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Miller Big 4D not doing so good. What to do?

JL Sargent

Diamond
Joined
Feb 7, 2005
Location
Birmingham, AL
Started a welding job with this machine today. Its a 400amp 3phase machine 10K on welding and 3.5K on outlets, 4 cyl. Perkins diesel. It has 3 transformers on shared iron. Welder was not putting out much and I noticed that one of these transformers started smoking and was real hot. I shut it down. Im suspecting that the windings in that one have shorted. Im wondering now what my options are. Get it rewound? Replacement probably would be very expensive. Could a comparable tranformer be sourced elsewhere like on EBay? Any help appreciated.
 
I doubt it has shorted out. I think you have a shorted output diode, or maybe two. That overloaded one of the windings. Hopefully its still good. Parts are no longer available and it would probably cost more to have it rewound than the machine is worth. They are not transformers but reactors.

The diodes are located in the end bell housing of the generator. Put a digital meter on diode check from base to the lead coming out of the diode. Change the ones that are shorted. Then cross your fingers.
 
Update: I checked the diodes, 6 in all, and sure enough the last one I checked (also the hardest to remove) is shorted in both directions. Maybe I will get off light and only have that to replace. Im guessing these are 60amp units. Is that right? Do you know the part number by chance. Anyway thanks for the help!
 
Assuming this is actually a Big 40D, the diodes are 275 amps at 300v. But depending on which heat sink they are mounted to they are either straight polarity or reverse polarity. Yank the diode, there may be a number printed on it.
 
50/50 chance of it being the right one. Give miller a call tomorrow and they should be able to figure out which one is needed for your machine.

920-735-4505
 
I dont think that would help since like you said some are reversed and some are not. This machine has two heat sinks. One sink passes with POS on the sink and the other passes with POS on the lead. The one I need passes with the POS on the sink. So is that straight or reverse?:D
 
OK with some scrubbing I make out 037 957B ? Ill call them a call tomorrow. Thanks with it.

The B apparently is no good. I did just look up #037 957 at the Miller website and thats the correct part # for a reverse polarity diode 275amp 300v. Looks like thats what I need. You got one?
 
Just to followup on this I talked to a Miller parts guy here in Bham thats ordering the diode for me. Nexair and Southern Welding didn't have it in stock either and this guy offered to order for $10 cheaper at $52. Hopefully will get it back together this weekend.
 








 
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