pre-charge resistor?

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pre-charge resistor?

Mike Golub-2
Is there a circuit out there that would allow the pre-charge resistor
to be off.
And when the key is put in it allows the pre-charge resistor to turn on?

And then only allows the car to drive when enough pre-charge is done.

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Re: pre-charge resistor?

AMPhibian
Here is an extensive post on the subject:  http://www.diyelectriccar.com/forums/showthread.php?t=25318

m gol wrote
Is there a circuit out there that would allow the pre-charge resistor
to be off.
And when the key is put in it allows the pre-charge resistor to turn on?

And then only allows the car to drive when enough pre-charge is done.

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Re: pre-charge resistor?

Lee Hart
In reply to this post by Mike Golub-2
On 5/28/2011 5:59 PM, m gol wrote:
> Is there a circuit out there that would allow the pre-charge resistor
> to be off. And when the key is put in it allows the pre-charge resistor to turn on?

Sure. The standard way to do it is with a relay. Its 12v coil is powered
when you turn the key on. Its contacts connect the precharge resistor
across the main contactor.

> And then only allows the car to drive when enough pre-charge is done.

That is a little trickier. When charging a big bank of capacitors with a
resistor, there is a "time constant" T = R x C (T in seconds, R in ohms,
C in farads). Every T seconds, the voltage moves 63% of the way to the
final voltage. Example: Your precharge resistor R is 250 ohms, your
controller's capacitors total 40,000uF = 0.04 farads, and your pack
voltage is 120vdc. Then:

  - T = 250 ohms x 0.04 farad = 10 second time constant
  - at 10 sec, controller goes from 0v to 75.6v
  - at 20 sec, controller goes from 75.6v to 103.6v
  - at 30 sec, controller goes from 103.6v to 114v

It never actually gets to 120v, but keeps getting closer. At some point
you need to decide "that's close enough". When you're 90% of the way
there, the peak current when the main contactor closes is 10% of what it
would have been without precharging; that is usually good enough.

Most people don't want to wait a long time for precharge. A lower value
precharge resistor charges faster, but also gets bigger and hotter. The
250 ohm resistor in the above example dissipates P = V^2/R = 57.6 watts
-- you need at least a 20w resistor to survive 30 seconds or so at 3x
its rated power. If you wanted to cut the precharge time 10:1 (T = 3 sec
instead of 30 sec), now the peak power is 576 watts and you need
something like 75 watt resistor to survive a few seconds!

The precharge resistor gets *very* hot and can even burn out or start a
fire if for some reason the controller won't precharge. For example, if
your foot it already on the throttle when you try to precharge, or if
you have some other load like your DC/DC converter also connected.

This is why I like to use light bulbs as precharge resistors. It's easy
to get a 75 watt light bulb. They precharge faster than a resistor,
because a light bulb's cold resistance is about 1/10 its hot resistance.
If the controller does fail to precharge, the light simply lights up at
full brightness.

For an automatic system to detect when the controller has precharged:
You can make this as complicated as you like, with a microcomputer
monitoring the voltage, etc.

I prefer something simple. I connect a relay coil across the controller
input, with enough resistors and/or zener diode so the relay pulls in
when the voltage reaches about 90% of the pack voltage. The relay's
contacts close, which enables the main contactor so you can drive.
--
Lee A. Hart | Ring the bells that still can ring
814 8th Ave N | Forget the perfect offering
Sartell MN 56377 | There is a crack in everything
leeahart earthlink.net | That's how the light gets in -- Leonard Cohen

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Re: pre-charge resistor?

Danpatgal
I have finally finished all the wiring on my new and improved Lectric Leopard - now using lithium! (38x130ah CALB cells - 120v nominal).  While I was at it I included new instrumentation, a BMS, and some additional features that were not in the car when I got it like an inertia switch, mid-pack fuse, and pre-charge resistor.  According to the Curtis manual, the precharge resistor goes accross the contacts of the main contactor, so I got a one (750ohm) from KTA and wired it in.

Last night (one of those late night - don't do anything stupid, but yes I want to at least power on and see if there are any problems) I filpped the main circuit braker closed, and thankfully nothing blew up.  I measured the voltage across the contacts: it was something like 68 volts.  Before I had the precharge resistor in place I measured FULL pack voltage across the contacts.  (In retrospect I should have known why, but, well - I did say it was late, right?).  After a few minutes I smelled the heated incandescent bulb kind of smell.  Hmm, what is that?  Finally, I measured from B- to the "closed" side of the main contactor and I measured something like 57 volts.  The math wiz that I am ;), I realized that 57 + 68 was about what I should see for full pack voltage ... jeez, ooh, now I understand.

Then I read this thread (again), and the DIY thread here:

  http://www.diyelectriccar.com/forums/showthread.php?t=25419

(These descriptions always make more sense to me AFTER I've tried it myself).

So, I have two questions:

1.- Is there any negative impact to having this low current path "on" all the time?  I assume that once the controller capacitors are charged and the DC-DC has charged the 12v battery (if necessary), it's pulling a very low level (a few watts ??) of power.

2.- In the DIY thread, the author references a "Step-Start" device - is that something available for purchase?

or ... is there a contactor that already has a precharge circuit built in?  It seems like this Gigavac unit does:

  www.evsource.com/tls_gigavac.php

Does anybody have experience with it ??

Thanks - Dan

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Re: pre-charge resistor?

Lee Hart
On 10/1/2012 9:12 AM, Danpatgal wrote:
> I have finally finished all the wiring on my new and improved Lectric Leopard
> - now using lithium!

Congratulations! I also have a Lectric Leopard. Its been reconverted, so
nothing of US Electricar's handiwork remains. But it's still on lead (no
dough for lithium).

> pre-charge resistor... 750ohms... 68 volts across the main contactor...
> After a few minutes I smelled the heated incandescent bulb kind of smell.

Well, you have 68 volts across a 750 ohm resistor. Power = V^2 / R =
68v^2 / 750ohms = 4624 / 750 = 6.165 watts. What wattage is your
precharge resistor? 6 watts is probably a good percentage of its maximum
wattage rating. It gets hot!

> Then I read this thread (again), and the DIY thread here:
> http://www.diyelectriccar.com/forums/showthread.php?t=25419
> So, I have two questions:
>
> 1.- Is there any negative impact to having this low current path "on" all
> the time?

Yes.

1. It slowly runs your pack dead. In your case, the precharge
    resistor current is I = V / R = 68v / 750ohms = 0.09 amps.
    This load alone will run your 130ah pack dead in about
    130ah / 0.09a = 1444 hours (about 2 months).

2. Your controller is precharged all the time. Even with the
    key off, if you step on the throttle, the motor will run
    momentarily on the charge in the controller's capacitors.

> I assume that once the controller capacitors are charged and the
> DC-DC has charged the 12v battery (if necessary), it's pulling a very low
> level (a few watts ??) of power.

It's pulling full pack voltage 120v x 0.09 amps = 10.8 watts all the
time. 6 watts is burned up by the precharge resistor, the rest is
powering the controller itself.

> 2.- In the DIY thread, the author references a "Step-Start" device - is that
> something available for purchase?

I think he started that thread to sell his magic device. :-) However,
all you really need is a simple relay, with a 12vdc coil, and a
normally-open contact that can switch pack voltage at the current your
precharge resistor draws.

Wire its 12v coil to turn on when you turn the key "on". Wire its
contacts in series with the precharge resistor. When the key is off, the
relay is off, and the precharge resistor is off. When you turn the key
on, wait a few seconds for the resistor to precharge the controller then
drive.

The main contactor's coil is normally wired through the switch on the
potbox. Thus it won't pull in until you press the throttle, which will
(usually) be many seconds after you turned the key on. A typical
scenario is to get in the car, turn the key "on", put on your seatbelt,
adjust the mirror, shift into reverse, etc. *Then* press the throttle.

A nice improvement is to wire a little neon indicator lamp from
controller B+ to B-. Mount it on the dash so you can see it, and label
it "Ready". When it's lit, the controller is precharged. This way, you
can turn on the key and wait for this indicator to light.

