I have an old Miller Big 40 with: serial#: U504404 and stock#: 900955 stamped on the front control panel. Other than that, the engine is a F163 with numbers 4274 and 959534 on the engine plate.
The unit had been running fine, idling at 1850, and putting out good voltage. I moved it about 40 yards after it had been sitting a month (its on a trlr) and it didn't work after that. I chased the wires and it has voltage (about 60+) up to a "transformer-looking-apparatus". No opens, shorts, burnt wires, or problems anywhere else; not the diodes, not the slip rings or brushes. This "transformer" is connected to #19 and #20 wires by metal blades sticking out of the wrap. #19 and #20 are 00 gauge wire. This "transformer" is large and made of what looks like a 5" wide strip rolled up - not single strand wire. There is power up to this "transformer", but not after. The 00 wire coming from the diodes is tagged #19 and has power, the 00 wire going to the positive electrode stud on the front of the engine is tagged #20 and has no power. According to the most accurate wiring diagram I could find from Miller, it refers to this "transformer" as a shunt, and nothing else. It doesn't look like any shunt I have ever seen, but then again I wasn't alive 30 years ago, let alone 50+, which I estimate the unit to be. I am trying to figure out just what this thing is and if I need to replace it. My thoughts are that, if it is just a shunt, I can eliminate it as i have no meter. Any help would be much appreciated.
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03-18-2011, 01:44 PM #1Junior Member
- Join Date
- Mar 2011
Old Miller Big 40 welder won't weld, help