Alternators, DCDC, and air conditioning

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Alternators, DCDC, and air conditioning

Steve Kobb
Help me out here: I'm torn between two competing perspectives on a technical issue.

First, the background: I'm converting a 2002 S-10. Thirteen Trojan 12v batts in the bed; 2 Optima Blue Top D31Ms under the hood. Will probably also get an Iota 55 Amp DCDC to keep the Blue Tops juiced.

I'm in Houston - and that starts with H - and that stands for HEAT. By August, I can barely put my hands on the steering wheel, so a good A/C system is much appreciated.

The guy who's setting up my A/C has been doing auto A/C for many years. He wants to power the compressor with a small motor, which would be run off of the Blue Tops.

And now we get to the controversy: He also wants to add an alternator to pump energy back into the Blue Tops. He's convinced that some of the kinetic energy supplied to the small motor can be recovered by an alternator, which would thus reduce the total amount of energy required by the air conditioning system. Not that he thinks he can CREATE new energy; he just wants to get some of it back.

My mechanical engineering friend says this is an absurd idea because it violates a law of thermodynamics -- I think The Second. The engineer also says that no matter how much energy the alternator might recover, the device won't make up for its own inefficiencies, and therefore is a losing proposition. Net net: I'll wind up with worse performance and worse range than if I had just run the A/C right off the Optimas with no attempt at re-gen.

At this point, I don't know who is more persuasive. My initial attraction to the alternator idea was simply this: If I have to turn a belt that runs the small A/C motor, I might as well ask that belt to turn the alternator, as well.

But that's not how my M.E. buddy sees it... and he can't believe that I'm even giving this alternator idea any serious consideration.

BTW, I've gone through a great many archived EVDL threads on alternators and DCDC. They're all fascinating... and I STILL don't know which perspective to believe.

If you've got any helpful comments on this one, fire away.

Thanks.

Steve

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Re: Alternators, DCDC, and air conditioning

Morgan LaMoore
On Dec 28, 2007 11:55 PM, Steve Kobb <[hidden email]> wrote:
> ...
> But that's not how my M.E. buddy sees it... and he can't believe that I'm
> even giving this alternator idea any serious consideration.

Seriously, trust your Mech E. friend. He's probably spent multiple
semesters studying thermodynamics and systems like this, if his school
is anything like my school. I've seen my roommate who's a Mech E. work
on homework problems that analyze systems like this and calculate
their efficiencies.

The alternator will require more torque and power from your motor,
making it draw more current. You can't come out ahead; the alternator
will only add inefficiency.

-Morgan LaMoore

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Re: Alternators, DCDC, and air conditioning

carrott
In reply to this post by Steve Kobb
On Fri, 2007-12-28 at 21:55 -0800, Steve Kobb wrote:
> At this point, I don't know who is more persuasive. My initial attraction to
> the alternator idea was simply this: If I have to turn a belt that runs the
> small A/C motor, I might as well ask that belt to turn the alternator, as
> well.

This is fairly straightforward to settle. First ignore the air
conditioning compressor and consider your motor and alternator connected
by a belt. It's easy to see that the power produced by the alternator
will always be less than the power consumed by the motor. So doing this
isn't a good idea.

Now consider the air conditioning compressor as well. If you compress
the fluid in the system and then switch off the motor, does the
compressor run backwards? I've never seen this happen but if it did,
then you could capture the energy as the fluid expands using an
alternator. Would it be worth doing? Probably not, especially if you
never turn off the air conditioning (either because the system is too
small for your vehicle or because you use a variable speed system rather
than an on-off to control temperature).

Also, you should consider running your air conditioning motor from the
main traction pack instead of a 12v or 24v accessory battery. You need
on the order of 1kW to drive the air conditioning, this is 83amps at 12v
which is a lot for a small motor.  Your batteries won't like it very
much either. You will also loose some energy converting from your
traction voltage to the accessory voltage. In addition, you could
replace your 2 large accessory batteries with 1 small accessory battery
and a traction battery giving you increased range when not using the AC.

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Re: Alternators, DCDC, and air conditioning

Roland Wiench
In reply to this post by Steve Kobb
Hello Steve,

The best way to show some of these guys that come up with putting a
alternator on a wheel or something, is just test it out with all the
instrumentation.  I did this on my motor test bench, which I can test out
all different types of systems.

Anyway, the alternator is not going to charge the battery while its in use.
That's why in a ICE the alternator is auto turn off with a one wire
alternator or with a two wire alternator, the ignition switch turns off the
alternator while the battery is running the starter.

In using the AC pump to drive the alternator,  What will happen when you
first start up the AC pump and when the alternator gets up to excitation
speed which is about 1200 rpm, the current will loop around and back to the
pump and charges the battery with reducing power until it will slow down
below the alternator excitation rpm.