A further improvement is to add a second relay, wired the same place as
the "Ready" indicator. This relay is rated for pack voltage, and pulls
in when the controller has precharged. When it pulls in, its contacts
enable the main contactor coil. This automatically provides the
precharge delay, so even if someone presses the throttle and *then*
turns on the key (which would provide no precharge), this second relay
keeps the main contactor off until the controller has precharged.

Note 1:

0.09a is a pretty large precharge current. The Curtis controller usually
only draws 20ma, so I'll bet you also have your DC/DC converter wired
between controller B+ and B-. It's probably drawing 0.07a out of that
0.09a total.

The DC/DC should have its own precharge resistor across its power switch
(or relay, if you want it switched on/off with the key).

Note 2: 750 ohms is a pretty large precharge resistance. It makes for
slow precharging, and doesn't reduce the voltage across the main
contactor all that much. Instead of 68v, you want to see something under
10 volts across the main contactor when it closes.

I prefer to use ordinary 120v light bulbs as my precharge "resistor".
They are cheap, available, precharge quicker and more fully, and won't
overheat and fail if some fault condition keeps them in the circuit
longer than expected.

> or ... is there a contactor that already has a precharge circuit built in?
> It seems like this Gigavac unit does:
>    www.evsource.com/tls_gigavac.php

No, it does not have built-in precharge. It *does* have built-in
economizer circuit for its *coil*, though. A coil economizer reduces the
current that the coil draws to hold it pulled in (saving 12vdc power).
Here is my example:

http://www.sunrise-ev.com/LeesEVs.htm (EV circuit #3)

I don't know of a contactor with built-in precharge; but lots of people
make controllers and other devices with external precharge circuits.
--
Anyone can make the simple complicated. Creativity is making the
complicated simple. -- Charles Mingus
--
Lee A. Hart http://www.sunrise-ev.com/LeesEVs [hidden email]

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Re: pre-charge resistor?

Danpatgal
Thanks Lee ...

Lee Hart wrote
I also have a Lectric Leopard. Its been reconverted, so nothing of US Electricar's handiwork remains. But it's still on lead (no dough for lithium).
Nice.  Mine is little more than a cleaner 30 year old Renault LeCar shell - especially now that I've put in the lithium.  (And that's making it sound nice.)  But small and light makes for a good EV.
Lee Hart wrote
What wattage is your precharge resistor?
25w - it did get hot, but well within the limits.  I could do a lightbulb, that just seems kind of bulky ... maybe I'll try to find lower value ohm (higher wattage) resistor.

I have a very simple setup without a throttle contactor ... the key turns on the main contactor and away I go.  Oblivious, I ran this way without a precharge resistor for a year.  So I'd have to add a relay to limit in-rush current.   ... I'm thinking about how to do that, maybe my BMS can help, since I feed the ignition signal to it, and then it turns on the main contactor.  Maybe I could split that ignition 12v to a relay that powers the precharge and program the BMS to wait 10 seconds before closing the main contactor ....

Thanks for the help ....  
Dan  


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Re: pre-charge resistor?

Cor van de Water
Hi Dan,
A manual way is to close the pre-charge when you first turn
the ignition ON and close (and hold) the main contactor
when you turn the ignition to "start".
If the pre-charge is done in about 1 second then this is a
rather natural flow of things - turn the key on, wait a sec
and then "start" the car.

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [hidden email] Private: http://www.cvandewater.info
Skype: cor_van_de_water Tel: +1 408 383 7626


-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of Danpatgal
Sent: Monday, October 01, 2012 2:14 PM
To: [hidden email]
Subject: Re: [EVDL] pre-charge resistor?

Thanks Lee ...


Lee Hart wrote
> I also have a Lectric Leopard. Its been reconverted, so nothing of US
> Electricar's handiwork remains. But it's still on lead (no dough for
> lithium).

Nice.  Mine is little more than a cleaner 30 year old Renault LeCar
shell -
especially now that I've put in the lithium.  (And that's making it
sound
nice.)  But small and light makes for a good EV.

Lee Hart wrote
> What wattage is your precharge resistor?

25w - it did get hot, but well within the limits.  I could do a
lightbulb,
that just seems kind of bulky ... maybe I'll try to find lower value ohm
(higher wattage) resistor.

I have a very simple setup without a throttle contactor ... the key
turns on
the main contactor and away I go.  Oblivious, I ran this way without a
precharge resistor for a year.  So I'd have to add a relay to limit
in-rush
current.   ... I'm thinking about how to do that, maybe my BMS can help,
since I feed the ignition signal to it, and then it turns on the main
contactor.  Maybe I could split that ignition 12v to a relay that powers
the
precharge and program the BMS to wait 10 seconds before closing the main
contactor ....

Thanks for the help ....  
Dan  






-----
Dan Gallagher
http://www.evalbum.com/3854

--
View this message in context:
http://electric-vehicle-discussion-list.413529.n4.nabble.com/pre-charge-
resistor-tp3558165p4658367.html
Sent from the Electric Vehicle Discussion List mailing list archive at
Nabble.com.

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Re: pre-charge resistor?

Elithion
In reply to this post by Mike Golub-2
Mike Golub-2 wrote
Is there a circuit out there that would allow the pre-charge resistor
to be off.
And when the key is put in it allows the pre-charge resistor to turn on?
Even better: all about precharge circuits and components: http://liionbms.com/php/precharge.php
Davide Andrea
Elithion
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Re: pre-charge resistor?

Charles Eldridge
In reply to this post by Danpatgal
I recently installed a pre-charge resistor across the contacts of the
main contactor while using it with
a Curtis 1231 controller.  I could not tell any difference between
operation with and without the
resistor.  More recently, I've installed a 'Cougar' controller by
PaulandSabrinasEVstuff.  This controller
has a separate output to energize the contactor coil and a
configurable precharge timer.  I use 3 seconds for this timer.  I have
a pack volt meter, and now I see that the volt meter slowly approaches
pack voltage during those 3 seconds.  It doesn't get all the way there
before the 3 seconds are up, though.  When the 3 seconds are up, then
the main contactor contacts close, and the volt meter shows the full
pack voltage.

I had read on this list earlier (or maybe elsewhere) that the
precharge resistor promotes a longer life for the controller's power
electronics.  In other words, it's better to leak the current in and
have the voltage rise slowly than to 'slam' the power electronics with
the full pack voltage all at once.

If I were to measure voltage across those contacts, I would see the
pack voltage initially. But this voltage would drop as the
controller's capacitors charge up.

Bottom line:  seems OK that you see pack voltage across the contacts,
initially at least.



On Mon, Oct 1, 2012 at 10:12 AM, Danpatgal <[hidden email]> wrote:

> I have finally finished all the wiring on my new and improved Lectric Leopard
> - now using lithium! (38x130ah CALB cells - 120v nominal).  While I was at
> it I included new instrumentation, a BMS, and some additional features that
> were not in the car when I got it like an inertia switch, mid-pack fuse, and
> pre-charge resistor.  According to the Curtis manual, the precharge resistor
> goes accross the contacts of the main contactor, so I got a one (750ohm)
> from KTA and wired it in.
>
> Last night (one of those late night - don't do anything stupid, but yes I
> want to at least power on and see if there are any problems) I filpped the
> main circuit braker closed, and thankfully nothing blew up.  I measured the
> voltage across the contacts: it was something like 68 volts.  Before I had
> the precharge resistor in place I measured FULL pack voltage across the
> contacts.  (In retrospect I should have known why, but, well - I did say it
> was late, right?).  After a few minutes I smelled the heated incandescent
> bulb kind of smell.  Hmm, what is that?  Finally, I measured from B- to the
> "closed" side of the main contactor and I measured something like 57 volts.
> The math wiz that I am ;), I realized that 57 + 68 was about what I should
> see for full pack voltage ... jeez, ooh, now I understand.
>
> Then I read this thread (again), and the DIY thread here:
>
>   http://www.diyelectriccar.com/forums/showthread.php?t=25419
>
> (These descriptions always make more sense to me AFTER I've tried it
> myself).
>
> So, I have two questions:
>
> 1.- Is there any negative impact to having this low current path "on" all
> the time?  I assume that once the controller capacitors are charged and the
> DC-DC has charged the 12v battery (if necessary), it's pulling a very low
> level (a few watts ??) of power.
>
> 2.- In the DIY thread, the author references a "Step-Start" device - is that
> something available for purchase?
>
> or ... is there a contactor that already has a precharge circuit built in?
> It seems like this Gigavac unit does:
>
>   www.evsource.com/tls_gigavac.php
>
> Does anybody have experience with it ??
>
> Thanks - Dan
>
>
>
>
>
> -----
> Dan Gallagher
> http://www.evalbum.com/3854
>
> --
> View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/pre-charge-resistor-tp3558165p4658356.html
> Sent from the Electric Vehicle Discussion List mailing list archive at Nabble.com.
>
> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
> | Please take those discussions elsewhere.  Thanks.
> |
> | REPLYING: address your message to [hidden email] only.
> | Multiple-address or CCed messages may be rejected.
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Re: pre-charge resistor?

