Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Paul & Sabrina's cheap DIY 144v motor controller

MPaulHolmes · 07-28-2010, 09:59 PM

At around 500amp, there is a voltage spike of around 15 or 20 volts from drain to source. So, if there was even the TINIEST throttle while the contactor was open, it would immediately drive the pwm to 100% duty. And with a motor that's not spinning, it's almost a short circuit. So, you would have maybe 2000 amps or even more for a very short instant, and the voltage spike from 2000 amps would be more like 80 volts instead of like 20 volts. That's because the voltage spike is proportional to the current. So 4 times more than 500 amps would have 4 times the voltage spike. So, if you had 120v nominal, that would put the total voltage (counting the spike) over 200v, which would short all of the mosfets.

Another way to test if this is what happened is to measure the resistance of the potentiometer at the instant that the pedal contactor closes/opens.

07-28-2010, 09:59 PM	#3603 (permalink)
MPaulHolmes PaulH Join Date: Feb 2008 Location: Maricopa, AZ (sort of. Actually outside of town) Posts: 3,832 Michael's Electric Beetle - '71 Volkswagen Superbeetle 500000 Thanks: 1,362 Thanked 1,202 Times in 765 Posts	At around 500amp, there is a voltage spike of around 15 or 20 volts from drain to source. So, if there was even the TINIEST throttle while the contactor was open, it would immediately drive the pwm to 100% duty. And with a motor that's not spinning, it's almost a short circuit. So, you would have maybe 2000 amps or even more for a very short instant, and the voltage spike from 2000 amps would be more like 80 volts instead of like 20 volts. That's because the voltage spike is proportional to the current. So 4 times more than 500 amps would have 4 times the voltage spike. So, if you had 120v nominal, that would put the total voltage (counting the spike) over 200v, which would short all of the mosfets. Another way to test if this is what happened is to measure the resistance of the potentiometer at the instant that the pedal contactor closes/opens. __________________ kits and boards Last edited by MPaulHolmes; 07-29-2010 at 12:49 AM..