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Old 11-29-2009, 11:21 AM   #2656 (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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Hey Greg! I'm going to start ordering the AtMega168 instead. The Atmega8 is pin compatible with it, so there are no software or hardware changes necessary. The poor ATMega8 was just about full! hehe. Now we will have 16k flash memory instead of 8k.

Ya, all the little bolts and screws and who knows what comes with it. The only thing that I haven't included in the past is some sort of glue when you stick the little thermistor into the hole drilled in the face of the heat spreader, but I'm pretty sure metric based glue will work well there.

Battery amps are being measured in software. Just a couple lines would be needed to disable the mosfets for a particular number of pwm periods if the battery amps exceeded 300.

This controller has a ripple rating of about 180 amps. Fran was telling me that worst case ripple current is at 50% duty, which is half of the motor amps, or 250amp in this case. So, it's almost rated continuous for the worst case. You could put in some 1000uF caps instead of the 820uF ones I've been using. They would barely fit, and you would then have a ripple rating of about 190amp, with a 20% reduction in ESR.

Joe in Phoenix wasn't having trouble with them overheating in 40-45 degC weather with his driving. Not a lot of mountains though. The temp of the capacitors climbed to around 65 degC, and held there. They are rated for 3000 hours at 105 degC. I hear you double the life for every 10degC drop in temp, so they should be good for around 12,000 hours?

One thing to note: Even at 0 rpm with a locked rotor, the motor current still follows the throttle really well. I've graphed the results of it. No overshoot from a step response. So no concern about large current near 0 rpm, unless you feel like making large current near 0 rpm. In which case you just step on the pedal more! hehe.

I've made a prototype 144v 700amp controller with some Schottky 200v 120amp freewheel diodes. They seem very well matched to the 200v 130amp mosfets. I haven't tested it at 700amps though. I mailed it off to someone. I couldn't have safely tested it with my crappy motor I think. The schottky version costs an extra $50 for the price of the very expensive stinking diodes! Over $8 each! ripoff! We were going to add that as an option on the kit page I think. It just concerns me that I haven't tested it at that current level. It's definitely in the prototype phase. At least I can say for sure that the 60 amp diodes work for quite a while. Ian from Zeva has used them in a controller for about 1 year now, and nothing has exploded! Joe's controller has run since the beginning of July.

By the way:

One annoying thing about the controller is that you need to turn on the 12v power to the controller before closing the main contactor and pre-charge circuit. Well, that's just to be safe. In reality, I think it's not a problem to precharge at the same time, but I would turn the 12v power on first, and off last. It has all the logic protecting against overcurrent and undervoltage. Also, the 12v power input needs to be isolated from the pack voltage. So, use the car's 12v auxiliary battery, or a DC-DC supply or something. The input can be anything in the range of 9v to 18v.
kits and boards

Last edited by MPaulHolmes; 11-29-2009 at 11:27 AM..
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