Mike Nickerson
In reply to this post by Lee Hart
If the pre-charge resistor is always keeping the controller input charged,
it is also keeping the motor inputs at pack voltage.  This is enough to feel
a shock if you put your arm across the motor terminals.  Yes, that is the
voice of experience.  Make sure you disconnect power and give the controller
caps time to dissipate.  It can take 5 minutes or more.  Check with a meter.

Expounding on Lee's comments about the DC-DC converter:  If it is hooked up
after the pre-charge resistor and not separately switched, two things will
happen.  First, once the controller charges high enough, it will activate
the input of the DC-DC and turn it on.  The DC-DC will then drain the charge
and cycle off again.  This can cycle the DC-DC converter 2-3 times per
minute.

Second, when the converter drains the charge, it prevents the pre-charge
resistor from doing its job and protecting the controller as well.

This also adds to the power loss from the pack and the heating of the
resistor.

Mike

> -----Original Message-----
> From: [hidden email] [mailto:[hidden email]] On
> Behalf Of Lee Hart
> Sent: Monday, October 01, 2012 12:33 PM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] pre-charge resistor?
>
> On 10/1/2012 9:12 AM, Danpatgal wrote:
> > I have finally finished all the wiring on my new and improved Lectric
> > Leopard
> > - now using lithium!
>
> Congratulations! I also have a Lectric Leopard. Its been reconverted, so
> nothing of US Electricar's handiwork remains. But it's still on lead (no
dough
> for lithium).
>
> > pre-charge resistor... 750ohms... 68 volts across the main contactor...
> > After a few minutes I smelled the heated incandescent bulb kind of
smell.

>
> Well, you have 68 volts across a 750 ohm resistor. Power = V^2 / R =
> 68v^2 / 750ohms = 4624 / 750 = 6.165 watts. What wattage is your precharge
> resistor? 6 watts is probably a good percentage of its maximum wattage
> rating. It gets hot!
>
> > Then I read this thread (again), and the DIY thread here:
> > http://www.diyelectriccar.com/forums/showthread.php?t=25419
> > So, I have two questions:
> >
> > 1.- Is there any negative impact to having this low current path "on"
> > all the time?
>
> Yes.
>
> 1. It slowly runs your pack dead. In your case, the precharge
>     resistor current is I = V / R = 68v / 750ohms = 0.09 amps.
>     This load alone will run your 130ah pack dead in about
>     130ah / 0.09a = 1444 hours (about 2 months).
>
> 2. Your controller is precharged all the time. Even with the
>     key off, if you step on the throttle, the motor will run
>     momentarily on the charge in the controller's capacitors.
>
> > I assume that once the controller capacitors are charged and the DC-DC
> > has charged the 12v battery (if necessary), it's pulling a very low
> > level (a few watts ??) of power.
>
> It's pulling full pack voltage 120v x 0.09 amps = 10.8 watts all the time.
6 watts
> is burned up by the precharge resistor, the rest is powering the
controller
> itself.
>
> > 2.- In the DIY thread, the author references a "Step-Start" device -
> > is that something available for purchase?
>
> I think he started that thread to sell his magic device. :-) However, all
you
> really need is a simple relay, with a 12vdc coil, and a normally-open
contact
> that can switch pack voltage at the current your precharge resistor draws.
>
> Wire its 12v coil to turn on when you turn the key "on". Wire its contacts
in
> series with the precharge resistor. When the key is off, the relay is off,
and
> the precharge resistor is off. When you turn the key on, wait a few
seconds
> for the resistor to precharge the controller then drive.
>
> The main contactor's coil is normally wired through the switch on the
potbox.
> Thus it won't pull in until you press the throttle, which will
> (usually) be many seconds after you turned the key on. A typical scenario
is
> to get in the car, turn the key "on", put on your seatbelt, adjust the
mirror,
> shift into reverse, etc. *Then* press the throttle.
>
> A nice improvement is to wire a little neon indicator lamp from controller
B+
> to B-. Mount it on the dash so you can see it, and label it "Ready". When
it's
> lit, the controller is precharged. This way, you can turn on the key and
wait
> for this indicator to light.
>
> A further improvement is to add a second relay, wired the same place as
the
> "Ready" indicator. This relay is rated for pack voltage, and pulls in when
the
> controller has precharged. When it pulls in, its contacts enable the main
> contactor coil. This automatically provides the precharge delay, so even
if
> someone presses the throttle and *then* turns on the key (which would
> provide no precharge), this second relay keeps the main contactor off
until
> the controller has precharged.
>
> Note 1:
>
> 0.09a is a pretty large precharge current. The Curtis controller usually
only
> draws 20ma, so I'll bet you also have your DC/DC converter wired between
> controller B+ and B-. It's probably drawing 0.07a out of that 0.09a total.
>
> The DC/DC should have its own precharge resistor across its power switch
(or

> relay, if you want it switched on/off with the key).
>
> Note 2: 750 ohms is a pretty large precharge resistance. It makes for slow
> precharging, and doesn't reduce the voltage across the main contactor all
> that much. Instead of 68v, you want to see something under
> 10 volts across the main contactor when it closes.
>
> I prefer to use ordinary 120v light bulbs as my precharge "resistor".
> They are cheap, available, precharge quicker and more fully, and won't
> overheat and fail if some fault condition keeps them in the circuit longer
than
> expected.
>
> > or ... is there a contactor that already has a precharge circuit built
in?
> > It seems like this Gigavac unit does:
> >    www.evsource.com/tls_gigavac.php
>
> No, it does not have built-in precharge. It *does* have built-in
economizer
> circuit for its *coil*, though. A coil economizer reduces the current that
the
> coil draws to hold it pulled in (saving 12vdc power).
> Here is my example:
>
> http://www.sunrise-ev.com/LeesEVs.htm (EV circuit #3)
>
> I don't know of a contactor with built-in precharge; but lots of people
make

> controllers and other devices with external precharge circuits.
> --
> Anyone can make the simple complicated. Creativity is making the
> complicated simple. -- Charles Mingus
> --
> Lee A. Hart http://www.sunrise-ev.com/LeesEVs [hidden email]
>
> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
> | Please take those discussions elsewhere.  Thanks.
> |
> | REPLYING: address your message to [hidden email] only.
> | Multiple-address or CCed messages may be rejected.
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Re: pre-charge resistor?

Lee Hart
In reply to this post by Elithion
On 10/1/2012 7:47 PM, Elithion wrote:
> Even better: all about precharge circuits and components:
> http://liionbms.com/php/precharge.php

A nice write-up, Elithion. A couple things I could add:

1. An EV's main contactor needs the ability to break a fault
    current that is many times higher than normal. For example,
    if the motor or controllers shorts, the contactor is the
    backup system to stop the excitement!

    You should have a fuse or circuit breaker as well. But these
    won't necessarily open, because while the fault current is
    high, it may not be *that* high. For example, a series motor
    controller can fail "on", and the motor will accelerate to
    a dangerous RPM without a high battery current flowing.

2. Relay contacts bounce. Therefore, the precharge relay's
    contacts *will* open with full precharge current flowing.
    With a 120vdc pack and 10 ohm resistor as in your example,
    the precharge contact switches I = 120v/10ohm = 12 amps.
    It takes a pretty substantial relay to survive this for long.

    It's a much better "deal" to put an RC snubber across the
    precharge relay's contacts. This greatly reduces arcing,
    allowing a smaller relay for a given life.