Then the alternator regulators will drop out and the alternator will stop
charging and than the battery voltage now being higher than the alternator
voltage will start to run up the AC again.  It will began to short cycle on
you which will finally discharge the battery.

Roland


----- Original Message -----
From: "Steve Kobb" <[hidden email]>
To: <[hidden email]>
Sent: Friday, December 28, 2007 10:55 PM
Subject: [EVDL] Alternators, DCDC, and air conditioning


>
> Help me out here: I'm torn between two competing perspectives on a
> technical
> issue.
>
> First, the background: I'm converting a 2002 S-10. Thirteen Trojan 12v
> batts
> in the bed; 2 Optima Blue Top D31Ms under the hood. Will probably also get
> an Iota 55 Amp DCDC to keep the Blue Tops juiced.
>
> I'm in Houston - and that starts with H - and that stands for HEAT. By
> August, I can barely put my hands on the steering wheel, so a good A/C
> system is much appreciated.
>
> The guy who's setting up my A/C has been doing auto A/C for many years. He
> wants to power the compressor with a small motor, which would be run off
> of
> the Blue Tops.
>
> And now we get to the controversy: He also wants to add an alternator to
> pump energy back into the Blue Tops. He's convinced that some of the
> kinetic
> energy supplied to the small motor can be recovered by an alternator,
> which
> would thus reduce the total amount of energy required by the air
> conditioning system. Not that he thinks he can CREATE new energy; he just
> wants to get some of it back.
>
> My mechanical engineering friend says this is an absurd idea because it
> violates a law of thermodynamics -- I think The Second. The engineer also
> says that no matter how much energy the alternator might recover, the
> device
> won't make up for its own inefficiencies, and therefore is a losing
> proposition. Net net: I'll wind up with worse performance and worse range
> than if I had just run the A/C right off the Optimas with no attempt at
> re-gen.
>
> At this point, I don't know who is more persuasive. My initial attraction
> to
> the alternator idea was simply this: If I have to turn a belt that runs
> the
> small A/C motor, I might as well ask that belt to turn the alternator, as
> well.
>
> But that's not how my M.E. buddy sees it... and he can't believe that I'm
> even giving this alternator idea any serious consideration.
>
> BTW, I've gone through a great many archived EVDL threads on alternators
> and
> DCDC. They're all fascinating... and I STILL don't know which perspective
> to
> believe.
>
> If you've got any helpful comments on this one, fire away.
>
> Thanks.
>
> Steve
>
>
> --
> View this message in context:
> http://www.nabble.com/Alternators%2C-DCDC%2C-and-air-conditioning-tp14535227s25542p14535227.html
> Sent from the Electric Vehicle Discussion List mailing list archive at
> Nabble.com.
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>

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Re: Alternators, DCDC, and air conditioning

gottdi
In reply to this post by Steve Kobb
Steve,

Run the AC off the pack and if you have an AC motor on your EV then  
you have Regen and can regain some inertia energy to put back into  
your pack. That is the best way and regen is for capturing some  
inertia energy anyway. Not the way you wanted to do it.

:  )


On Dec 28, 2007, at 9:55 PM, Steve Kobb wrote:

>
> Help me out here: I'm torn between two competing perspectives on a  
> technical
> issue.
>
> First, the background: I'm converting a 2002 S-10. Thirteen Trojan  
> 12v batts
> in the bed; 2 Optima Blue Top D31Ms under the hood. Will probably  
> also get
> an Iota 55 Amp DCDC to keep the Blue Tops juiced.
>
> I'm in Houston - and that starts with H - and that stands for HEAT. By
> August, I can barely put my hands on the steering wheel, so a good A/C
> system is much appreciated.
>
> The guy who's setting up my A/C has been doing auto A/C for many  
> years. He
> wants to power the compressor with a small motor, which would be  
> run off of
> the Blue Tops.
>
> And now we get to the controversy: He also wants to add an  
> alternator to
> pump energy back into the Blue Tops. He's convinced that some of  
> the kinetic
> energy supplied to the small motor can be recovered by an  
> alternator, which
> would thus reduce the total amount of energy required by the air
> conditioning system. Not that he thinks he can CREATE new energy;  
> he just
> wants to get some of it back.
>
> My mechanical engineering friend says this is an absurd idea  
> because it
> violates a law of thermodynamics -- I think The Second. The  
> engineer also
> says that no matter how much energy the alternator might recover,  
> the device
> won't make up for its own inefficiencies, and therefore is a losing
> proposition. Net net: I'll wind up with worse performance and worse  
> range
> than if I had just run the A/C right off the Optimas with no  
> attempt at
> re-gen.
>
> At this point, I don't know who is more persuasive. My initial  
> attraction to
> the alternator idea was simply this: If I have to turn a belt that  
> runs the
> small A/C motor, I might as well ask that belt to turn the  
> alternator, as
> well.
>
> But that's not how my M.E. buddy sees it... and he can't believe  
> that I'm
> even giving this alternator idea any serious consideration.
>
> BTW, I've gone through a great many archived EVDL threads on  
> alternators and
> DCDC. They're all fascinating... and I STILL don't know which  
> perspective to
> believe.
>
> If you've got any helpful comments on this one, fire away.
>
> Thanks.
>
> Steve
>
>
> --
> View this message in context: http://www.nabble.com/Alternators%2C- 
> DCDC%2C-and-air-conditioning-tp14535227s25542p14535227.html
> Sent from the Electric Vehicle Discussion List mailing list archive  
> at Nabble.com.
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev

