Capacitor and resistor to prevent voltage spikes to the diodes

Tue, 31 Aug 2021 15:28:16 GMT

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Hello,I have a Westward 115v wirefeedwelder (fluxcore). The output was 75 amps but I toasted a diode and decided to upgrade the heat sink and diodes from 50 amp units to 75 amp units with fan cooled oversized finned heat sinks. I have read that voltage spikes can quickly ruin the diodes, and a resistor and diode should be used across the output to absorb any destructive spikes. Can someone kindly give me some specifications on the capacitor and diode I need to use? I believe the voltage output is 30 volts or so dc at 100 amps or less now.Thank you so much!
Reply:Most diode arrays are protected by a simple and inexpensive device called a “Varistor”.   I believe the potential voltage spike produced by breaking an arc is relatively small.  I would also wager a bet that a suitable varistor could be salvaged from an inexpensive household surge protector.   On the other hand; cheep low PIV (peek inverse voltage) rated diodes are most vulnerable to damage from voltage spikes.
Reply:An Airco welder used .01 disc capacitors at 1000 volt rating across all diodes.I used that value on my dc converter box..You can go up to 85 amp diodes, they use the same stud size..Use the highest voltage that you can find.I have found diodes badly under rated in some welders.One welder I repaired claimed 140 amps DC output,It had 2  85 amp diodes in it.I think that you can get voltage spikes went the arc breaks because theres a choke coil in the circuit.Many dc welders that are left plugged in get shorted diodes from lightning strikes on the power lines. I have a Miller 130 mig and will check the book when I find it.I do not leave it plugged in.

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go to see Welding Machine for Capacitor and resistor to prevent voltage spikes to the diodes