3. A fixed precharge delay has drawbacks. Controllers have a
    wide range of input capacitor sizes and we don't know what
    value precharge resistor a customer will use, so the time
    delay needed to adequately precharge is unknown. It's better
    to provide a light to indicate when the controller has
    precharged (neons are good). It's better still to have a
    relay or other voltage sensor that won't turn on the main
    contactor until the controller has precharged.

4. I like light bulbs for precharging because they precharge
    fast, provide a visual indication, and won't fail if the
    the controller fails to precharge (the light just stays lit).
    A precharge resistor is likely to burn up if the controller
    won't precharge for some reason!
--
Failure is only the opportunity to begin again more intelligently.
         -- Henry Ford
--
Lee A. Hart http://www.sunrise-ev.com/LeesEVs [hidden email]

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Re: pre-charge resistor?

Lee Hart
On 10/2/2012 10:32 PM, David Nelson wrote:
> Is the RC subber wired up like so? C1--R--C--C2 where C1 and C2 are
> the opposite sides of the relay contacts?

Yes.

The snubber R and C are in series, and this pair is wired across the
contact to be protected.

> How are the sizes of the R and C determined?

The "correct" values can be calculated or measured: But most people
don't have the data or knowledge to do it, and don't have the equipment
to measure it, and (most importantly) don't feel like taking the time to
do it. :-(

Luckily, the values are not at all critical. Anything even close helps a
lot. So just about everyone (including me) estimate the values with
rules of thumb, and use whatever parts are handy. :-)

You can buy pre-made RC snubbers, or steal one out of a junked light
dimmer (they all have them across the triac). The capacitor is typically
0.047uf to 0.22uf and rated for the voltage that appears across the
contact. The resistor is 10-100 ohms, and rated for at least 1/2 watt.
These are reasonable values for switching a load of about 100-200v and
1-10 amps.

The basic idea is that when the contact is closed, the capacitor is
discharged. When the contact opens, the capacitor holds down the voltage
across the contact while it charges. There should be enough capacitance
to keep the contact voltage low enough and long enough to extinguish or
at least minimize the arc.

The resistor limits the current the contact has to carry when it closes
to discharge the capacitor, and also forms a damped L-R-C circuit in
case the load is inductive so it won't ring and generate RFI.
--
A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away.
        -- Antoine de Saint ExupĂ©ry
--
Lee A. Hart http://www.sunrise-ev.com/LeesEVs [hidden email]

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Re: pre-charge resistor?

Dennis Miles
In reply to this post by Lee Hart
A lot of interesting discussion and use of Ohm's law in this series of
posts but the voltage of the pack varies in different paragraphs, in the
first couple of posts so I have been totally confused and I would ask, if
you were my students, you to do the assignment "Explain implementing
'Pre-charging' ?" again to demonstrate competence.
Any piece of EV equipment that is often disconnected and reconnected from
the pack and has a large quantity of capacitive filtering in its input
circuitry benefits from "Pre-charging." The simplest and most reliable
pre-charge implementation is a suitable relay engaged a few seconds before
the main power contacter is engaged. The pre-charge relay supplies power
from the pack only to the controller, feeding thru a current limiter to
reduce initial capacitor charge -up, the current limiter can be a "Power
resistor" of 150 to 750 ohms, a wattage of 25 watts or more is used because
their size makes them more immune to vibration cracking. An alternative is
one or two light bulbs at 40 to 60 watts and rated for vibration service
like used with lights in ceiling fans in the home. Use one bulb for each
100 to 150 volts of pack voltage, in series! Note that one should not
switch other loads like the DC/DC on and off with the Controller and the
capacitive filtering in the input circuit of the DC/DC is much smaller in
capacitance and often includes an inductor so a pre-charge circuit is less
necessary.
Regards,
*     Dennis *(EVprofessor.*sm*)* Miles*
  *(863)944-9913* (phone noon to midnight E.S.T.)
*    reply to [hidden email]*
*        EVprofessor.sm is a Service Mark of:*
*           Electric Vehicle Technical Institute inc.*

On Mon, Oct 1, 2012 at 2:32 PM, Lee Hart <[hidden email]> wrote:

> On 10/1/2012 9:12 AM, Danpatgal wrote:
> > I have finally finished all the wiring on my new and improved Lectric
> Leopard
> > - now using lithium!
>
> Congratulations! I also have a Lectric Leopard. Its been reconverted, so
> nothing of US Electricar's handiwork remains. But it's still on lead (no
> dough for lithium).
>
> > pre-charge resistor... 750ohms... 68 volts across the main contactor...
> > After a few minutes I smelled the heated incandescent bulb kind of smell.
>
> Well, you have 68 volts across a 750 ohm resistor. Power = V^2 / R =
> 68v^2 / 750ohms = 4624 / 750 = 6.165 watts. What wattage is your
> precharge resistor? 6 watts is probably a good percentage of its maximum
> wattage rating. It gets hot!
>
> > Then I read this thread (again), and the DIY thread here:
> > http://www.diyelectriccar.com/forums/showthread.php?t=25419
> > So, I have two questions:
> >
> > 1.- Is there any negative impact to having this low current path "on" all
> > the time?
>
> Yes.
>
> 1. It slowly runs your pack dead. In your case, the precharge
>     resistor current is I = V / R = 68v / 750ohms = 0.09 amps.
>     This load alone will run your 130ah pack dead in about
>     130ah / 0.09a = 1444 hours (about 2 months).
>
> 2. Your controller is precharged all the time. Even with the
>     key off, if you step on the throttle, the motor will run
>     momentarily on the charge in the controller's capacitors.
>
> > I assume that once the controller capacitors are charged and the
> > DC-DC has charged the 12v battery (if necessary), it's pulling a very low
> > level (a few watts ??) of power.
>
> It's pulling full pack voltage 120v x 0.09 amps = 10.8 watts all the
> time. 6 watts is burned up by the precharge resistor, the rest is
> powering the controller itself.
>
> > 2.- In the DIY thread, the author references a "Step-Start" device - is
> that
> > something available for purchase?
>
> I think he started that thread to sell his magic device. :-) However,
> all you really need is a simple relay, with a 12vdc coil, and a
> normally-open contact that can switch pack voltage at the current your
> precharge resistor draws.
>
> Wire its 12v coil to turn on when you turn the key "on". Wire its
> contacts in series with the precharge resistor. When the key is off, the
> relay is off, and the precharge resistor is off. When you turn the key
> on, wait a few seconds for the resistor to precharge the controller then
> drive.
>
> The main contactor's coil is normally wired through the switch on the
> potbox. Thus it won't pull in until you press the throttle, which will
> (usually) be many seconds after you turned the key on. A typical
> scenario is to get in the car, turn the key "on", put on your seatbelt,
> adjust the mirror, shift into reverse, etc. *Then* press the throttle.
>
> A nice improvement is to wire a little neon indicator lamp from
> controller B+ to B-. Mount it on the dash so you can see it, and label
> it "Ready". When it's lit, the controller is precharged. This way, you
> can turn on the key and wait for this indicator to light.
>
> A further improvement is to add a second relay, wired the same place as
> the "Ready" indicator. This relay is rated for pack voltage, and pulls
> in when the controller has precharged. When it pulls in, its contacts
> enable the main contactor coil. This automatically provides the
> precharge delay, so even if someone presses the throttle and *then*
> turns on the key (which would provide no precharge), this second relay
> keeps the main contactor off until the controller has precharged.
>
> Note 1:
>
> 0.09a is a pretty large precharge current. The Curtis controller usually
> only draws 20ma, so I'll bet you also have your DC/DC converter wired
> between controller B+ and B-. It's probably drawing 0.07a out of that
> 0.09a total.
>
> The DC/DC should have its own precharge resistor across its power switch
> (or relay, if you want it switched on/off with the key).
>
> Note 2: 750 ohms is a pretty large precharge resistance. It makes for
> slow precharging, and doesn't reduce the voltage across the main
> contactor all that much. Instead of 68v, you want to see something under
> 10 volts across the main contactor when it closes.
>
> I prefer to use ordinary 120v light bulbs as my precharge "resistor".
> They are cheap, available, precharge quicker and more fully, and won't
> overheat and fail if some fault condition keeps them in the circuit
> longer than expected.
>
> > or ... is there a contactor that already has a precharge circuit built
> in?
> > It seems like this Gigavac unit does:
> >    www.evsource.com/tls_gigavac.php
>
> No, it does not have built-in precharge. It *does* have built-in
> economizer circuit for its *coil*, though. A coil economizer reduces the
> current that the coil draws to hold it pulled in (saving 12vdc power).
> Here is my example:
>
> http://www.sunrise-ev.com/LeesEVs.htm (EV circuit #3)
>
> I don't know of a contactor with built-in precharge; but lots of people
> make controllers and other devices with external precharge circuits.
> --
> Anyone can make the simple complicated. Creativity is making the
> complicated simple. -- Charles Mingus
> --
> Lee A. Hart http://www.sunrise-ev.com/LeesEVs [hidden email]
>
> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
> | Please take those discussions elsewhere.  Thanks.
> |
> | REPLYING: address your message to [hidden email] only.
> | Multiple-address or CCed messages may be rejected.
> | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> | OTHER HELP: http://evdl.org/help/
> | CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
>



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|
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Re: pre-charge resistor?