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No need to wait any longer. You can now buy one off the shelf. You can still build one too.
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Re: Alternators, DCDC, and air conditioning

John Mogelnicki
Steve,
You can use a Masterflux Air Conditioning unit,
http://www.masterflux.com/products/sierra/  they don't require a separate
motor or to be driven from your main motor.  Victor from Metric Mind sells
these and I can get them too, but check with Victor first as I don't have my
retail set up yet.

For the alternator, you could use belt drive on the back of the DC motor,
then only had the alternator "ON" when slowing down or shifting up, you
might recapture some energy as "regen" for your 12volt accessory battery, it
would also help slow the motor down in between shifts (assuming your using
manual trans and can wire the alternator to switch on). However the time and
money it would take to set this up would outweigh the benefits of a good
DC-DC Converter.  Just depends if you're playing around with ideas or want
to get on the road.

John

On Dec 29, 2007 3:51 AM, <[hidden email]> wrote:

> Steve,
>
> Run the AC off the pack and if you have an AC motor on your EV then
> you have Regen and can regain some inertia energy to put back into
> your pack. That is the best way and regen is for capturing some
> inertia energy anyway. Not the way you wanted to do it.
>
> :  )
>
>
> On Dec 28, 2007, at 9:55 PM, Steve Kobb wrote:
>
> >
> > Help me out here: I'm torn between two competing perspectives on a
> > technical
> > issue.
> >
> > First, the background: I'm converting a 2002 S-10. Thirteen Trojan
> > 12v batts
> > in the bed; 2 Optima Blue Top D31Ms under the hood. Will probably
> > also get
> > an Iota 55 Amp DCDC to keep the Blue Tops juiced.
> >
> > I'm in Houston - and that starts with H - and that stands for HEAT. By
> > August, I can barely put my hands on the steering wheel, so a good A/C
> > system is much appreciated.
> >
> > The guy who's setting up my A/C has been doing auto A/C for many
> > years. He
> > wants to power the compressor with a small motor, which would be
> > run off of
> > the Blue Tops.
> >
> > And now we get to the controversy: He also wants to add an
> > alternator to
> > pump energy back into the Blue Tops. He's convinced that some of
> > the kinetic
> > energy supplied to the small motor can be recovered by an
> > alternator, which
> > would thus reduce the total amount of energy required by the air
> > conditioning system. Not that he thinks he can CREATE new energy;
> > he just
> > wants to get some of it back.
> >
> > My mechanical engineering friend says this is an absurd idea
> > because it
> > violates a law of thermodynamics -- I think The Second. The
> > engineer also
> > says that no matter how much energy the alternator might recover,
> > the device
> > won't make up for its own inefficiencies, and therefore is a losing
> > proposition. Net net: I'll wind up with worse performance and worse
> > range
> > than if I had just run the A/C right off the Optimas with no
> > attempt at
> > re-gen.
> >
> > At this point, I don't know who is more persuasive. My initial
> > attraction to
> > the alternator idea was simply this: If I have to turn a belt that
> > runs the
> > small A/C motor, I might as well ask that belt to turn the
> > alternator, as
> > well.
> >
> > But that's not how my M.E. buddy sees it... and he can't believe
> > that I'm
> > even giving this alternator idea any serious consideration.
> >
> > BTW, I've gone through a great many archived EVDL threads on
> > alternators and
> > DCDC. They're all fascinating... and I STILL don't know which
> > perspective to
> > believe.
> >
> > If you've got any helpful comments on this one, fire away.
> >
> > Thanks.
> >
> > Steve
> >
> >
> > --
> > View this message in context: http://www.nabble.com/Alternators%2C-
> > DCDC%2C-and-air-conditioning-tp14535227s25542p14535227.html
> > Sent from the Electric Vehicle Discussion List mailing list archive
> > at Nabble.com.
> >
> > _______________________________________________
> > For subscription options, see
> > http://lists.sjsu.edu/mailman/listinfo/ev
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>
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Re: Alternators, DCDC, and air conditioning

Dave Brandt
In reply to this post by Steve Kobb
Run the alternator off of the traction motor tailshaft, and switch it
on only when the brakes are pressed (via a relay run off of the brake
switch) for a mild form of regen.  Keep it separate from the AC motor
system (though you can mount them all to the back of the traction
motor).

