing
> through thick grass with no breaks for nearly half an hour (down to
> 50%DoD) my cables are cold. If I were doing it over, I would just use
> the 4awg cable. Would be easier and use lighter, easier-to-manage
> lugs, and routing would be less of a challenge than it was.
>
> I bought both 400A and 200A fuses, not sure whether it would blow the
> 200A fuse. I needn't have worried. I do see over 100A continuous, but
> the 200A fuse hasn't blown. The batteries just can't push that much
> current through that motor...
>
> Hooking up my power switch so that the charging cable is connected in
> one direction, and the contactor in the other, means that I can't
> accidentally try to charge it and run it at the same time, and makes
> it less likely that I'll drive away and leave the charger connected.
> Buying SB50 anderson connectors for charging at 48V 6A max was silly;
> the charger came with C15 (just like in the back of your computer)
> which works fine. So I have some unused SB50 anderson connectors...
>
> I was originally going to connect both sides of the motor through an
> SB350 anderson connector for a disconnect. Instead, I put a single
> pole PP disconnect (using exactly the same internals as the SB350)
> inline next to the fuse as my emergency disconnect / safety
> maintenance disconnect. Requires only half the effort to pull it open
> in an emergency, and the loop of wire that doubles as the emergency
> disconnect handle is also convenient for my clamp ammeter! So I also
> have some unused SB350 anderson connectors...
>
> I wanted to avoid a 12V house battery and run everything off of 48V
> due to my initial expectation to install one of my batteries under the
> seat, before I settled on the 9A31 batteries that couldn't possibly
> fit. After deciding on batteries, I didn't go back and reconsider my
> design. Because of that, it was hard to source the muffin fans (found
> surplus fan FRU for rack-mounted hardware), and the contactor solenoid
> draws more power than it otherwise would. And now I need 12V house
> power anyway if only because the amphour meter I purchased requires
> isolated 12V power, so I intend to put the original starting battery
> back in the empty hole under the seat and use it for house power, and
> regret that it's not running my fans and contactor since they are 48V
> units. It also got in the way of taking Lee Hart's excellent advice
> for using two contactors to reduce the power draw. And it also kept me
> from hooking up the safety interlocks — which it turns out would be
> more of a pain than I expected for other reasons, so even when I add
> the house battery I'm not sure I'll get the safety interlocks
> connected. I do keep that in mind when using it, though. I did spend
> my early childhood (as soon as I could physically reach the pedals)
> driving around a couple of simplicity tractors with no interlocks...
>
> The MTD transmatic belt-and-pully variable transmission isn't as bad
> as I thought (it's not hydrostatic and by most reports it's more
> efficient than a hydrostatic), but it's really imperative to get the
> MTD belts and not belts advertised as "OEM replacement". The non-MTD
> belts were both unsafe (the tractor wouldn't come to a complete stop)
> and were so sticky that they cost me something like 20A. Also, using
> them damaged the transmission a bit and made it harder to shift,
> though that's gotten better since I replaced them with the MTD belts.
>
> I was surprised to find that the bearings in the mower deck were free
> and turned easily; I had expected to have to refurbish them but did
> not have to do so in the end. I did replace the mower blades.
>
> Having two of the batteries cantilevered over the front tires requires
> excessive tire pressure and makes steering a lot of work. There is way
> more weight forward than in the ICE configuration. I expect to replace
> the steering pinion every few years; the first one lasted about 7
> years but this is much heavier service. Having the other two batteries
> between the console and the seat such that I have to straddle them
> while I drive works, but it doesn't put enough weight at the back, so
> I sometimes have to shift my weight to the back of the tractor to keep
> the rear tires from spinning. The advice to instead mount them
> cantilevered off the back of the tractor was good; I didn't do it
