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Old 08-04-2009, 03:00 AM   #2140 (permalink)
MPaulHolmes's Avatar
Join Date: Feb 2008
Location: Maricopa, AZ (sort of. Actually outside of town)
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Michael's Electric Beetle - '71 Volkswagen Superbeetle 500000
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Man, when you said you wanted to be a beta tester, you weren't joking! I wonder what caused the latching. I'm going to make the next one with a LEM 500. I don't know if that has anything to do with anything, but there must be a reason they call a LEM 300 a LEM 300 (300 amps hehe, as opposed to 500 amps).

The EVTech people told me that too fast of a change in voltage or too large a voltage into an A/D channel can cause latchup.

Joe, one experiment you could do, (although I don't recommend it) is to turn up the hardware overcurrent shutdown point some (also change the software to allow for higher current) then slam on the gas. I predict at 16 MHz that you would get latchup with the LEM 300. It's actually a very noisy signal. I looked at it on the oscilloscope. It seems to me to be the most obvious cause of the latchup.

Anyway! Temperature is what we're talking about! Sounds like good savings for the mosfets. Cutting the resistance from 20 Ohms to 10 Ohms could only be done safely if we used 2 mosfet drivers. Voltage spikes would increase. Any idea what they are like right now? 144v isn't too close to 200v, but it isn't really far away either.

One thing to consider: The capacitors are rated for 3000 hours at 105 degC. Right now they are only getting into the 60's so that doesn't sound that bad. Even if they did get to 100 degC, if you drove for 1 hour per day at 100 degC, you could drive for around 10 years.
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