--- Steve Kobb <[hidden email]> wrote:

>
> Help me out here: I'm torn between two competing perspectives on a
> technical
> issue.
>
> First, the background: I'm converting a 2002 S-10. Thirteen Trojan
> 12v batts
> in the bed; 2 Optima Blue Top D31Ms under the hood. Will probably
> also get
> an Iota 55 Amp DCDC to keep the Blue Tops juiced.
>
> I'm in Houston - and that starts with H - and that stands for HEAT.
> By
> August, I can barely put my hands on the steering wheel, so a good
> A/C
> system is much appreciated.
>
> The guy who's setting up my A/C has been doing auto A/C for many
> years. He
> wants to power the compressor with a small motor, which would be run
> off of
> the Blue Tops.
>
> And now we get to the controversy: He also wants to add an alternator
> to
> pump energy back into the Blue Tops. He's convinced that some of the
> kinetic
> energy supplied to the small motor can be recovered by an alternator,
> which
> would thus reduce the total amount of energy required by the air
> conditioning system. Not that he thinks he can CREATE new energy; he
> just
> wants to get some of it back.
>
> My mechanical engineering friend says this is an absurd idea because
> it
> violates a law of thermodynamics -- I think The Second. The engineer
> also
> says that no matter how much energy the alternator might recover, the
> device
> won't make up for its own inefficiencies, and therefore is a losing
> proposition. Net net: I'll wind up with worse performance and worse
> range
> than if I had just run the A/C right off the Optimas with no attempt
> at
> re-gen.
>
> At this point, I don't know who is more persuasive. My initial
> attraction to
> the alternator idea was simply this: If I have to turn a belt that
> runs the
> small A/C motor, I might as well ask that belt to turn the
> alternator, as
> well.
>
> But that's not how my M.E. buddy sees it... and he can't believe that
> I'm
> even giving this alternator idea any serious consideration.
>
> BTW, I've gone through a great many archived EVDL threads on
> alternators and
> DCDC. They're all fascinating... and I STILL don't know which
> perspective to
> believe.
>
> If you've got any helpful comments on this one, fire away.
>
> Thanks.
>
> Steve
>
>
> --
> View this message in context:
>
http://www.nabble.com/Alternators%2C-DCDC%2C-and-air-conditioning-tp14535227s25542p14535227.html
> Sent from the Electric Vehicle Discussion List mailing list archive
> at Nabble.com.
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>


David Brandt





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Re: Alternators, DCDC, and air conditioning

Peter VanDerWal
In reply to this post by gottdi
>> Help me out here: I'm torn between two competing perspectives on a
>> technical
>> issue.
>>
>> First, the background: I'm converting a 2002 S-10. Thirteen Trojan
>> 12v batts
>> in the bed; 2 Optima Blue Top D31Ms under the hood. Will probably
>> also get
>> an Iota 55 Amp DCDC to keep the Blue Tops juiced.

Wow, what an incredibly bad choice of batteries.  You do realize that
you'll most likely be replacing those batteries in less than a year?  If
you replace them with the same kind, you'll be doing it again in less than
a year.
Plus you're not going to have much range.

You should go with 8V Golf Cart batteries and only have to replace them
every 2-3 years, or (best bang for the buck) 6V Golf Cart batteries and
replace them every 4-5 years.
Assuming, of course, that you don't murder the pack sooner.

You should also use the Yellow Tops instead of the Blue Tops.  Blue tops
are starting batteries and you're not starting anything are you?  Yellow
Tops are deep cycle batteries which is closer to the way these will be
used.

>> The guy who's setting up my A/C has been doing auto A/C for many
>> years. He
>> wants to power the compressor with a small motor, which would be
>> run off of
>> the Blue Tops.

Not a good idea.  You'll get 10 maybe 15 minutes out of those batteries
before they are drained.  And if you stick with the Blue Tops (insead of
YTs) you'll be replacing them in about 3 months.
Use a high voltage motor and run it directly of the traction pack, or
better yet, use a traction motor with dual shafts and run the AC off the
back shaft of the traction motor.