> because it would get in the way of bagging. I normally mulch, but I
> bag when I mow leaves in the fall. So I don't think I personally would
> change that, but for anyone else considering this, if you don't need
> to bag, I'd strongly suggest considering mounting rear batteries
> behind the seat for better traction and balance. Better still would be
> lighter batteries, like the broken Volt battery idea, or other lithium
> ion, that can source the current and won't be hurt by much deeper
> discharge. Would have taken a different charger, of course.
>
> Mounting a wood bumper in front of the front batteries to protect them
> was a good idea. Especially when I had the non-MTD belts installed
> that didn't come to a complete stop. That protected those expensive
> AGM batteries!
>
> I definitely expect to have to sharpen the blades often; they will
> draw more current if they are dull. If I remove the batteries, I can
> easily and safely tip the tractor on its side to sharpen the blades.
> I'd like to be very clear that this isn't advice or a recommendation.
> But in doing that I know for sure that the motor can't start while I'm
> trying to sharpen the blades! ☺
>
> I did use a DPDT on-off-on switch to connect positive pole to either
> the contactor or the charger, and I routed through both poles in
> series so that each half sees 24V for less arcing in the switch for
> longer life. I have not yet built a snubber, though on an oscilloscope
> I measured a 1ms -100V pulse from the contactor solenoid. Basically,
> that means that I got a 1ms -100V pulse with a 10MOhm 15pF RC snubber.
> ☺ I finally got an assortment of rectifier diodes and high voltage
> polypropylene capacitors so I can cook up a RCD snubber to put on the
> contactor solenoid thanks to Lee's excellent page on the
> characteristics of various types of snubbers. No need to snub the
> permanent magnet DC motor; I couldn't measure any back-EMF from it and
> I have a vague sense that's typical due to the permittivity of
> permanent magnets.
>
> I'm considering making a simple PWM motor controller for the fans
> since I think they are probably way overkill and I could reduce the
> 1.2A draw. But first I need the snubber to keep the power cleaner. One
> I have that, I have a HV buck converter to supply the control circuit,
> and it just takes a 555 timer, resistor, potentiometer, a few
> capacitors, a few diodes, and a MOSFET to reduce the power draw from
> the fans. But there's really no need. That would be just for fun.
>
> I have not built the battery balancers. The batteries are all within
> .02V of each other so far. The one balancer I built was a pain to
> build. I can't figure out how Lee manages to solder the diodes to the
> lugs without overheating the diodes. I had already ordered the parts
> from mouser before I saw that Lee was selling them, at which point I
> thought I'd just build them, and then I discovered what a pain that is
> and gave up after building one that I don't really trust because the
> zeners got so hot while I was soldering them into the lugs, despite my
> best efforts. So if my batteries start getting out of balance, I think
> I'll just cut my losses and buy a set from Lee who knows what he's
> doing. I'll just add the zeners etc. to my kit of random electronics
> parts and someday find a use for them.
>
> Oh, and it seems like everyone I talk to about my project exclaims
> about how cool it is that I can mow my lawn silently. Maybe they are
> remembering how a Leaf or Prius or (if they are lucky) a Tesla can
> sneak up on them. My motor running alone on the bench was
> uncomfortably loud and I wore ear plugs for comfort when I was
> breaking in the brushes while it was on the bench in the workshop.
> Before the conversion, the ICE was louder than the mower deck but the
> mower deck made the tractor much louder when it was engaged. Now, the
> mower deck is much louder than the motor. I still wear ear plugs while
> I mow the lawn.
>
> But still, with all the mistakes and downsides and things I'd do
> differently next time, I still get the EV grin while using it, which
> is impressive since I really really hate to mow the lawn. Making me
> happy while I mow the lawn is a definite accomplishment.
> _______________________________________________
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> (http://groups.yahoo.com/group/NEDRA)
>
>