Mike Nickerson
Hi Dennis,

The other option with loads such as DC-DC converters is an inrush limiting
resistor.  This is a resistor with a negative temperature coefficient.  When
cold, it has a fairly high resistance (10 ohms or so).  When hot, it has a
very small resistance to conduct the current.

Ideally, the inrush limiter is sized (maximum value of resistance) to ensure
the inrush current is within the maximum input current specification of the
device to be protected.  If the pack voltage is 150V and the cold resistance
is 10 ohms, you will have 15A flow into the DC-DC converter initially.  

The inrush limiter (current capacity) must also be sized to support the
maximum current draw of the converter.  This is an important consideration
because the power dissipation in the inrush limiter will be I*I *R where I
is the current draw of the converter and R is the hot resistance of the
inrush limiter.

Of course, that is why inrush limiters aren't used for the main contactor.
Inrush limiters couldn't take the hundreds of amps used on the main traction
circuit.  They are, however, a good solution for accessories such as the
DC-DC converter.

I completely agree that you don't want these accessories switched by the
main contactor with a pre-charge resistor.  They can be on the switched side
of the contactor, but they should have their own (additional) switch or
contactor.  Otherwise, they draw down the controller node that the
pre-charge resistor is trying to charge up.  That inhibits the pre-charge
resistor operation and can cycle the DC-DC converter on and off
continuously, if your pre-charge resistor is always active.

Mike

> -----Original Message-----
> From: [hidden email] [mailto:[hidden email]] On
> Behalf Of Dennis Miles
> Sent: Sunday, October 07, 2012 12:25 PM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] pre-charge resistor?
>
> A lot of interesting discussion and use of Ohm's law in this series of
posts but
> the voltage of the pack varies in different paragraphs, in the first
couple of
> posts so I have been totally confused and I would ask, if you were my
> students, you to do the assignment "Explain implementing 'Pre-charging' ?"
> again to demonstrate competence.
> Any piece of EV equipment that is often disconnected and reconnected from
> the pack and has a large quantity of capacitive filtering in its input
circuitry
> benefits from "Pre-charging." The simplest and most reliable pre-charge
> implementation is a suitable relay engaged a few seconds before the main
> power contacter is engaged. The pre-charge relay supplies power from the
> pack only to the controller, feeding thru a current limiter to reduce
initial
> capacitor charge -up, the current limiter can be a "Power resistor" of 150
to
> 750 ohms, a wattage of 25 watts or more is used because their size makes
> them more immune to vibration cracking. An alternative is one or two light
> bulbs at 40 to 60 watts and rated for vibration service like used with
lights in
> ceiling fans in the home. Use one bulb for each
> 100 to 150 volts of pack voltage, in series! Note that one should not
switch
> other loads like the DC/DC on and off with the Controller and the
capacitive
> filtering in the input circuit of the DC/DC is much smaller in capacitance
and

> often includes an inductor so a pre-charge circuit is less necessary.
> Regards,
> *     Dennis *(EVprofessor.*sm*)* Miles*
>   *(863)944-9913* (phone noon to midnight E.S.T.)
> *    reply to [hidden email]*
> *        EVprofessor.sm is a Service Mark of:*
> *           Electric Vehicle Technical Institute inc.*
>
> On Mon, Oct 1, 2012 at 2:32 PM, Lee Hart <[hidden email]> wrote:
>
> > On 10/1/2012 9:12 AM, Danpatgal wrote:
> > > I have finally finished all the wiring on my new and improved
> > > Lectric
> > Leopard
> > > - now using lithium!
> >
> > Congratulations! I also have a Lectric Leopard. Its been reconverted,
> > so nothing of US Electricar's handiwork remains. But it's still on
> > lead (no dough for lithium).
> >
> > > pre-charge resistor... 750ohms... 68 volts across the main
contactor...

> > > After a few minutes I smelled the heated incandescent bulb kind of
> smell.
> >
> > Well, you have 68 volts across a 750 ohm resistor. Power = V^2 / R =
> > 68v^2 / 750ohms = 4624 / 750 = 6.165 watts. What wattage is your
> > precharge resistor? 6 watts is probably a good percentage of its
> > maximum wattage rating. It gets hot!
> >
> > > Then I read this thread (again), and the DIY thread here:
> > > http://www.diyelectriccar.com/forums/showthread.php?t=25419
> > > So, I have two questions:
> > >
> > > 1.- Is there any negative impact to having this low current path
> > > "on" all the time?
> >
> > Yes.
> >
> > 1. It slowly runs your pack dead. In your case, the precharge
> >     resistor current is I = V / R = 68v / 750ohms = 0.09 amps.
> >     This load alone will run your 130ah pack dead in about
> >     130ah / 0.09a = 1444 hours (about 2 months).
> >
> > 2. Your controller is precharged all the time. Even with the
> >     key off, if you step on the throttle, the motor will run
> >     momentarily on the charge in the controller's capacitors.
> >
> > > I assume that once the controller capacitors are charged and the
> > > DC-DC has charged the 12v battery (if necessary), it's pulling a
> > > very low level (a few watts ??) of power.
> >
> > It's pulling full pack voltage 120v x 0.09 amps = 10.8 watts all the
> > time. 6 watts is burned up by the precharge resistor, the rest is
> > powering the controller itself.
> >
> > > 2.- In the DIY thread, the author references a "Step-Start" device -
> > > is
> > that
> > > something available for purchase?
> >
> > I think he started that thread to sell his magic device. :-) However,
> > all you really need is a simple relay, with a 12vdc coil, and a
> > normally-open contact that can switch pack voltage at the current your
> > precharge resistor draws.
> >
> > Wire its 12v coil to turn on when you turn the key "on". Wire its
> > contacts in series with the precharge resistor. When the key is off,
> > the relay is off, and the precharge resistor is off. When you turn the
> > key on, wait a few seconds for the resistor to precharge the
> > controller then drive.
> >
> > The main contactor's coil is normally wired through the switch on the
> > potbox. Thus it won't pull in until you press the throttle, which will
> > (usually) be many seconds after you turned the key on. A typical
> > scenario is to get in the car, turn the key "on", put on your
> > seatbelt, adjust the mirror, shift into reverse, etc. *Then* press the
> throttle.
> >
> > A nice improvement is to wire a little neon indicator lamp from
> > controller B+ to B-. Mount it on the dash so you can see it, and label
> > it "Ready". When it's lit, the controller is precharged. This way, you
> > can turn on the key and wait for this indicator to light.
> >
> > A further improvement is to add a second relay, wired the same place
> > as the "Ready" indicator. This relay is rated for pack voltage, and
> > pulls in when the controller has precharged. When it pulls in, its
> > contacts enable the main contactor coil. This automatically provides
> > the precharge delay, so even if someone presses the throttle and
> > *then* turns on the key (which would provide no precharge), this
> > second relay keeps the main contactor off until the controller has
> precharged.
> >
> > Note 1:
> >
> > 0.09a is a pretty large precharge current. The Curtis controller
> > usually only draws 20ma, so I'll bet you also have your DC/DC
> > converter wired between controller B+ and B-. It's probably drawing
> > 0.07a out of that 0.09a total.
> >
> > The DC/DC should have its own precharge resistor across its power
> > switch (or relay, if you want it switched on/off with the key).
> >
> > Note 2: 750 ohms is a pretty large precharge resistance. It makes for
> > slow precharging, and doesn't reduce the voltage across the main
> > contactor all that much. Instead of 68v, you want to see something
> > under
> > 10 volts across the main contactor when it closes.
> >
> > I prefer to use ordinary 120v light bulbs as my precharge "resistor".
> > They are cheap, available, precharge quicker and more fully, and won't
> > overheat and fail if some fault condition keeps them in the circuit
> > longer than expected.
> >
> > > or ... is there a contactor that already has a precharge circuit
> > > built
> > in?
> > > It seems like this Gigavac unit does:
> > >    www.evsource.com/tls_gigavac.php
> >
> > No, it does not have built-in precharge. It *does* have built-in
> > economizer circuit for its *coil*, though. A coil economizer reduces
> > the current that the coil draws to hold it pulled in (saving 12vdc
power).
> > Here is my example:
> >
> > http://www.sunrise-ev.com/LeesEVs.htm (EV circuit #3)
> >
> > I don't know of a contactor with built-in precharge; but lots of
> > people make controllers and other devices with external precharge
circuits.