>> And now we get to the controversy: He also wants to add an
>> alternator to
>> pump energy back into the Blue Tops. He's convinced that some of
>> the kinetic energy supplied to the small motor can be recovered by an
>> alternator, which would thus reduce the total amount of energy required
>> by the air

Won't work.  There is no extra eneryg left lying around to recover.  If
you turn of the electrical power to the small motor will it coast for a
while as it gently slows down?  No! It comes to a stop almost imediately
because of the compressor.
Even if you disconnected the compressor and connected the alternator it
would still come to a stop quickly because there is very little energy
stored in the rotating armture of a small motor.

Have you ever ridden a bicycle with a generator on it?  It gets harder to
pedal when the generator is turned on.
The same thing happens here.  Add an alternator and the motor has to work
harder to drive it.  That means it draws more power.
In fact it would increase the load by MORE than it generated (you ME
friend is right)
Instead of getting 10-15 minutes of AC you'd end up with 5-10 minutes worth.

>> conditioning system. Not that he thinks he can CREATE new energy;
>> he just
>> wants to get some of it back.

But the point is there is no energy left to recover.  It is all going into
either friction losses, etc, or being converted (by the compressor) into
cool air.

>>
>> My mechanical engineering friend says this is an absurd idea
>> because it
>> violates a law of thermodynamics -- I think The Second.

Yup, or the third law, depending on how you want to look at it.

>> engineer also
>> says that no matter how much energy the alternator might recover,
>> the device
>> won't make up for its own inefficiencies, and therefore is a losing
>> proposition. Net net: I'll wind up with worse performance and worse
>> range
>> than if I had just run the A/C right off the Optimas with no
>> attempt at re-gen.

Exactly.

>> At this point, I don't know who is more persuasive.

It doesn't matter who is more persuasive, it matters who is right.  Your
ME friend is right and the mechanic is wrong.

>> the alternator idea was simply this: If I have to turn a belt that
>> runs the
>> small A/C motor, I might as well ask that belt to turn the
>> alternator, as well.

Except the belt isn't doing the work, the motor is.  Part of the energy
lost in the system is overcoming belt losses (inherent in bending and
turning the belt), adding another load will increase you belt losses.
Adding the load itself will increase the work load on the motor (so the
motor now has to work harder to overcome BOTH loads, the extra belt losses
and the alternator)
The alternator is maybe 65% efficient, so only about 65% of the work
needed to turn it will get converted back into electricity.  The motor is
maybe 70% efficient, assuming a V-belt, we'll pretend it's 75% efficient
(all indications are that it's less than that).
So in order to produce say 500 watts of electricity:
500 / .65 = 769 watts (energy into the alternator, includes losses)
667 / .75 = 1025 watts (energy into the belt)
889 / .75 = 1367 watts (electrical energy into the motor)

So to get 500 watts out of the alternator, you have to put an additional
1367 watts into the motor.  Net result is a loss of 867 watts, which comes
from your batteries.


>>
>> But that's not how my M.E. buddy sees it... and he can't believe
>> that I'm
>> even giving this alternator idea any serious consideration.

Hopefully you're not...anymore


--
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junk at the end; then you are specifically authorizing me to do whatever I
wish with the message.  By posting the message you agree that your long
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Re: Alternators, DCDC, and air conditioning

Zeke Yewdall
> You should also use the Yellow Tops instead of the Blue Tops.  Blue tops
> are starting batteries and you're not starting anything are you?  Yellow
> Tops are deep cycle batteries which is closer to the way these will be
> used.

Didn't we establish a few months ago on here that the the blue tops
were the same as yellow tops, just with different terminals for marine
use, and the red tops were the starting batteries?

Z

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Re: Alternators, DCDC, and air conditioning

Chuck Homic
Zeke Yewdall wrote:

>>You should also use the Yellow Tops instead of the Blue Tops.  Blue tops
>>are starting batteries and you're not starting anything are you?  Yellow
>>Tops are deep cycle batteries which is closer to the way these will be
>>used.
>>    
>>
>
>Didn't we establish a few months ago on here that the the blue tops
>were the same as yellow tops, just with different terminals for marine
>use, and the red tops were the starting batteries?
>
>  
>
It says so on optima's web site.  Not much discussion necessary. :)

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Re: Alternators, DCDC, and air conditioning

Jeff Shanab
In reply to this post by Steve Kobb
One of the side benefits of not spinning the AC off of the ICE is that
you can use a hermetically sealed compressor. More than just not loosing
freon into the atmosphere, The power required is reduced as the rotary
shaft seals needed to keep the freon in add a lot of drag.

I think the ideal compressor is the one used on the prius, but it needs
special oil and an inverter to drive it.

