# Pre Charging an Open Revolt



## Ace_bridger (Nov 22, 2011)

...and can I pre charge from 12V or would it need to be pack voltage?

Cheers,

Adam


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## Tesseract (Sep 27, 2008)

Ace_bridger said:


> 1) Do I need to pre charge?
> 2) Why do I need to pre charge?
> 3) How do I pre charge? Can I just have a switch and appropriate resistor and wait a few seconds until I know they're charged or do I need something more...complex?
> ...and can I pre charge from 12V or would it need to be pack voltage?


1) Yes.
2) Because when you turn on the controller the input capacitors look essentially like a short circuit - the peak current to charge the caps will be approximately equal to Pack Voltage / (Battery Pack Resistance + Capacitor Internal Resistance). That will almost certainly be in the 10kA range. This kind of surge current can do all sorts of damage as you might imagine.
3) The controller should handle precharge, not you. That said, the usual way of precharging the input capacitors is to use a relay to bridge the main contactor with a wirewound resistor. The main contactor is closed either when dV/dt drops below a certain rate or after a certain amount of time. I prefer the former method; many people go with the latter method as it is simpler to implement.
4) No, you must bring the capacitor up to within a few volts, at most, of the pack.


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## Ace_bridger (Nov 22, 2011)

Thanks Tesser. That's cleared that up then. I think the Open Revolt doesn't handle pre charge as in the instructions it says that the caps will need pre charging.

Adding a suitable resistor switched seperately to the controller sounds simplest to me.

Many thanks,

Adam


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## jackbauer (Jan 12, 2008)

The revolt does have a contactor driver and timer function. What you need to do is to switch in a resistor (i use 100R 10W) across the main contactor with a relay when the key is turned on. Then the controller will wait until the precharge timer has expired before closing the main contactor. You will need the rtd explorer software on a laptop connected to the controller serial port to program the pre charge function.


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## Ace_bridger (Nov 22, 2011)

Jack,

You're a legend, that's exactly what I needed to know, many thanks.

Adam


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## electricmini (Oct 21, 2008)

Hi Adam

Just a quick thought, use a suitable HV-rated relay to connect the
precharge resistor across your contactor, so that when the car is
switched off, the contactor AND the precharge relay are off.

If you just wire the resistor permanently across your main contactor
(as some people do with Curtis controllers) then the controller's
capacitors are always energised. There is enough energy in them to give
a pretty nasty shock, perhaps even move the vehicle if it is in gear.

It's much better for safety's sake to have TWO main contactors,
one in the negative pack cable (switched on with a kill switch or suchlike)
and one in the positive pack cable, so when the car is off the pack is
totally isolated from the controller. The negative contactor could also be
one of those Albright "Big Red Buttons", if preferred.

This also helps avoid leakage currents due to brush dust in the motor from
giving you nuisance RCD trips if you use a non-isolated charger

Regards

Richard (electricmini)


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## Ace_bridger (Nov 22, 2011)

Richard,

I think those suggestions, combined with the Open Revolt functionality, sound like a pretty sensible approach.

Just need to find a HV relay!!

Cheers,

Adam


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## mora (Nov 11, 2009)

Ebay for kilovac EV200 contactor. Should be "cheap" and handles high voltages. I use two with my OpenRevolt setup. One acts as main contactor and the other is for precharge only. OpenRevolt controls 12V relay which controls both contactors. When I turn the key precharge contactor closes. OpenRevolt begins counting and operates relay after counting finishes. Main contactor closes and precharge contactor opens at the same time. Both contactors open when I turn ignition power off.


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## Ace_bridger (Nov 22, 2011)

Thanks Mora. The EV200 definitely looks like the one worth going with. I see they sell them as pairs too...saves a few pence!!

I was going to use two. One on the +ve operated by the 'ignition' switch and one on the negative operated by a 'big red button' which will be located within reach of driver and passenger.

Am i correct in thinking that you use an EV200 as a relay to switch in your pre-charge resistor? Did I read that correctly or have I misunderstood you?