> > --
> > Anyone can make the simple complicated. Creativity is making the
> > complicated simple. -- Charles Mingus
> > --
> > Lee A. Hart http://www.sunrise-ev.com/LeesEVs [hidden email]
> >
> > _______________________________________________
> > | Moratorium on drag racing discussion is in effect.
> > | Please take those discussions elsewhere.  Thanks.
> > |
> > | REPLYING: address your message to [hidden email] only.
> > | Multiple-address or CCed messages may be rejected.
> > | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> > | OTHER HELP: http://evdl.org/help/
> > | CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
> >
>
>
>
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> | Please take those discussions elsewhere.  Thanks.
> |
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_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to [hidden email] only.
| Multiple-address or CCed messages may be rejected.
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Re: pre-charge resistor?

M. G.
In reply to this post by Mike Golub-2
Several electric forklifts have a PTC (positive temperature resistor) . It works just like a light bulb.

Sent from my Verizon Wireless Phone

----- Reply message -----
From: "Dennis Miles" <[hidden email]>
To: "Electric Vehicle Discussion List" <[hidden email]>
Subject: [EVDL] pre-charge resistor?
Date: Sun, Oct 7, 2012 2:24 pm


A lot of interesting discussion and use of Ohm's law in this series of
posts but the voltage of the pack varies in different paragraphs, in the
first couple of posts so I have been totally confused and I would ask, if
you were my students, you to do the assignment "Explain implementing
'Pre-charging' ?" again to demonstrate competence.
Any piece of EV equipment that is often disconnected and reconnected from
the pack and has a large quantity of capacitive filtering in its input
circuitry benefits from "Pre-charging." The simplest and most reliable
pre-charge implementation is a suitable relay engaged a few seconds before
the main power contacter is engaged. The pre-charge relay supplies power
from the pack only to the controller, feeding thru a current limiter to
reduce initial capacitor charge -up, the current limiter can be a "Power
resistor" of 150 to 750 ohms, a wattage of 25 watts or more is used because
their size makes them more immune to vibration cracking. An alternative is
one or two light bulbs at 40 to 60 watts and rated for vibration service
like used with lights in ceiling fans in the home. Use one bulb for each
100 to 150 volts of pack voltage, in series! Note that one should not
switch other loads like the DC/DC on and off with the Controller and the
capacitive filtering in the input circuit of the DC/DC is much smaller in
capacitance and often includes an inductor so a pre-charge circuit is less
necessary.
Regards,
*     Dennis *(EVprofessor.*sm*)* Miles*
  *(863)944-9913* (phone noon to midnight E.S.T.)
*    reply to [hidden email]*
*        EVprofessor.sm is a Service Mark of:*
*           Electric Vehicle Technical Institute inc.*

On Mon, Oct 1, 2012 at 2:32 PM, Lee Hart <[hidden email]> wrote:

> On 10/1/2012 9:12 AM, Danpatgal wrote:
> > I have finally finished all the wiring on my new and improved Lectric
> Leopard
> > - now using lithium!
>
> Congratulations! I also have a Lectric Leopard. Its been reconverted, so
> nothing of US Electricar's handiwork remains. But it's still on lead (no
> dough for lithium).
>
> > pre-charge resistor... 750ohms... 68 volts across the main contactor...
> > After a few minutes I smelled the heated incandescent bulb kind of smell.
>
> Well, you have 68 volts across a 750 ohm resistor. Power = V^2 / R =
> 68v^2 / 750ohms = 4624 / 750 = 6.165 watts. What wattage is your
> precharge resistor? 6 watts is probably a good percentage of its maximum
> wattage rating. It gets hot!
>
> > Then I read this thread (again), and the DIY thread here:
> > http://www.diyelectriccar.com/forums/showthread.php?t=25419
> > So, I have two questions:
> >
> > 1.- Is there any negative impact to having this low current path "on" all
> > the time?
>
> Yes.
>
> 1. It slowly runs your pack dead. In your case, the precharge
>     resistor current is I = V / R = 68v / 750ohms = 0.09 amps.
>     This load alone will run your 130ah pack dead in about
>     130ah / 0.09a = 1444 hours (about 2 months).
>
> 2. Your controller is precharged all the time. Even with the
>     key off, if you step on the throttle, the motor will run
>     momentarily on the charge in the controller's capacitors.
>
> > I assume that once the controller capacitors are charged and the
> > DC-DC has charged the 12v battery (if necessary), it's pulling a very low
> > level (a few watts ??) of power.
>
> It's pulling full pack voltage 120v x 0.09 amps = 10.8 watts all the
> time. 6 watts is burned up by the precharge resistor, the rest is
> powering the controller itself.
>
> > 2.- In the DIY thread, the author references a "Step-Start" device - is
> that
> > something available for purchase?
>
> I think he started that thread to sell his magic device. :-) However,
> all you really need is a simple relay, with a 12vdc coil, and a
> normally-open contact that can switch pack voltage at the current your
> precharge resistor draws.
>
> Wire its 12v coil to turn on when you turn the key "on". Wire its
> contacts in series with the precharge resistor. When the key is off, the
> relay is off, and the precharge resistor is off. When you turn the key
> on, wait a few seconds for the resistor to precharge the controller then
> drive.
>
> The main contactor's coil is normally wired through the switch on the
> potbox. Thus it won't pull in until you press the throttle, which will
> (usually) be many seconds after you turned the key on. A typical
> scenario is to get in the car, turn the key "on", put on your seatbelt,
> adjust the mirror, shift into reverse, etc. *Then* press the throttle.
>
> A nice improvement is to wire a little neon indicator lamp from
> controller B+ to B-. Mount it on the dash so you can see it, and label
> it "Ready". When it's lit, the controller is precharged. This way, you
> can turn on the key and wait for this indicator to light.
>
> A further improvement is to add a second relay, wired the same place as
> the "Ready" indicator. This relay is rated for pack voltage, and pulls
> in when the controller has precharged. When it pulls in, its contacts
> enable the main contactor coil. This automatically provides the
> precharge delay, so even if someone presses the throttle and *then*
> turns on the key (which would provide no precharge), this second relay
> keeps the main contactor off until the controller has precharged.
>
> Note 1:
>
> 0.09a is a pretty large precharge current. The Curtis controller usually
> only draws 20ma, so I'll bet you also have your DC/DC converter wired
> between controller B+ and B-. It's probably drawing 0.07a out of that
> 0.09a total.
>
> The DC/DC should have its own precharge resistor across its power switch
> (or relay, if you want it switched on/off with the key).
>
> Note 2: 750 ohms is a pretty large precharge resistance. It makes for
> slow precharging, and doesn't reduce the voltage across the main
> contactor all that much. Instead of 68v, you want to see something under
> 10 volts across the main contactor when it closes.
>
> I prefer to use ordinary 120v light bulbs as my precharge "resistor".
> They are cheap, available, precharge quicker and more fully, and won't
> overheat and fail if some fault condition keeps them in the circuit
> longer than expected.
>
> > or ... is there a contactor that already has a precharge circuit built
> in?
> > It seems like this Gigavac unit does:
> >    www.evsource.com/tls_gigavac.php
>
> No, it does not have built-in precharge. It *does* have built-in
> economizer circuit for its *coil*, though. A coil economizer reduces the
> current that the coil draws to hold it pulled in (saving 12vdc power).
> Here is my example:
>
> http://www.sunrise-ev.com/LeesEVs.htm (EV circuit #3)
>
> I don't know of a contactor with built-in precharge; but lots of people
> make controllers and other devices with external precharge circuits.
> --
> Anyone can make the simple complicated. Creativity is making the
> complicated simple. -- Charles Mingus
> --
> Lee A. Hart http://www.sunrise-ev.com/LeesEVs [hidden email]
>
> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
> | Please take those discussions elsewhere.  Thanks.
> |
> | REPLYING: address your message to [hidden email] only.
> | Multiple-address or CCed messages may be rejected.
> | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> | OTHER HELP: http://evdl.org/help/
> | CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
>



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|
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|
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Re: pre-charge resistor?

