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Old 08-19-2013, 09:50 PM   #1 (permalink)
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Unhappy MOSFET fireworks

Hello,

I am having trouble with the Paul and Sabrina open Revolt controller.
Currently I am on my 3rd set of MOSFETs . for some reason, one MOSFET will blow then (if allowed to) the rest will. as far as I can tell everything is assembled correctly, nothing is getting terribly hot, I practiced proper static precautions during assembly and I have a pre-charge resistor.
please help!!! I'm going broke buying new FETs, not to mention insane with frustration.

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Old 08-20-2013, 04:52 PM   #2 (permalink)
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Under what conditions did the first mosfet fail? You may need a new mosfet driver too. There are a lot of variables. Did it ever work under a heavy load?
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Old 08-20-2013, 05:05 PM   #3 (permalink)
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I tested the controller under various loads. I will normally draw 100A during constant speed and during acceleration 200-300A. I peaked at 400A for a couple seconds to see how it would handle, no problems. then the next day, I took it for a test drive. taking it easy on the throttle, trying to stay below ~250A. I heard and smelled a FET explode around 200A.

these are all Battery current measurements, I don't know what the motor current was.... luckily the other FET's are still switching, the driver is still working, and the Zener hasn't shorted. in previous explosions, the Zener would short....

I have a second power PCB, so I'm currently thinking of hooking up two in parallel to current share the load.

this is not a very large vehicle: 81' Bradley GTE, 142V 100Ah LiFEPO4 (CALB)
8" 20.9HP GE brushed motor
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Old 08-21-2013, 07:43 PM   #4 (permalink)
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Where did you buy those transistors? I heard a few stories about counterfeit ones - cheaper low rating elements with new symbols engraved
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Old 08-22-2013, 08:24 AM   #5 (permalink)
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the most recent batch I got from Mouser, the last two batches I got from Digikey.
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Old 08-23-2013, 09:12 AM   #6 (permalink)
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Battery amps could be half the motor amps. The motor amps is what the MOSFET's handle.

Alvin
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Old 08-23-2013, 03:20 PM   #7 (permalink)
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yes, I was concerned about motor current. I can only mention what the battery current was because that is where my sensors are. next test drive I will hook up a motor voltage gauge....

the BMS will not allow a discharge greater than 400A (batt current).

could the motor current be greater than double the battery current? 3X? 4X? I'm just wondering where to set the current limit on the Revolt....and if there is something obvious that I've missed. well, obvious to someone else at least.
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Old 08-23-2013, 03:21 PM   #8 (permalink)
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has anyone hooked up two of the power boards in parallel for a super Revolt? I have two sets of parts because of my MOSFET fireworks, so I could...
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Old 08-23-2013, 04:41 PM   #9 (permalink)
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VR1 on the control board is how you adjust the amp limit. I am not sure which way lowers it I think counterclockwise. Mine has always been at the lowest limit and I have never hit that.

You would think that there is enough headroom on those MOSFET's .

It must be something else. When I soldered mine on I heated the gun till it was red then soldered for only a second or two.

Mine has been in service for 4 years now without any trouble other than the cheap potetiometers that I use.

Alvin
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Old 08-23-2013, 05:06 PM   #10 (permalink)
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VR1 was set to ~half. after the most recent MOSFET fried, I turned it CCW, but haven't tried it since.... maybe I will when I get home from work tonight!!
ya, it does take a lot of heat to get the solder to wick in. I used a heat gun and a high power soldering iron.

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