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Old 04-06-2011, 07:51 AM   #4603 (permalink)
adamj12b
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EVVette - '71 Chevy Corvette Coupe
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Quote:
Originally Posted by DJBecker View Post
That configuration wouldn't be balanced.

The layout should be based around equal path length. The current shouldn't have an easier path to some devices.

This requires that the motor connect to opposite ends of the controller. Otherwise the freewheel current will mostly prefer the "close" diode. When that burns out because it's carrying all of the current, the current will prefer the next device and burn that out in turn.

That is if the device burns out. Sometimes diodes fail by shorting out. When the controller only has a motor current sensor, it can't detect the case when a freewheel device shorts out. Instead it does the opposite of protecting itself. Since most of the battery current flows through the short instead of the motor, it increases the drive PWM in response. And keeps increasing it until every push-side device is destroyed.

(We've replaced all of the push-side MOSFETs only to have them immediately blow up in a spectacular way with the first test. Twice. We now remove and test every diode after any power section failure.)
Good Point.

I was not thinking of that when I rattled off that post.

-Adam
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