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Old 04-06-2011, 07:36 AM   #4601 (permalink)
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Originally Posted by adamj12b View Post
Which end they stick out is your decision. Some layouts of the car work better 1 way instead of the other. It does not matter.

If you want, you can use a longer B+ bar so you have the B+ and B- on one side, then B+ and M- on the other. I dont think ive seen one like this yet though....

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.)

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