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Old 07-14-2012, 12:00 PM
Ace_bridger Ace_bridger is online now
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Default Pre-Charger Indication

I've recently built an Open Revolt controller for my Golf and will be connecting in the next couple of weeks.

I'll be switching the pre-charge contactor off the ignition and using the Open Revolt contactor driver to switch in the main contactor after 10 seconds.

I have a concern that I will not know whether the controller is actually pre-charging or not. I fear that if something was not working correctly in the pre-charge circuit I would have no idea until 10 secs after I've switched on the ignition when the controller explodes!!

I have a couple of thoughts,

1) have a simple potential divider circuit, to step the 144V down to 12V, connected to battery +ve and -ve (at the controller) which would switch a relay to controller a lamp in the cab. That way I would know that there was 144V at the contoller when I switch on the ignition.

2) Keep it simple and just have a volt meter, mounted in the cab, monitoring voltage across the B+ve and B-ve (at the controller). This would also allow me to monitor pack voltage at any time the car is running.

Is option 2 a valid solution or do I need to worry about creating a more sophisticated solution?

Ideas and suggestions very welcome.

Cheers,

Adam
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1993 VW Golf Mk2, 9'' ADC, Open Revolt, Trojan 150Ah 12x12V batteries, 2.5KW Elcon charger, motorsport hall effect throttle.

Last edited by Ace_bridger; 07-14-2012 at 12:50 PM.
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  #2  
Old 07-14-2012, 03:02 PM
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Ziggythewiz Ziggythewiz is offline
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Default Re: Pre-Charger Indication

KISS

You should have a voltmeter anyway
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Old 07-14-2012, 03:50 PM
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Default Re: Pre-Charger Indication

I use voltmeter too. I've wired green and red leds to dashboard to indicate which contactor receives +12V. But that doesn't guarantee that precharge goes on. Few times I've had contactor receive +12V but it doesn't close the circuit. Of course it was the precharge contactor that failed to operate. I can spot this kind of failure easily by reading voltmeter whenever I turn the key. No rising voltage = turn off and try again.

Don't worry, controller won't explode first. You'll likely weld your contactor to closed state after few clicks of no precharge. Ask me how I know, hehehe. My controller has been abused when it comes to capacitors. And still EV200 contactor failed first.

This precharge thing should be better in OpenRevolt. It is automated in 1000A version but it isn't finished yet.
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Old 07-15-2012, 01:03 AM
Ace_bridger Ace_bridger is online now
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Default Re: Pre-Charger Indication

Thanks for responses. I have a suitable voltmeter and will mount it in the cab with the ammeter.
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Old 07-15-2012, 06:12 AM
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Default Re: Pre-Charger Indication

Quote:
Originally Posted by mora View Post
This precharge thing should be better in OpenRevolt. It is automated in 1000A version but it isn't finished yet.
Is it automated with a timer or sensors? I like the manual approach (I flick a $5 switch, wait 6-8 sec, and turn the key when I think the charge is high enough; with my controller it only gets to 70%) because if anything fails I don't turn the key. If the controller were to ever start full on, it would eat the precharge without moving the car.

If I were to do an automated circuit, I would want it sensor based with multiple switches to ensure the voltage is getting up and get it there quicker. I've seen a number of complicated precharge circuits, but they still wait 10+ seconds. Why not switch in lower value reistors as the precharge progresses to keep the current up and get there faster?
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Old 07-15-2012, 12:31 PM
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Default Re: Pre-Charger Indication

I remember it being some kind of comparison between voltage and time. First voltage rises fast and when caps are full enough rise time gets slower. When voltage rise is slow enough in some pre-set time window then controller would close the main contactor. Low value resistors must have been used as actual precharge times were pretty short when being tested. MPaulHolmes will likely give better description of this precharge circuit.
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Old 07-15-2012, 12:57 PM
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Default Re: Pre-Charger Indication

I guess waiting for dV/dT to slow to a pre-determined rate would be sensible.

To keep the thread on track...I'll use a voltmeter to ensure that I have 144V (ish) at the controller when I turn on the ignition.
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Old 07-15-2012, 02:11 PM
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Default Re: Pre-Charger Indication

Sounds good. I don't know about the ReVolt, but on my curtis with the specified resistor I only get up to about 90V of 120 nom
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Old 07-15-2012, 11:44 PM
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Lightbulb Re: Pre-Charger Indication

There are some sophisticated ways to deal with precharging and I'm working on some with my DC-DC boost converter. But a very simple approach would be to use an inexpensive ($5) 24 VDC relay like this:

According to the specs, it has 650 ohms resistance and a pull-in voltage of about 80%, or about 19.2 volts (30mA). So you could add a series resistor of (120-19)/0.03 = 3.4k (5W) so the relay will pull in when the charge voltage is close enough, and wire the contacts in series with the ignition switch so it won't energize the main contactor until the voltage is at a safe level. It only wastes about 3 watts, but you could disconnect it with an auxiliary contact or other means.

It can also be accomplished with a solid state relay which draws much less current. And a 120 VAC relay coil will also work on DC with less current, but you need to add the right resistance. 120 VDC coils exist but are rare.

Those are the simple methods. I'm planning on using a MOSFET with a zener and two resistors, for a cost of a couple dollars and only a couple milliamps draw. And depending on the amount of current involved you might be able to drive a MOSFET with PWM at a constant current until the capacitors are charged. That would be the fastest way to a full charge, and would be an interesting microcontroller project.

Last edited by PStechPaul; 07-15-2012 at 11:48 PM.
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Old 07-16-2012, 04:56 PM
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Default Re: Pre-Charger Indication

Hi Guy's
I am about to buy a suitable resistor for pre-charge, what value of resistor do you guy's use for use on 150v?
John
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