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Re: Alternators, DCDC, and air conditioning

John Lussmyer
In reply to this post by Zeke Yewdall
Zeke Yewdall wrote:
> Didn't we establish a few months ago on here that the the blue tops
> were the same as yellow tops, just with different terminals for marine
> use, and the red tops were the starting batteries?
>  

Yup, and I will add that Optima's Quality Control seems to have become
Non-Existant.
I've returned 5 of the 13 I recently bought - so far.  STILL waiting for
the last 2 replacements, and there is a reasonable chance that one of
those 2 is bad.
The fun part is that the dealer told me that the returned batteries
"tested good".  I then had to explain the difference between a
quick/cheap/easy Cold Cranking Test (which is what every store does),
versus a "Reserve Capacity" test (which is what matters to an EV user).  
I've been finding Optima's with 40 minute Reserve Capacities. (120
minute rated, 90 minute expected)

I'm quite sure that the reason they aren't getting LOTS of returns is
that most Optima users are just using them as starting batteries (and
stiff power for their over built stereos), and won't even notice a 50%
loss of capacity.

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Re: Alternators, DCDC, and air conditioning

joe-22
In reply to this post by Peter VanDerWal
Peter, the Blue Tops are fine for the 12V supply, if fed by a good DC/DC
converter - I think that is what he intends to do, isn't it?

Joseph H. Strubhar

Web: www.gremcoinc.com

E-mail: [hidden email]
----- Original Message -----
From: "Peter VanDerWal" <[hidden email]>
To: "Electric Vehicle Discussion List" <[hidden email]>
Sent: Saturday, December 29, 2007 8:43 AM
Subject: Re: [EVDL] Alternators, DCDC, and air conditioning


>>> Help me out here: I'm torn between two competing perspectives on a
>>> technical
>>> issue.
>>>
>>> First, the background: I'm converting a 2002 S-10. Thirteen Trojan
>>> 12v batts
>>> in the bed; 2 Optima Blue Top D31Ms under the hood. Will probably
>>> also get
>>> an Iota 55 Amp DCDC to keep the Blue Tops juiced.
>
> Wow, what an incredibly bad choice of batteries.  You do realize that
> you'll most likely be replacing those batteries in less than a year?  If
> you replace them with the same kind, you'll be doing it again in less than
> a year.
> Plus you're not going to have much range.
>
> You should go with 8V Golf Cart batteries and only have to replace them
> every 2-3 years, or (best bang for the buck) 6V Golf Cart batteries and
> replace them every 4-5 years.
> Assuming, of course, that you don't murder the pack sooner.
>
> You should also use the Yellow Tops instead of the Blue Tops.  Blue tops
> are starting batteries and you're not starting anything are you?  Yellow
> Tops are deep cycle batteries which is closer to the way these will be
> used.
>
>>> The guy who's setting up my A/C has been doing auto A/C for many
>>> years. He
>>> wants to power the compressor with a small motor, which would be
>>> run off of
>>> the Blue Tops.
>
> Not a good idea.  You'll get 10 maybe 15 minutes out of those batteries
> before they are drained.  And if you stick with the Blue Tops (insead of
> YTs) you'll be replacing them in about 3 months.
> Use a high voltage motor and run it directly of the traction pack, or
> better yet, use a traction motor with dual shafts and run the AC off the
> back shaft of the traction motor.
>
>>> And now we get to the controversy: He also wants to add an
>>> alternator to
>>> pump energy back into the Blue Tops. He's convinced that some of
>>> the kinetic energy supplied to the small motor can be recovered by an
>>> alternator, which would thus reduce the total amount of energy required
>>> by the air
>
> Won't work.  There is no extra eneryg left lying around to recover.  If
> you turn of the electrical power to the small motor will it coast for a
> while as it gently slows down?  No! It comes to a stop almost imediately
> because of the compressor.
> Even if you disconnected the compressor and connected the alternator it
> would still come to a stop quickly because there is very little energy
> stored in the rotating armture of a small motor.
>
> Have you ever ridden a bicycle with a generator on it?  It gets harder to
> pedal when the generator is turned on.
> The same thing happens here.  Add an alternator and the motor has to work
> harder to drive it.  That means it draws more power.
> In fact it would increase the load by MORE than it generated (you ME
> friend is right)
> Instead of getting 10-15 minutes of AC you'd end up with 5-10 minutes
> worth.
>
>>> conditioning system. Not that he thinks he can CREATE new energy;
>>> he just
>>> wants to get some of it back.
>
> But the point is there is no energy left to recover.  It is all going into
> either friction losses, etc, or being converted (by the compressor) into
> cool air.
>
>>>
>>> My mechanical engineering friend says this is an absurd idea
>>> because it
>>> violates a law of thermodynamics -- I think The Second.
>
> Yup, or the third law, depending on how you want to look at it.
>
>>> engineer also
>>> says that no matter how much energy the alternator might recover,
>>> the device
>>> won't make up for its own inefficiencies, and therefore is a losing
>>> proposition. Net net: I'll wind up with worse performance and worse
>>> range
>>> than if I had just run the A/C right off the Optimas with no
>>> attempt at re-gen.
>
> Exactly.
>
>>> At this point, I don't know who is more persuasive.
>
> It doesn't matter who is more persuasive, it matters who is right.  Your
> ME friend is right and the mechanic is wrong.
>
>>> the alternator idea was simply this: If I have to turn a belt that
>>> runs the
>>> small A/C motor, I might as well ask that belt to turn the
>>> alternator, as well.
>
> Except the belt isn't doing the work, the motor is.  Part of the energy
> lost in the system is overcoming belt losses (inherent in bending and
> turning the belt), adding another load will increase you belt losses.
> Adding the load itself will increase the work load on the motor (so the
> motor now has to work harder to overcome BOTH loads, the extra belt losses
> and the alternator)
> The alternator is maybe 65% efficient, so only about 65% of the work
> needed to turn it will get converted back into electricity.  The motor is
> maybe 70% efficient, assuming a V-belt, we'll pretend it's 75% efficient
> (all indications are that it's less than that).
> So in order to produce say 500 watts of electricity:
> 500 / .65 = 769 watts (energy into the alternator, includes losses)
> 667 / .75 = 1025 watts (energy into the belt)
> 889 / .75 = 1367 watts (electrical energy into the motor)
>
> So to get 500 watts out of the alternator, you have to put an additional
> 1367 watts into the motor.  Net result is a loss of 867 watts, which comes
> from your batteries.
>
>
>>>
>>> But that's not how my M.E. buddy sees it... and he can't believe
>>> that I'm
>>> even giving this alternator idea any serious consideration.
>
> Hopefully you're not...anymore
>
>
> --
> If you send email to me, or the EVDL, that has > 4 lines of legalistic
> junk at the end; then you are specifically authorizing me to do whatever I
> wish with the message.  By posting the message you agree that your long
> legalistic signature is void.
>
> _______________________________________________
> For subscription options, see
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>
>
>
> --
> No virus found in this incoming message.
> Checked by AVG Free Edition.
> Version: 7.5.516 / Virus Database: 269.17.12/1202 - Release Date:
> 12/29/2007 1:27 PM
>