I love this forum, it's full of people who like doing stuff well without unnecessary spending 

I calculated that my EV should pay for itself, from fuel saving and tax saving, within 2.5 years!!


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## mora (Nov 11, 2009)

Yes, that's right. I use general purpose (or automotive) 12V relay which controls two contactors. I've added a picture to this post about this control thing. Upper half of image represents high voltage side, lower half low voltage (12V) side.


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## Ace_bridger (Nov 22, 2011)

Many thanks Mora. That's very kind of you. All makes sense.


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## Duncan (Dec 8, 2008)

Hi Guys

Why do you need a contactor for the precharge?

I was simply planning on using a switch

- the current is limited by the resister and you can open the switch after the main contactor pulls in when there is no voltage across the switch


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## DJBecker (Nov 3, 2010)

Duncan said:


> Hi Guys
> 
> Why do you need a contactor for the precharge?
> 
> ...


The precharge circuit should carry only modest current, so you can use a low cost relay rather than an expensive contactor. The relay is typically mounted adjacent to the final contactor to simplify the wiring.

Using only a switch would bring traction voltage into the passenger compartment.

You don't need multiple contactors just because you have multiple emergency stop methods. The main contactor often has the control voltage routed through multiple switches and lock-out relays. Anything that goes wrong will break the circuit and open the contactor. If you have multiple contactors, for instance to completely isolate a remote battery pack, the "big red button" manual shutdown should open all of them.


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## ACEVS4US (Jul 21, 2011)

I,m working on my precharge circuit myself at the moment.

You can't/shouldn't use standard relays for precharge as far as I can tell. Standard power relays are not useful for more than about 30V dc, when there is current draw at "make/break time". They have ac voltage ratings of typically 240VAC but this doesn't apply for DC as well. The problem with standard relays and DC (above 30V) is that the arc at "make/break time" persists for too long and can cause fusing of the contacts (even at currents of 5A or so). For this reason I think it is better to use a contactor.


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## Duncan (Dec 8, 2008)

ACEVS4US said:


> I,m working on my precharge circuit myself at the moment.
> 
> You can't/shouldn't use standard relays for precharge as far as I can tell. Standard power relays are not useful for more than about 30V dc, when there is current draw at "make/break time". They have ac voltage ratings of typically 240VAC but this doesn't apply for DC as well. The problem with standard relays and DC (above 30V) is that the arc at "make/break time" persists for too long and can cause fusing of the contacts (even at currents of 5A or so). For this reason I think it is better to use a contactor.



Why would you have 5 amps going through a pre-charge circuit?
The whole idea is to use a resister to reduce the current at switch ON - and there should be no current at all at switch OFF

I am going to use either a small automotive relay or even a switch


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## Ziggythewiz (May 16, 2010)

I use a $4 switch for mine. You're not bringing pack voltage into the cabin anymore than having a voltmeter there does. Switch on the inside, wires behind the firewall. Resistor is large enough it can't do much anyway, not that I would lick it, but anything less and you couldn't feel it.


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## Camaro (Jul 29, 2008)

Ziggythewiz said:


> I use a $4 switch for mine. You're not bringing pack voltage into the cabin anymore than having a voltmeter there does. Switch on the inside, wires behind the firewall. Resistor is large enough it can't do much anyway, not that I would lick it, but anything less and you couldn't feel it.


How much voltage is your pack going to be? Mine is 144v and I bet I could feel that if I some how shorted a switch with my finger.
I have a completely isolated voltage monitoring circuit that uses an xbee to communicate with my main mother board and hand held controller. The mother board tells my modified Open Revolt controller to close the contactor when the caps are above 140 volts. It also tells my displays in the cabin what the pack voltage is. Nothing higher than 12v in the cabin. 
As a benifit, the hand held touch screen display that I use to lock/unlock my doors, crack the windows, start the cabin heat, ect... can also read the pack voltage while I'm in at work or at home in the house.

Yes you can use a switch, but... there are so many cool ways to do things now a days.


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