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Old 07-06-2011, 05:20 PM   #4911 (permalink)
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Have you tried an RC snubber? I'm trying that on a new driver board.

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Old 07-06-2011, 09:57 PM   #4912 (permalink)
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Quote:
Originally Posted by jackbauer View Post
Looks like the VLA is driving my gate off too fast. Common problem at my age i'm told
You put all of that effort into a fast, high current gate drive only to find that you need to slow it down.

What you want is a gate drive that operates at full gate current until the controlled voltage starts to rise, then drops to a low power mode. That way the device goes through the high power dissipation regime at maximum switching speed, but slows down at the end. Ideally you want to be just slightly under-damped (not critically damped) with a slight voltage bump.

I've seen discrete circuits that do this by shutting off the gate drive when the voltage starts to rise, using the propagation delay to match the remainder of the rise time. But I haven't see a gate driver IC that does this, or anything more sophisticated than "pulse mode".
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Old 07-07-2011, 06:37 AM   #4913 (permalink)
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Some good news. Upped to 24v bus and larger load inductors. At 200amps the spike was +20v above the bus. Went for it and upped the gate resistors from 3r3 to 33r. Big improvement. Spike now only +3v above bus at 200amps with resultant miller knees. Time to start playing with resistors and schottkys.

i have a theory. The newer powerex cm400 modules i'm using here are much faster than the fujis i used in the car. So if they turn off faster than necessary it causes problems for this application rather than solves them. So if the switch goes off faster than than the diode can come on = problems. Need to find a balance ...
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Now, Cole, when you shift the gear and that little needle on the ammeter goes into the red and reads 2000 Amps, that's bad.
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Old 07-07-2011, 12:45 PM   #4914 (permalink)
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Well , just in case anyone had doubts , the controller really does pump 500amps
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Now, Cole, when you shift the gear and that little needle on the ammeter goes into the red and reads 2000 Amps, that's bad.
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Old 07-07-2011, 03:53 PM   #4915 (permalink)
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Held the controller at 500amps for 7 minutes this evening.
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Now, Cole, when you shift the gear and that little needle on the ammeter goes into the red and reads 2000 Amps, that's bad.
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Old 07-08-2011, 11:27 AM   #4916 (permalink)
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T minus 30 seconds
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Old 07-08-2011, 11:29 AM   #4917 (permalink)
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Quote:
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Held the controller at 500amps for 7 minutes this evening.
That's what you call 500 amps continuous.
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Old 07-08-2011, 11:33 AM   #4918 (permalink)
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T minus 30 seconds
Sad day
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Now, Cole, when you shift the gear and that little needle on the ammeter goes into the red and reads 2000 Amps, that's bad.
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Old 07-08-2011, 05:44 PM   #4919 (permalink)
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Love ya work jackbauer!
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Old 07-08-2011, 06:06 PM   #4920 (permalink)
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Here's some pics for ya Notice the nice relaxed turn off and no spike. Whats a few nano seconds amongst friends?

Held 500amps for 15 minutes today with a brick on the accelerator. Makes pikes peak look like a speedbump. Coolant topped out at 40c on the heatsink. Melted some wires on the inductor bank and boiled a gallon of water.

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Now, Cole, when you shift the gear and that little needle on the ammeter goes into the red and reads 2000 Amps, that's bad.
www.evbmw.com
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