Page BottomSo i was happily welding one day, and the welder was toast the next day when i tried to use it. Turns out, one of the 4 diodes was shorted. I was rather peeved at the small size of the diodes, considering Miller said this was a 150+ amp dc welder. And them being mounted on a 2x4 inch flat plate of 1/8 aluminum as a heatsink left a lot to be desired. Plus, there was no way to leave the fan on to cool things down, with the weld power turned off. I changed all that too.
So i upgraded the diodes to 600v 300amp very low drop diodes. I scrounged them from the mud at the local metals recycling center. The #4 awg copper i used is actually an upgrade from what was in it. This is a trial fitting. You can see the white heatsink paste the diodes are mounted in.
The heatsinks are electrically hot, and there's 3 of them isolated from each other and the arc welder chassis. They are firmly held by the fiberglass perfboard. Note the bolts on the diodes are not tight yet, i replaced the common nuts with nylocks once i was happy with the layout. The lugs are soldered with aid of a small propane torch.
Here it is right side up, installed in the bottom of the welder chassis. The fan is blowing on it directly from the right. The cables come in on the left, i removed the plug/jack system, and wired the external cable right to the red 4awg i pigtailed the rectifiers with. It's mounted with 3 bolts, the rear single one floats to a large degree, this is to prevent any mechanical movement of the chassis from affecting the diode assy in any way. Because of vibration, all nuts are nylocks, most have lockwashers under them as well.
While i was at it, i replaced the fan. The new one is on the right. The circuit breaker on the upper left i had installed years ago, it's not up to heavy welding, it should be a 40amp. It's now a 40amp.
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