M. G.
In reply to this post by Mike Golub-2
More info ;
The ptc is connected across the main contactor. Any time the battery is connected it precharges the capacitors in the motor controller.

Sent from my Verizon Wireless Phone

----- Reply message -----
From: "[hidden email]" <[hidden email]>
To: "Electric Vehicle Discussion" <List <[hidden email]>, <>>
Subject: [EVDL] pre-charge resistor?
Date: Wed, Oct 10, 2012 7:15 am


Several electric forklifts have a PTC (positive temperature resistor) . It works just like a light bulb.

Sent from my Verizon Wireless Phone

----- Reply message -----
From: "Dennis Miles" <[hidden email]>
To: "Electric Vehicle Discussion List" <[hidden email]>
Subject: [EVDL] pre-charge resistor?
Date: Sun, Oct 7, 2012 2:24 pm


A lot of interesting discussion and use of Ohm's law in this series of
posts but the voltage of the pack varies in different paragraphs, in the
first couple of posts so I have been totally confused and I would ask, if
you were my students, you to do the assignment "Explain implementing
'Pre-charging' ?" again to demonstrate competence.
Any piece of EV equipment that is often disconnected and reconnected from
the pack and has a large quantity of capacitive filtering in its input
circuitry benefits from "Pre-charging." The simplest and most reliable
pre-charge implementation is a suitable relay engaged a few seconds before
the main power contacter is engaged. The pre-charge relay supplies power
from the pack only to the controller, feeding thru a current limiter to
reduce initial capacitor charge -up, the current limiter can be a "Power
resistor" of 150 to 750 ohms, a wattage of 25 watts or more is used because
their size makes them more immune to vibration cracking. An alternative is
one or two light bulbs at 40 to 60 watts and rated for vibration service
like used with lights in ceiling fans in the home. Use one bulb for each
100 to 150 volts of pack voltage, in series! Note that one should not
switch other loads like the DC/DC on and off with the Controller and the
capacitive filtering in the input circuit of the DC/DC is much smaller in
capacitance and often includes an inductor so a pre-charge circuit is less
necessary.
Regards,
*     Dennis *(EVprofessor.*sm*)* Miles*
  *(863)944-9913* (phone noon to midnight E.S.T.)
*    reply to [hidden email]*
*        EVprofessor.sm is a Service Mark of:*
*           Electric Vehicle Technical Institute inc.*

On Mon, Oct 1, 2012 at 2:32 PM, Lee Hart <[hidden email]> wrote:

> On 10/1/2012 9:12 AM, Danpatgal wrote:
> > I have finally finished all the wiring on my new and improved Lectric
> Leopard
> > - now using lithium!
>
> Congratulations! I also have a Lectric Leopard. Its been reconverted, so
> nothing of US Electricar's handiwork remains. But it's still on lead (no
> dough for lithium).
>
> > pre-charge resistor... 750ohms... 68 volts across the main contactor...
> > After a few minutes I smelled the heated incandescent bulb kind of smell.
>
> Well, you have 68 volts across a 750 ohm resistor. Power = V^2 / R =
> 68v^2 / 750ohms = 4624 / 750 = 6.165 watts. What wattage is your
> precharge resistor? 6 watts is probably a good percentage of its maximum
> wattage rating. It gets hot!
>
> > Then I read this thread (again), and the DIY thread here:
> > http://www.diyelectriccar.com/forums/showthread.php?t=25419
> > So, I have two questions:
> >
> > 1.- Is there any negative impact to having this low current path "on" all
> > the time?
>
> Yes.
>
> 1. It slowly runs your pack dead. In your case, the precharge
>     resistor current is I = V / R = 68v / 750ohms = 0.09 amps.
>     This load alone will run your 130ah pack dead in about
>     130ah / 0.09a = 1444 hours (about 2 months).
>
> 2. Your controller is precharged all the time. Even with the
>     key off, if you step on the throttle, the motor will run
>     momentarily on the charge in the controller's capacitors.
>
> > I assume that once the controller capacitors are charged and the
> > DC-DC has charged the 12v battery (if necessary), it's pulling a very low
> > level (a few watts ??) of power.
>
> It's pulling full pack voltage 120v x 0.09 amps = 10.8 watts all the
> time. 6 watts is burned up by the precharge resistor, the rest is
> powering the controller itself.
>
> > 2.- In the DIY thread, the author references a "Step-Start" device - is
> that
> > something available for purchase?
>
> I think he started that thread to sell his magic device. :-) However,
> all you really need is a simple relay, with a 12vdc coil, and a
> normally-open contact that can switch pack voltage at the current your
> precharge resistor draws.
>
> Wire its 12v coil to turn on when you turn the key "on". Wire its
> contacts in series with the precharge resistor. When the key is off, the
> relay is off, and the precharge resistor is off. When you turn the key
> on, wait a few seconds for the resistor to precharge the controller then
> drive.
>
> The main contactor's coil is normally wired through the switch on the
> potbox. Thus it won't pull in until you press the throttle, which will
> (usually) be many seconds after you turned the key on. A typical
> scenario is to get in the car, turn the key "on", put on your seatbelt,
> adjust the mirror, shift into reverse, etc. *Then* press the throttle.
>
> A nice improvement is to wire a little neon indicator lamp from
> controller B+ to B-. Mount it on the dash so you can see it, and label
> it "Ready". When it's lit, the controller is precharged. This way, you
> can turn on the key and wait for this indicator to light.
>
> A further improvement is to add a second relay, wired the same place as
> the "Ready" indicator. This relay is rated for pack voltage, and pulls
> in when the controller has precharged. When it pulls in, its contacts
> enable the main contactor coil. This automatically provides the
> precharge delay, so even if someone presses the throttle and *then*
> turns on the key (which would provide no precharge), this second relay
> keeps the main contactor off until the controller has precharged.
>
> Note 1:
>
> 0.09a is a pretty large precharge current. The Curtis controller usually
> only draws 20ma, so I'll bet you also have your DC/DC converter wired
> between controller B+ and B-. It's probably drawing 0.07a out of that
> 0.09a total.
>
> The DC/DC should have its own precharge resistor across its power switch
> (or relay, if you want it switched on/off with the key).
>
> Note 2: 750 ohms is a pretty large precharge resistance. It makes for
> slow precharging, and doesn't reduce the voltage across the main
> contactor all that much. Instead of 68v, you want to see something under
> 10 volts across the main contactor when it closes.
>
> I prefer to use ordinary 120v light bulbs as my precharge "resistor".
> They are cheap, available, precharge quicker and more fully, and won't
> overheat and fail if some fault condition keeps them in the circuit
> longer than expected.
>
> > or ... is there a contactor that already has a precharge circuit built
> in?
> > It seems like this Gigavac unit does:
> >    www.evsource.com/tls_gigavac.php
>
> No, it does not have built-in precharge. It *does* have built-in
> economizer circuit for its *coil*, though. A coil economizer reduces the
> current that the coil draws to hold it pulled in (saving 12vdc power).
> Here is my example:
>
> http://www.sunrise-ev.com/LeesEVs.htm (EV circuit #3)
>
> I don't know of a contactor with built-in precharge; but lots of people
> make controllers and other devices with external precharge circuits.
> --
> Anyone can make the simple complicated. Creativity is making the
> complicated simple. -- Charles Mingus
> --
> Lee A. Hart http://www.sunrise-ev.com/LeesEVs [hidden email]
>
> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
> | Please take those discussions elsewhere.  Thanks.
> |
> | REPLYING: address your message to [hidden email] only.
> | Multiple-address or CCed messages may be rejected.
> | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> | OTHER HELP: http://evdl.org/help/
> | CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
>



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|
| REPLYING: address your message to [hidden email] only.
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Re: pre-charge resistor?

