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Old 04-28-2009, 08:02 AM   #1063 (permalink)
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Join Date: Apr 2009
Location: Colorado Springs
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Is there a summary page for your project? I skimmed the first 100+ posts and the last dozen or so, but a thousand posts! I dunno if I have time to read them all. I hate to say something that is already old news but based on what I've read:

This is very cool what you are doing but your electronics is not very impressive. I'm not surprised if you are burning up FETs etc. I'd like to know where you have gone from the original uC to single sided FET drive and DC motor circuit? If you are still doing that, here are my comments:
1. I’m not sure if your FETS have “body diodes” but if they don’t you should add external diodes across the FETs. This may also allow for some braking energy recovery, but ideally that would take a fully “synchronous buck regulator” type circuit. And it depends on the motor details too, ie is it a PM field or a coil. I don’t think many large motors use PM fields, yes/no? If the motor has a field coil, a separate field controller circuit would be the way to go.
2. A micro controller is an interesting way to make PWM pulses. The uC can do things a simple comparator cannot, but it will be very frequency limited and potentially hang up etc. Using a POT for a throttle is another dubious choice. I would probably just use switches like a cruise control, including the brake switch.
3. High voltage (600 to 1KV) FETs from STMicro etc are surprisingly inexpensive. I don't think IR makes anything in that range??? In any case, I think most commercial controllers use IGBTs below say 20KHz. If your PWM is above 50KHz then yes, you need FETs.
4. DC motors make the controller real simple but brushes etc are a maintenance issue. I expect most commercial EVs are actually multi phase motors similar to a 3-phase AC motor. Again, this would require a more sophisticated controller.
5. You talked a lot about pre-charge resistors but I don’t see them on the schematic? I would expect such a thing between the batteries and the capacitors, with a switch to bypass them once the system is up? You’re not talking about the FET gate network resistors, are you?

I’m already speculating and projecting too much. Please show us where you are now so I don’t look stupid making bad assumptions.

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