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Re: Lawn tractor conversion: lessons learned

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New lesson learned this weekend.

On Mon, Jul 28, 2014 at 10:59 PM, Michael K Johnson <[hidden email]> wrote:
> Talking myself into doubling my 4awg welding cable for the equivalent
> cross sectional area of 1awg was almost certainly overkill. Joe
> Lorenzi has 8awg in his JD with the same motor, and he told me that it
> gets a little warm and thicker than 8awg would be useful, but I really
> don't think I need 1awg equivalent. Even immediately after mowing
> through thick grass with no breaks for nearly half an hour (down to
> 50%DoD) my cables are cold. If I were doing it over, I would just use
> the 4awg cable. Would be easier and use lighter, easier-to-manage
> lugs, and routing would be less of a challenge than it was.

I changed my mind this weekend.

To prepare for aeration and overseeding, I mowed my lawn short. I
normally mow with the deck raised to maximum height (good for
fescue lawns), but to prepare to aerate and overseed, I nearly
scalped the lawn. I still mulched while doing this to create cover
for the seeds when overseeding. Cutting the grass low takes far
more power; so much so that a few times the cutting blades
nearly stalled. Normally I can mow front and back without exceeding
50% DoD while mowing up to 26 minutes. Cutting just the front,
taking well under 20 minutes (going slowly), I significantly exceeded
50% DoD. Don't know exactly how much because I couldn't let
the battery rest to get a precise measurement; I had to charge right
away to keep going in order to finish the project this weekend.

What clued me in to bring the mower back in to charge very early
was that the 2 4awg cables (1awg cross sectional equivalent)
were quite warm to the touch. Not too hot to touch, but perhaps
50⁰C.

I don't know how much current I was drawing, but in any case I
now feel that 1awg equivalent was a good choice, and if I ever
get stiffer batteries, I'll want to consider even larger wires.

Roland, thanks for recommending that I double the wires!

> I bought both 400A and 200A fuses, not sure whether it would blow the
> 200A fuse. I needn't have worried. I do see over 100A continuous, but
> the 200A fuse hasn't blown. The batteries just can't push that much
> current through that motor...

Even while bogged down, with the blades occasionally almost stallling
when the deck started getting clogged, and the wires getting warm, the
200A fuse did not blow.
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Re: Lawn tractor conversion: lessons learned

Adam45
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Hello dear, if you are really looking to buy Lawn Mower, you should try buying it from Lawn Mower Sales Roswell as they are providing heavy discounts and trust me the product will be genuine for sure.
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Re: Lawn tractor conversion

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Michael,

Hard to believe you made this post 2 years ago - I've been holding on to
a few of these for a plan of my own.

I've now cut the grass half a dozen times with my electric tractor
conversion.  I've wanted to convert something bigger for ages, but I've
had to settle for starting small first.

I have had some fun just driving around in a nearly silent go-kart, that
just happens to also serve a useful purpose when I turn on the mower
deck. :)

Pictures -
http://www.tmcom.com/~tsm1/gallery2/main.php?g2_itemId=2060050

Action video - I should get some audio to overlay on it, but haven't.
https://youtu.be/wUHULS-56vo

Brief synopsis:

Used Craftsman 42" / 15.5hp tractor, with a hole in the block.

It sat for a few years before I finally pulled the trigger on the
conversion.

EVDrives supplied an ME1004 and 48V contactor.

I pulled the gas engine/fuel tank/muffler and then fabricated an
aluminum engine adapter plate, along with a spacer for the pulleys -
while the pulley fit the shaft just fine, I had some height to adjust.

I wound up using some reduced head "header" bolts in a few spots on the
motor mount - mostly to avoid cutting the tractor frame to make it all
fit (this way I kept the rolled lip around the old engine opening).

At one point, I had a line on some used 80AH 12V UPS batteries, but I
didn't grab them at the time.. and after much contemplation, I bought a
Chevy Volt pack from Hybrid Auto Center.  12S1P, "48V" pack, charge &
balance BMS, and a 9amp charger.