EVDL Administrator
On 10 Oct 2012 at 23:05, [hidden email] wrote:

> Any time the battery is
> connected it precharges the capacitors in the motor controller.

If it's always connected, then what's the point of using a PTC?  Why not
just use a resistor, as Curtis recommends?

I'm leery of that too, actually.  I had a DCC-96 controller on my C-car many
years ago, when I was even more ignorant than I am today.  Rather than
precharge it, I just left the battery connected to it all the time! (I had a
manual breaker on the battery side as an emergency shutdown.)   I put the
main contactor on the motor side instead.  After a couple years of being
powered 24/7, the controller just up and quit one day.  

It might have been coincidence of course, but all gear has a MTBF.  If it's
powered up all the time, even through a resistor or PTC, won't that wind
down those life hours that much sooner?

David Roden - Akron, Ohio, USA
EVDL Administrator

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_______________________________________________
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| Please take those discussions elsewhere.  Thanks.
|
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Re: pre-charge resistor?

Roland Wiench
In reply to this post by M. G.
My EV uses two additional contactors which are call the safety contactors
that disconnects the battery negative and positive from the main contactor
and controller.

These safety contactors can also be turn off using several emergency turn
off switches through out the EV.

The safety contactors must come on first using the Ignition On circuit which
pre-charges the controller.  Turning on the Ignition Start, turns on the
main contactor.

This EV came with this start up sequence back in 75 and still using the same
circuits, contactors and relays today using a Zilla with no problems.

Roland


----- Original Message -----
From: "EVDL Administrator" <[hidden email]>
To: "Electric Vehicle Discussion List" <[hidden email]>
Sent: Thursday, October 11, 2012 10:18 AM
Subject: Re: [EVDL] pre-charge resistor?


> On 10 Oct 2012 at 23:05, [hidden email] wrote:
>
> > Any time the battery is
> > connected it precharges the capacitors in the motor controller.
>
> If it's always connected, then what's the point of using a PTC?  Why not
> just use a resistor, as Curtis recommends?
>
> I'm leery of that too, actually.  I had a DCC-96 controller on my C-car
> many
> years ago, when I was even more ignorant than I am today.  Rather than
> precharge it, I just left the battery connected to it all the time! (I had
> a
> manual breaker on the battery side as an emergency shutdown.)   I put the
> main contactor on the motor side instead.  After a couple years of being
> powered 24/7, the controller just up and quit one day.
>
> It might have been coincidence of course, but all gear has a MTBF.  If
> it's
> powered up all the time, even through a resistor or PTC, won't that wind
> down those life hours that much sooner?
>
> David Roden - Akron, Ohio, USA
> EVDL Administrator
>
> = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
> EVDL Information: http://www.evdl.org/help/
> = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
> Note: mail sent to "evpost" and "etpost" addresses will not
> reach me.  To send a private message, please obtain my
> email address from the webpage http://www.evdl.org/help/ .
> = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
>
>
> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
> | Please take those discussions elsewhere.  Thanks.
> |
> | REPLYING: address your message to [hidden email] only.
> | Multiple-address or CCed messages may be rejected.
> | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> | OTHER HELP: http://evdl.org/help/
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>

_______________________________________________
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|
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Re: pre-charge resistor?

Dennis Miles
In reply to this post by EVDL Administrator
< all gear has a MTBF.  If it's powered up all the time,>
< even through a resistor or PTC, won't that wind <
<down those life hours that much sooner?>

Not exactly, the "Mean Time Between Fails," is a (Sort of) average
compilation over many units, not a particular units guaranteed failure
time. With most electronics the first hour of operation will be death for
80% of items destined to fail the first year, and the first ten hours will
bring the death of another 80% of those who didn't fail the first hour but
will the first year, that leaves about 96% to continue to work, and those
parts which don't fail in the first year are likely to continue to work for
ten more years, if you don't drop a screwdriver or wrench into the circuit
with power applied and "Murder" a component.
Regards,
*     Dennis *(EVprofessor)* Miles*
  *(863)944-9913* (phone noon to midnight E.S.T.)
*    reply to [hidden email]*
*++++++++++++++++++++++++++++++++++++++
*
On Thu, Oct 11, 2012 at 12:18 PM, EVDL Administrator <[hidden email]>wrote:

> On 10 Oct 2012 at 23:05, [hidden email] wrote:
>
> > Any time the battery is
> > connected it precharges the capacitors in the motor controller.
>
> If it's always connected, then what's the point of using a PTC?  Why not
> just use a resistor, as Curtis recommends?
>
> I'm leery of that too, actually.  I had a DCC-96 controller on my C-car
> many
> years ago, when I was even more ignorant than I am today.  Rather than
> precharge it, I just left the battery connected to it all the time! (I had
> a
> manual breaker on the battery side as an emergency shutdown.)   I put the
> main contactor on the motor side instead.  After a couple years of being
> powered 24/7, the controller just up and quit one day.
>
> It might have been coincidence of course, but all gear has a MTBF.  If it's
> powered up all the time, even through a resistor or PTC, won't that wind
> down those life hours that much sooner?
>
> David Roden - Akron, Ohio, USA
> EVDL Administrator
>
> = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
> EVDL Information: http://www.evdl.org/help/
> = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
> Note: mail sent to "evpost" and "etpost" addresses will not
> reach me.  To send a private message, please obtain my
> email address from the webpage http://www.evdl.org/help/ .
> = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
>
>
> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
> | Please take those discussions elsewhere.  Thanks.
> |
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Re: pre-charge resistor?

Lee Hart
On 10/18/2012 11:25 PM, Dennis Miles wrote:
> the "Mean Time Between Fails," is a (Sort of) average compilation
> over many units, not a particular units guaranteed failure time...

That's a good summary. Of course, the exact numbers vary significantly
depending on the product.

Here's a way to describe it that's easy to remember. Think of the cross
section of a bathtub (view with a fixed-width font like Courier). It
starts high at the faucet/drain end, but falls very quickly to the
bottom. It then has a long, nearly flat bottom. Then at the far end, it
rises back to the top, somewhat slower than it did at the faucet/drain end.

  |                    _-
  |                  _-
   \________________-

This is the "bathtub curve" as it is known to reliability engineers. The
horizontal axis is time (in hours or even years). The height is the
failure rate. High means very likely to fail; low means very unlikely to
fail.

Something brand new (time=0, at the left end) has a very high failure
rate. Maybe 10% of them don't work right out of the box! Hopefully, the
company you bought it from tested it, and weeded out all these "infant
mortality" failures so you won't see them. (Of course, this step is left
out if you buy something cheap with no warranty or return options).

If it works for the first few weeks, you get into the low flat bottom of
the bathtub. Any weak parts, careless assembly, or other problems have
been weeded out. The product is likely to work for a long time.

As it gets old, the failure rate gradually starts to rise. This is the
"wear out" portion of the curve. Just about *everything* has a wear-out
mechanism. It could be months or years, depending on the type of
product, how often you use it, how hot it gets, how hard you are
stressing it, etc.

And, it depends on luck. :-) You could buy two identical products, and
use them in identical applications. But one lasts a month, and one lasts
10 years. It's just the luck of the draw.

You won't see the shape of this curve until you are buying 100's of
something. If you carefully record exactly when each one fails, then you
will see the shape of this curve. Most of the failures will either be
from infant mortality, or wearout, with just a few random failures in
between.

--
Humanity is acquiring all the right technology for all the wrong
reasons. -- R. Buckminster Fuller
--
Lee A. Hart http://www.sunrise-ev.com/LeesEVs [hidden email]

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