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Discussion Starter · #1 ·
I've got the complete battery pack out of a 2014 Chevy Spark EV (battery made by A123). I can control the contactors in the pack to enable the connection to the charger and separately the main connection to everything else.

What I need to do is be able to confirm that the pre-charge circuit (to the charger) is operating as expected. My multimeter can read up to 1000v (pack is 370v), but when I enable the pre-charger circuit the meter takes ~1sec to update. It could be signalling over-voltage or it could be just taking its time to go from 0 to 370v.

Is there a way to confirm that the pre-charger circuit is functioning, i.e. limiting in-rush, other than seeing if it kills my charger?

Thanks
Jeff
 

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I've got the complete battery pack out of a 2014 Chevy Spark EV (battery made by A123). I can control the contactors in the pack to enable the connection to the charger and separately the main connection to everything else.

What I need to do is be able to confirm that the pre-charge circuit (to the charger) is operating as expected. My multimeter can read up to 1000v (pack is 370v), but when I enable the pre-charger circuit the meter takes ~1sec to update. It could be signalling over-voltage or it could be just taking its time to go from 0 to 370v.

Is there a way to confirm that the pre-charger circuit is functioning, i.e. limiting in-rush, other than seeing if it kills my charger?

Thanks
Jeff
Not sure but this might work: Load pre-charge circuit output leads with three series connected 110V incandescent light bulbs. If working correctly, the bulbs should start dimer and then go brighter after pre-charge time. This assumes pre-charger is a simple timer implementation and not one based on a feedback charge voltage measurement.

Don't leave on more than a minute to prevent over heating of pre-charge resistor incase its not working properly.
 

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Hi Jeff
I would suspect that your pre-charge is NOT working
I started using a Chevy Volt system but when I just connected the pre-charge resistor without the mark space ratio system I just killed the resister

I'm now using an old kettle element and it takes several seconds (5 or 6) before the voltage gets up there and I switch the main contactor on
 

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Discussion Starter · #4 ·
Hi Jeff
I would suspect that your pre-charge is NOT working
I started using a Chevy Volt system but when I just connected the pre-charge resistor without the mark space ratio system I just killed the resister

I'm now using an old kettle element and it takes several seconds (5 or 6) before the voltage gets up there and I switch the main contactor on
Your mention of 'mark space ratio' is interesting... The Spark EV maintenance manual describes the pre-charger control line as PWM. So you're​ saying that hitting the resistor with 100% all-on would kill the resistor. I can test the resistor to see if it's dead or working, and go from there.

Not sure I understand the purpose of PWM input to a pre-charger circuit? If PWM can 'protect' the resistor...?

Thanks
Jeff

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Discussion Starter · #5 ·
Not sure but this might work: Load pre-charge circuit output leads with three series connected 110V incandescent light bulbs. If working correctly, the bulbs should start dimer and then go brighter after pre-charge time. This assumes pre-charger is a simple timer implementation and not one based on a feedback charge voltage measurement.

Don't leave on more than a minute to prevent over heating of pre-charge resistor incase its not working properly.
This came to mind but I was uncertain how long the bulb brighter period would last, i.e. how fast does the pre-charge actually take. If it were small fractions of a second it might not be perceivable.

The control circuit for the A123 pack seems pretty sophisticated, including some custom A123 parts for current monitoring and protection (I posted some details on another thread of mine about the A123 pack). This makes me more confident than not that they use a voltage equivalence method to disengage the pre-charger rather than a timer, but I'm guessing, so not 100% sure.

Jeff

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Hi Jeff
I looked at the Chevy resister and thought - looks big enough - so I just used it for the controller pre-charge
It died!
The Chevy contactors didn't like me either - so I spent some money on some bigger ones

I'm currently using one of the Chevy contactors as my pre-charge contactor - and a bigger contactor as my main
 

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Discussion Starter · #7 ·
Hi Jeff
I looked at the Chevy resister and thought - looks big enough - so I just used it for the controller pre-charge
It died!...
I tested the resistor tonight in the pre-charge circuit and it is spot on 25 Ohms. It is a RARA IRV80 25 Ohms +-5% tolerance 2500V DH 32.

Next up is to test a PWM signal to the pre-charge circuit control. I'm going to use a solid state relay to isolate the arduino from the signal to the pack.

Not sure what frequency to run the PWM at. I'm guessing start at 100hz (something a cheap automotive controller could handle) with a low duty cycle, just to see where the circuit begins to provide power into the charger line.

Jeff
 
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