The motor was ~$600, the battery and accessories another ~$800 IIRC.  
Yes, I could've just bought a new gas tractor (or just kept using the
gas tractor I already/still have) for less.

(4 12V lead batteries at ~$150 each came in closer to the Lithium cost,
at greater weight and packaging problems, and likely reduced life)

This is a 47ah battery, or 2kwh.  Charges to 50V, and I stop what I'm
doing when I discharge to 42V.

The Volt battery sits where the muffler used to be.  I have room to put
a second battery between the electric motor and the dash if I had to,
and maybe a third under the seat / above the transaxle.

This mower uses a 6spd transaxle.

So, 48V relay, 400amp fuse.

My wires are a hodgepodge - the negative cable is a short run of 2/0
cable I had lying around.  The positive has a 2g battery lead to the
fuse, because I had a used automotive battery cable that was 2g.  Then
the fuse to relay, and relay to motor is doubled-up 4g cables in both
cases - because I had other used automotive battery cables.  (Bad ends
removed, new ends crimped in the right spots, etc - just used wire saved
for this purpose).

None of the wires seem to get hot - the motor is more hot than the wires.

The short story is it works great.  The 2kwh Lithium pack between 50V
and 42V yields around 20 minutes of mowing time with the deck going.  It
is enough to mow either my front or my back yard.  So I can mow one,
charge over night, and mow the other.  OTOH, if I stay on top of it and
focus on the task at hand, I can do either side in a little over 10
minutes - so maybe with a little more practice, I could get to do the
entire yard in one charge.

A second battery would solve that, of course - but the current situation
is very workable.

I had hoped for 15 minutes to an hour of mowing, depending on actual amp
draw.  I seem to be closer to the 125amp side of things (125amps @ 45v
for 1/3 of an hour is 1.873kwh).  I have not tried just "driving" around
to see if I can make it to the corner store and back on one charge.  6th
gear isn't as fast as I'd like for that.

I haven't noticed the electric motor "bog" down like my ICE mower does
from time to time - it just pours on the torque.

You get a little bit of a whir and whine driving it around - but
compared to the ICE, it is silent.  It does still make a racket when you
start spinning the blades.

On the over-doing-it side, I also bought a ~$6 48V to 12V water-proof
down-converter to run the headlights, rather than a "house" battery.  I
also added some power-poles, so I could conceivably use the 2kwh pack to
run the radios during Field Day just because.

So far so good - mowing the lawn hasn't been this fun since I was a kid
and didn't know that mowing the lawn was a chore. :D


So - thank you, Michael, for posting your plan and your follow up.

I hope mine helps the next one..

-Tom

On 7/28/2014 8:59 PM, Michael K Johnson via EV wrote:

> I got lots of useful help here on my lawn tractor conversion project —
> http://www.evalbum.com/4841 — so I thought I'd post some lessons
> learned, both positive and negative. None of this is intended as
> advice for anyone else, for obvious reasons. I'm not doing everything
> as safely as I might! This is just the "brain dump" I wish someone
> else had written for me to read when I was getting started.
>
> Biting the bullet and buying real batteries (Deka Intimidator 9A31)
> was a good idea. Mowing my half-acre lot that's not much more than
> half lawn sometimes brings me close to 50% DoD, occasionally perhaps
> very slightly below. It took a bit of convincing myself to spend $1K
> on batteries—almost twice what I spent on the Motenergy ME1004 motor.
> Part of what got in the way of accepting that reality early on was a
> silly idea that I could fit everything under the existing hood and it
> would look the same, just be quieter. Things got a lot easier when I
> decided to ditch the "hood" and embrace as part of the conversion the
> fact that this was going to look way different when I was done. If I
> were starting over today, I'd seriously consider getting together with
> friends on breaking a scavenged Volt battery and doing a 2p15s or
> 3p15s arrangement (I don't recall the capacity of the volt cells).
> Scavenged Volt batteries seem to be going for around $2K so if enough
> people wanted to get together on it, this would have been an
> opportunity to get more capacity for less money. I hope that by the
> time my current batteries are going downhill, lithium cells are a dime
> a dozen.
>
> Installing muffin fans pulling cooling air through a reticulated foam
> filter (like they use for aquariums) to provide positive pressure
> cleaned air in a plenum around the motor was a good idea. The motor
> stays clean. I don't know if it matters for cooling, since I'm running
> the motor well under rated load. But cleaned air can't hurt brush
> life. I count that as worth the 1.2A continuous draw. Using plexiglass
> to make that plenum was a great idea. Using 1/8" plexiglas for the
> sides and 1/4" only for the top where the muffin fans were mounted was
> a false economy; if I were doing it again I would make the whole
> plenum out of the more expensive, but more robust and easier to work
> 1/4" plexiglass. Given the frame I had to build to support the 1/8"
> plexiglass, I think that it would have taken me less than half the
> time if I'd done it all in 1/4" plexiglass. However, using a sectional
> picture frame (the kind where you purchase two packages to make one
> frame, one package for each dimension) as the holder for the
> reticulated foam worked quite well. I'd do the same thing again even
> if I weren't so incredibly lucky as to find the frame packages on sale
> for 95% off... I used a combination of glue and brass screws to hold
> the plexiglass together; if I were doing it again I'd just use the
> brass screws. They look pretty cool in the plexiglass box if I do say
> so myself.
>
> Talking myself into doubling my 4awg welding cable for the equivalent
> cross sectional area of 1awg was almost certainly overkill. Joe
> Lorenzi has 8awg in his JD with the same motor, and he told me that it
> gets a little warm and thicker than 8awg would be useful, but I really
> don't think I need 1awg equivalent. Even immediately after mowing
> through thick grass with no breaks for nearly half an hour (down to
> 50%DoD) my cables are cold. If I were doing it over, I would just use
> the 4awg cable. Would be easier and use lighter, easier-to-manage
> lugs, and routing would be less of a challenge than it was.
>
> I bought both 400A and 200A fuses, not sure whether it would blow the
> 200A fuse. I needn't have worried. I do see over 100A continuous, but
> the 200A fuse hasn't blown. The batteries just can't push that much
> current through that motor...
>
> Hooking up my power switch so that the charging cable is connected in
> one direction, and the contactor in the other, means that I can't
> accidentally try to charge it and run it at the same time, and makes
> it less likely that I'll drive away and leave the charger connected.
> Buying SB50 anderson connectors for charging at 48V 6A max was silly;
> the charger came with C15 (just like in the back of your computer)
> which works fine. So I have some unused SB50 anderson connectors...
>
> I was originally going to connect both sides of the motor through an
> SB350 anderson connector for a disconnect. Instead, I put a single
> pole PP disconnect (using exactly the same internals as the SB350)
> inline next to the fuse as my emergency disconnect / safety
> maintenance disconnect. Requires only half the effort to pull it open
> in an emergency, and the loop of wire that doubles as the emergency
> disconnect handle is also convenient for my clamp ammeter! So I also
> have some unused SB350 anderson connectors...
>
> I wanted to avoid a 12V house battery and run everything off of 48V
> due to my initial expectation to install one of my batteries under the
> seat, before I settled on the 9A31 batteries that couldn't possibly
> fit. After deciding on batteries, I didn't go back and reconsider my
> design. Because of that, it was hard to source the muffin fans (found
> surplus fan FRU for rack-mounted hardware), and the contactor solenoid
> draws more power than it otherwise would. And now I need 12V house
> power anyway if only because the amphour meter I purchased requires
> isolated 12V power, so I intend to put the original starting battery
> back in the empty hole under the seat and use it for house power, and
> regret that it's not running my fans and contactor since they are 48V
> units. It also got in the way of taking Lee Hart's excellent advice
> for using two contactors to reduce the power draw. And it also kept me
> from hooking up the safety interlocks — which it turns out would be
> more of a pain than I expected for other reasons, so even when I add
> the house battery I'm not sure I'll get the safety interlocks
