How does it get excited? Miller Big 40

Tue, 31 Aug 2021 13:59:22 GMT

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Hi All,I have a Miller Big 40 that isn't putting out any  voltage at all. None at the 110AC outlet and none at the leads. The brushes seem to be contacting the armature evenly, the alternator seems to be working ok, the idle lock out control is working properly, the two little black rectifiers check out with an ohm meter but the mov or capacitor on the one doesn't look healthy but it doesn't read shorted with the ohm meter, all wiring looks to be in place and serviceable. I haven't used this welder in several years. I bought it for my dad several years ago and at that time it worked fine. He passed away just over 5 yrs ago and it hasn't been run since. It sits in the weather so as you might expect the gas tank was trashed due to water. The carb had to be taken apart and cleaned and the points need a pass or two with the ole fingernail file but she starts and runs great, just no power out put at all. Any helpful hints or suggestions would be greatly appreciated.Thanks In Advance,TR Ganey
Reply:You might want to hear from "Weldersales". He can likely steer you in the right direction, good luck.City of L.A. Structural; Manual & Semi-Automatic;"Surely there is a mine for silver, and a place where gold is refined. Iron is taken from the earth, and copper is smelted from ore."Job 28:1,2Lincoln, Miller, Victor & ISV BibleDanny
Reply:OK, you'll have to flash the fields:1) open right side door2) Disconnect leads #5 & #6 from SR1 (one of the 2 small square "bridges") note the way they came off the bridge as you'll have to put them back on in the same position3) Attach some jumper leads to a good 12Vdc battery red + black -4) Start the welder's engine5) Momentarily touch the + jumper to lead 5 and the neg jumper to lead #66) Shut her down and reattach the leads back to SR1 There ya go......JeffMiller tech
Reply:Restart the engine and check for output, If it's still not working just repost.
Reply:Thanks Jeff,I'll try it first evening I get home before dark and it's not raining.TR Ganey
Reply:Yes flashing the field. They need to have a residual magnetism in to start up. When left sitting for long periods the magnetism fades to nothing so no excitation at startup.
Reply:Finally had a chance today to "flash the fields".  I tried it a couple times with no results. I could see a very, very small arc when i would touch the positive wire. Seeing how the welder was no use as is I decided to take chance and expand on the advice given. I plugged in a small grinder to the 110v outlet and when I would touch the positive wire it would turn very slowly. Then I would stop the motor and hook the wires back up but it still wouldn't weld and still no out put at the 110v receptical. Expanding a little further on the original advice I decided to try flashing the fields while the wires were still on the rectifiers with the grinder plugged in and turned on. After holding the external voltage on the wires for appx. 3 seconds the grinder took off full speed! Now the welder will weld. I melted a couple rods just to warm everything good then tried the idle circut. For some reason it wasn't getting enough voltage at idle to cause it to rev up. If you flipped the switch to auto idle and then struck an arc before the engine idled all the way donw it would rev back up but if you let it come all the way down to idle it would not rev back up. I was out of time because of a meeting I had to attend so that was it for today. On the way home from the meeting I believe I may have figured out why it would not rev up from an idle. While working on the engine and carb. I had idled it down lower than normal. As soon as I have a chance I'll idle it back up to specs and see if that cures the problem. Thanks for the advice!TR
Reply:Idle is at around 37-42HZ, with high idle at 61-62 Hz unloaded, yes welders are set by frequency in a welder that has AC auxillaries, NOT by actual engine rpm.Tested at your auxillary receptacles
Reply:Thanks, I'll check it out and adjust accordingly one afternoon this week and post the outcome.TR