Quote:
Originally Posted by apowers
Paul
Is there any reason why the controller should have power on first?
I have not gotten the new controller installed yet and I don't want to mess it up.
Thanks Alvin
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I think it's just good practice. If there is a failure in the controller, the controller can evaluate this before closing the main contactor and report the fault. I think paul's code checks for current in the motor loop before enabling PWM output. If the controller has failed 'on', you'll have some current flowing through the precharge resistor into the motor loop. Another option, though more complicated hardware-wise, would be to measure the cap voltage and close the contactor at an appropriate level (or dV/dt?).
Otherwise, since failures in the 'ON' condition are common, you could directly connect your pack to your motor when your contactor closes and either overspeed it if it's in neutral or, worse, run into something.
I have my voltmeter set up to read the controller voltage to manually accomplish the voltage measurement. When the breaker is closed and the caps precharge, you can watch the voltage rise. When it's reasonably high, I close the main contactor and drive. If the controller has failed, the caps wouldn't charge at all and I'd know something is wrong before closing the main contactor.
All this being said, I've accidentally not followed this practice on occasion while beta testing this controller and turned the controller on after precharging. Also, since the caps take a while to discharge, I almost always turn it off while there's high voltage across the caps (though the contactor is open).
So far, no problems.