Hi,
So Im working on what is basically a fancy capacitor discharge welder, and I keep frying the mosfets so they get stuck on.
Everything works perfectly at low voltages (~12V) but only for a few times then the mosfets are stuck on and no longer function as switches. Ive gone through so many of these things its time to ask for help.
Attached is a wiring diagram of the power circuit. the lower part is the driver/mosfet/capacitor bank I'm having trouble with, I included the top circuit (which is just a way to sense head contact for the controller) just in case it's causing something funny to happen.
Basically the weld head comes down, both electrodes make contact with the metal, then after a short dwell period the caps fire for about 300us.
The resistance of the weld head/ and wires is very very low so I made a .05 Ohm "resistor" out of resistance wire used in heaters which I confirmed to be ~.054 Ohms. I originally had 12 mosfets in parallel but after a few failures doubled down and put 24 but they still fail closed at the same voltage level so I don't think it's a current problem.
I'm thinking maybe there's a voltage spike which is killing the mosfets but have no way of measuring it and they die when the capacitors are only at 15v so it would have to be a big voltage spike... I also might just be doing something obvious and dumb lol
Any ideas or pointers would be greatly appreciated!
Thanks guys!!
So Im working on what is basically a fancy capacitor discharge welder, and I keep frying the mosfets so they get stuck on.
Everything works perfectly at low voltages (~12V) but only for a few times then the mosfets are stuck on and no longer function as switches. Ive gone through so many of these things its time to ask for help.
Attached is a wiring diagram of the power circuit. the lower part is the driver/mosfet/capacitor bank I'm having trouble with, I included the top circuit (which is just a way to sense head contact for the controller) just in case it's causing something funny to happen.
Basically the weld head comes down, both electrodes make contact with the metal, then after a short dwell period the caps fire for about 300us.
The resistance of the weld head/ and wires is very very low so I made a .05 Ohm "resistor" out of resistance wire used in heaters which I confirmed to be ~.054 Ohms. I originally had 12 mosfets in parallel but after a few failures doubled down and put 24 but they still fail closed at the same voltage level so I don't think it's a current problem.
I'm thinking maybe there's a voltage spike which is killing the mosfets but have no way of measuring it and they die when the capacitors are only at 15v so it would have to be a big voltage spike... I also might just be doing something obvious and dumb lol
Any ideas or pointers would be greatly appreciated!
Thanks guys!!
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