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Bad YTs? (was Re: Alternators, DCDC, and air conditioning

Peter VanDerWal
In reply to this post by John Lussmyer
Hmm, that begs the question..."How are you charging them"?

YTs are somewhat easier to murder than other batteries.

> Yup, and I will add that Optima's Quality Control seems to have become
> Non-Existant.
> I've returned 5 of the 13 I recently bought - so far.  STILL waiting for
> the last 2 replacements, and there is a reasonable chance that one of
> those 2 is bad.
> The fun part is that the dealer told me that the returned batteries
> "tested good".  I then had to explain the difference between a
> quick/cheap/easy Cold Cranking Test (which is what every store does),
> versus a "Reserve Capacity" test (which is what matters to an EV user).
> I've been finding Optima's with 40 minute Reserve Capacities. (120
> minute rated, 90 minute expected)
>
> I'm quite sure that the reason they aren't getting LOTS of returns is
> that most Optima users are just using them as starting batteries (and
> stiff power for their over built stereos), and won't even notice a 50%
> loss of capacity.
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>


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Re: Bad YTs? (was Re: Alternators, DCDC, and air conditioning

John Lussmyer
Peter VanDerWal wrote:
> Hmm, that begs the question..."How are you charging them"?
>
> YTs are somewhat easier to murder than other batteries.
>  

New YT's, using a PFC-40 with a full set of Regs.
The YT's are definitely bad from the factory.

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Re: Alternators, DCDC, and air conditioning

Steve Kobb
In reply to this post by Steve Kobb
My thanks to all for your remarks and suggestions.

It's official: The "Alternator-A/C-ReGen Idea" has been placed in the Round File.

And now, time for a few comments to specific contributors:

-- To Peter: My 12v batts will be the Trojan J185P model -- most often used for floor scrubbers, according to the local master distributor.

I had an interesting conversation with Craig Quentin about these batteries. Craig, who is the Trojan sales support engineer, told me either that the J185 products are made out of the T-105 plates, or plates just like the 105s -- can't remember which. In any event, this big 12v battery seemed sturdy enough for my project. Craig said they were designed to withstand significant abuse from janitorial personnel, who are not noted for meticulous care of their electrical equipment.

