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We also had one blow up on our first robot test, However it was not connected to anything. We had mounted all the electronics and wired input power to them. Only our drive motors were hooked up. The speed controller had no motor connected to it at all. Power and pwm signal where there no motor and it blew all by itself. All the others were fine. We removed the circuit breakers for all the others just in case for the rest of our testing.
From this it looks like the controller suffered a shoot through failure - Where both the high side and low side FETs are on at the same time causing a dead short in the device itself. The circuit breakers will not protect for this type of problem, they take too long to respond to protect the FETs. This problem is usually caused by not allowing enough dead time between switching on and switching off a design issue in the speed controller.
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