> connected. I do keep that in mind when using it, though. I did spend
> my early childhood (as soon as I could physically reach the pedals)
> driving around a couple of simplicity tractors with no interlocks...
>
> The MTD transmatic belt-and-pully variable transmission isn't as bad
> as I thought (it's not hydrostatic and by most reports it's more
> efficient than a hydrostatic), but it's really imperative to get the
> MTD belts and not belts advertised as "OEM replacement". The non-MTD
> belts were both unsafe (the tractor wouldn't come to a complete stop)
> and were so sticky that they cost me something like 20A. Also, using
> them damaged the transmission a bit and made it harder to shift,
> though that's gotten better since I replaced them with the MTD belts.
>
> I was surprised to find that the bearings in the mower deck were free
> and turned easily; I had expected to have to refurbish them but did
> not have to do so in the end. I did replace the mower blades.
>
> Having two of the batteries cantilevered over the front tires requires
> excessive tire pressure and makes steering a lot of work. There is way
> more weight forward than in the ICE configuration. I expect to replace
> the steering pinion every few years; the first one lasted about 7
> years but this is much heavier service. Having the other two batteries
> between the console and the seat such that I have to straddle them
> while I drive works, but it doesn't put enough weight at the back, so
> I sometimes have to shift my weight to the back of the tractor to keep
> the rear tires from spinning. The advice to instead mount them
> cantilevered off the back of the tractor was good; I didn't do it
> because it would get in the way of bagging. I normally mulch, but I
> bag when I mow leaves in the fall. So I don't think I personally would
> change that, but for anyone else considering this, if you don't need
> to bag, I'd strongly suggest considering mounting rear batteries
> behind the seat for better traction and balance. Better still would be
> lighter batteries, like the broken Volt battery idea, or other lithium
> ion, that can source the current and won't be hurt by much deeper
> discharge. Would have taken a different charger, of course.
>
> Mounting a wood bumper in front of the front batteries to protect them
> was a good idea. Especially when I had the non-MTD belts installed
> that didn't come to a complete stop. That protected those expensive
> AGM batteries!
>
> I definitely expect to have to sharpen the blades often; they will
> draw more current if they are dull. If I remove the batteries, I can
> easily and safely tip the tractor on its side to sharpen the blades.
> I'd like to be very clear that this isn't advice or a recommendation.
> But in doing that I know for sure that the motor can't start while I'm
> trying to sharpen the blades! ☺
>
> I did use a DPDT on-off-on switch to connect positive pole to either
> the contactor or the charger, and I routed through both poles in
> series so that each half sees 24V for less arcing in the switch for
> longer life. I have not yet built a snubber, though on an oscilloscope
> I measured a 1ms -100V pulse from the contactor solenoid. Basically,
> that means that I got a 1ms -100V pulse with a 10MOhm 15pF RC snubber.
> ☺ I finally got an assortment of rectifier diodes and high voltage
> polypropylene capacitors so I can cook up a RCD snubber to put on the
> contactor solenoid thanks to Lee's excellent page on the
> characteristics of various types of snubbers. No need to snub the
> permanent magnet DC motor; I couldn't measure any back-EMF from it and
> I have a vague sense that's typical due to the permittivity of
> permanent magnets.
>
> I'm considering making a simple PWM motor controller for the fans
> since I think they are probably way overkill and I could reduce the
> 1.2A draw. But first I need the snubber to keep the power cleaner. One
> I have that, I have a HV buck converter to supply the control circuit,
> and it just takes a 555 timer, resistor, potentiometer, a few
> capacitors, a few diodes, and a MOSFET to reduce the power draw from
> the fans. But there's really no need. That would be just for fun.
>
> I have not built the battery balancers. The batteries are all within
> .02V of each other so far. The one balancer I built was a pain to
> build. I can't figure out how Lee manages to solder the diodes to the
> lugs without overheating the diodes. I had already ordered the parts
> from mouser before I saw that Lee was selling them, at which point I
> thought I'd just build them, and then I discovered what a pain that is
> and gave up after building one that I don't really trust because the
> zeners got so hot while I was soldering them into the lugs, despite my
> best efforts. So if my batteries start getting out of balance, I think
> I'll just cut my losses and buy a set from Lee who knows what he's
> doing. I'll just add the zeners etc. to my kit of random electronics
> parts and someday find a use for them.
>
> Oh, and it seems like everyone I talk to about my project exclaims
> about how cool it is that I can mow my lawn silently. Maybe they are
> remembering how a Leaf or Prius or (if they are lucky) a Tesla can
> sneak up on them. My motor running alone on the bench was
> uncomfortably loud and I wore ear plugs for comfort when I was
> breaking in the brushes while it was on the bench in the workshop.
> Before the conversion, the ICE was louder than the mower deck but the
> mower deck made the tractor much louder when it was engaged. Now, the
> mower deck is much louder than the motor. I still wear ear plugs while
> I mow the lawn.
>
> But still, with all the mistakes and downsides and things I'd do
> differently next time, I still get the EV grin while using it, which
> is impressive since I really really hate to mow the lawn. Making me
> happy while I mow the lawn is a definite accomplishment.
> _______________________________________________
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>

