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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I've read the threads you've suggested Steve and Neil. I wanted to make sure I am doing whatever I can to prevent reverse voltage inductive spikes from frying my controller.
I plan to have no more than 8-10A running through 30ohms/5000w dale resistor bank. I measured the inductance and it is a fraction of a mH. I will place an ultra fast 15a/600v diode (MUR1560GOS) across the bank to capture reverse spikes. Steve, you suggested a capacitor across the bank, too? How will this help more than the diode? Is it to soften the voltage rise? Will 1900uf/450v electrolytic work, or should I use a much lower capacitance?
My last linear mosfet controller was working, and one day it came on hard and stopped working. When I tested the diode I put across the resistor bank (60a/1000v) it was shorted. Some of the resistors were wire-wound Ohmites.
I also had an 18v zener from the gate to source. This one seemed ok, but the mosfets were still fried.
Registered Member #2123
Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312
You should avoid using wirewound resistors in a load bank that must switch on fast. Get some big SiC or carborundum resistors.
While on the subject, SiC schottkey barrier diodes while expensive now, may start coming down in price soon. SiC SBD's are excellent for snubbers because their Trr is faster than silicon diodes, and they can be effectively paralleled for higher current. Vf is a bit higher than FRED's, around 1 volt. Something to think about for the future.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
Yes, I did realize after the fact that using such resistors was a dumb mistake. This is why I want to make sure I cover myself better this time. Part of the learning curve...
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protecting my IGBT from voltage spikes
