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Old 09-12-2010, 10:39 PM   #3762 (permalink)
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Originally Posted by MPaulHolmes View Post
I'm using 200v mosfets, and at 500 amps, the voltage spikes are around 13v. So, for a 144v battery pack, the spikes go up to around 157v or so. That's with a power section that consists of a capacitor bank from B+ to B-, freewheel diodes from B+ to M-, and mosfets from M- to B-.
Very interesting. Based on my testing with a small inductive load, I would have expected a lot higher voltage spikes. Maybe the low resistance of the motor is dampening the spikes? Would you be able to post the O-scope waveforms? Also, what type of motor are you using? I assume it is under a load if you're pulling 500 amps? Is there any way you can measure the peak current through your diodes? (Maybe putting a fractional ohm resistor in series and measuring the voltage drop of the resistor?) I'm trying to decide between mosfets and IGBT's for my controller. If I can safely keep a comfortable margin between voltage spikes and max source-drain voltage, I may go with mosfets. If there's any question of a safety margin, I'll go with IGBT's.

P.S. -- It's great to have someone with an actual motor for testing. Thanks for your help.

Last edited by princeton; 09-12-2010 at 11:08 PM..
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