I, on the other hand, will be armed with a Misco refractometer, a Russco 156v safety charger, maybe some PowerPulse desulfators, and -- most important -- an intense desire to take care of my investment.

So, "...an incredibly bad choice of batteries"? I really don't think so. Only time will tell, and of course, I'll be happy to report the results on EVDL.

Do I realize that I'll be "...replacing those batteries in less than a year?" Well, anything is possible, but I just don't think that's going to happen.

It IS true that I don't expect to get more than 3 years out of them, however, and I AM concerned about this: If 1 cell goes out in a 12v battery, I might have to throw out a batt with 5 GOOD cells... vs. throwing out a 6v batt with only 2 good cells left. So, in that sense, the 12v strategy is riskier.

On the other hand, 26 T-105s weigh 1612 lbs and take up a lot more room than the 13 J185P batts, weighing in at a total of 1469 lbs.

Anyway, thanks for your observations, Peter. I appreciate what you had to say.

To John Mogelnicki -- Yes, I've considered the Masterflux. In fact, Chris Robison recommended it to me. That might be something that I eventually try, although for now, I want to see if I can make the original equipment work.

And yes, "playing around with ideas" seems a lot less attractive than getting on the road at this point.

Cheers,

Steve Kobb
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Re: Alternators, DCDC, and air conditioning

Peter VanDerWal
> I had an interesting conversation with Craig Quentin about these
> batteries.
> Craig, who is the Trojan sales support engineer, told me either that the
> J185 products are made out of the T-105 plates, or plates just like the
> 105s

Floor scrubbers generally don't draw anywhere near as much current as an
EV does.

If you're set on using them, knock yourself out.
Just remember we had this conversation six months from now.

--
If you send email to me, or the EVDL, that has > 4 lines of legalistic
junk at the end; then you are specifically authorizing me to do whatever I
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Re: Alternators, DCDC, and air conditioning

Victor Tikhonov
In reply to this post by John Mogelnicki
John Mogelnicki wrote:
> Steve,
> You can use a Masterflux Air Conditioning unit,
> http://www.masterflux.com/products/sierra/  they don't require a separate
> motor or to be driven from your main motor.  Victor from Metric Mind sells
> these and I can get them too, but check with Victor first as I don't have my
> retail set up yet.

I'm talking to Masterflux to offer this choice. A/C compressor is
good unit, but the inverter in its current form is not worth
putting into an EV. Too many unneeded features, unprotected, too
large PCB (much unused space on it) and cost twice as much as
compressor. Amy be someone can come up with small 1-2 kW inverter
for these? If interested, reply off-list for details. We all can
benefit from potential good solution.

Victor

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Re: Alternators, DCDC, and air conditioning

emma lloyd
fartp



Sent from the public domain

On Dec 31, 2007, at 8:33 PM, Metric Mind <[hidden email]> wrote:

> John Mogelnicki wrote:
>> Steve,
>> You can use a Masterflux Air Conditioning unit,
>> http://www.masterflux.com/products/sierra/  they don't require a  
>> separate
>> motor or to be driven from your main motor.  Victor from Metric  
>> Mind sells
>> these and I can get them too, but check with Victor first as I  
>> don't have my
>> retail set up yet.
>
> I'm talking to Masterflux to offer this choice. A/C compressor is
> good unit, but the inverter in its current form is not worth
> putting into an EV. Too many unneeded features, unprotected, too
> large PCB (much unused space on it) and cost twice as much as
> compressor. Amy be someone can come up with small 1-2 kW inverter
> for these? If interested, reply off-list for details. We all can
> benefit from potential good solution.
>
> Victor
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev

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Re: Alternators, DCDC, and air conditioning

emma lloyd
In reply to this post by Victor Tikhonov



Sent from the public domain

On Dec 31, 2007, at 8:33 PM, Metric Mind <[hidden email]> wrote:

> John Mogelnicki wrote:
>> Steve,
>> You can use a Masterflux Air Conditioning unit,
>> http://www.masterflux.com/products/sierra/  they don't require a  
>> separate
>> motor or to be driven from your main motor.  Victor from Metric  
>> Mind sells
>> these and I can get them too, but check with Victor first as I  
>> don't have my
>> retail set up yet.
>
> I'm talking to Masterflux to offer this choice. A/C compressor is
> good unit, but the inverter in its current form is not worth
> putting into an EV. Too many unneeded features, unprotected, too
> large PCB (much unused space on it) and cost twice as much as
> compressor. Amy be someone can come up with small 1-2 kW inverter
> for these? If interested, reply off-list for details. We all can
> benefit from potential good solution.
>
> Victor
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev

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