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Re: Lawn tractor conversion

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On 5 Jun 2016 at 0:45, Tom Mandera via EV wrote:

> The motor was ~$600, the battery and accessories another ~$800 IIRC.  
> Yes, I could've just bought a new gas tractor (or just kept using the
> gas tractor I already/still have) for less.
>

Or a purpose-built electric tractor!  I'm sure you wouldn't get the same
satisfaction or the learning experience you got from conversion, but with
some patience, in that price range you could get a nice used GE Elec-Trac.  

For even less scratch, you could get a fixer-upper ET that you could
probably get up and running with a lot less work than conversion.

There were variations in model numbers later in production and with some of
the later manufacturers who licensed the design from GE, but basically there
were 7 models.  The ER8-36 riding mower was just that and nothing else.  The
E8M light duty tractor with three 12v batteries could also push a dozer
blade for moving snow.  The E10M was an E8M with 6v golf car batteries and
could also handle a snow thrower (though the snow throwers that fit are
scarce).  The E12 / E12M, E15, and E20 all were larger, had heavier
construction, ran on six golf car batteries, and used golf-car type
resistance speed controllers.  These bigger guys accepted a wide range of
attachments including a dozer blade, snow thrower, rear-mounted rototiller,
sickle bar mower, even a hydraulic bucket.  As you'd expect, some of these
goodies are hard to find now and can get a bit pricey.

These tractors all had separate motors for drive and for each mower blade.

In the last few months I've seen offers to sell ETs that vary from a pair of
 large-frame models (E12 and E15) "in need of work" with a bunch of extras
for $300, to a spiffed-up ("refurbished") E10M for $675.  

The most common model is probably the E15.  Going price for one with mower
deck in working condition seems to be around $350-500, with nicer examples
in the $600 and up range.


The smaller machines with three 12v marine batteries (ER8-36 and E8M) will
mow around 1 to 1-1/2 acres, depending on terrain and battery condition.  
The ones with 6 golf car batteries are good for 2-4 acres.  GE claimed up to
5 acres, but I question that.

M-suffix machines and the little ER8-36 rider use belly-mounted mowers.  The
others take front-mounted mowers.  

If anyone's interested in learning more about ETs, contact me off list, and
I'll hook you up with some resources.

David Roden - Akron, Ohio, USA
EVDL Administrator

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