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View Full Version : MIG plus Generator = Problems



torchroadster
06-29-2008, 08:15 AM
I tried to run my 120V MIG welder off my 5000 W generator yesterday and the motor that feeds the wire either wouldn't turn or would turn very slowly - even with no load.

The MIG works fine on house power.

I use this same generator routinely to power an air compressor, air conditioner, fluorescent lights, drill motor, etc. without any problems.

I measured the no-load voltage of the generator at 128V. I have no way to look at the waveform.

Any ideas on what's going on and if there is a simple fix?

japcas
06-29-2008, 11:39 AM
I picked up a used Coleman Powermate 5000 watt generator for $45 because the guy that owned it couldn't get it to run. It had been to a shop once before and they got it to run but shortly after he got it back he couldn't get it started again so he wanted to get rid of it. Anyway, it looked like new so I brought it home and checked it out. The carb was clogged up and with a little cleaning I had it running. I rigged up a load bank with some 1500 watt heaters to check rpms and hz cycles. After about 1500 watts were applied to the generator, it would start to slow down, which in turn makes the hz slow down also. It turned out that the shop that worked on it didn't set the governor linkage up right and the engine was unable to maintain speed. I adjusted the linkage and set it so that you could load three 1500 watt heaters on it, a total of 4500 watts, and the generator wouldn't even begin to slow down. You could hear a noticable change in the exhaust note as the engine began to work harder, but the rpm remained steady as it should.

Don't know how the circuitry on the mig welder works, but it may be that the power of the genset is outside of it's operating parameters. It may have a safeguard built in to prevent it from running on power that is out of spec? The other tools that you listed that run on your genset aren't very picky about the type of power that they are fed. Which is why they probably run on your genset.

jcarter
06-29-2008, 11:49 AM
If you have access to a meter measure the frequency. If you don't have a meter that measures frequency make sure the engine is running at 3600 rpm.It sounds like it may be running a little fast if it is producing 128 volts.

wierdscience
06-29-2008, 12:03 PM
From experience most welders will tolerate +/-%10 in both frequency and voltage.

I would checkout the gensets panel wiring particularly the ground for an open.

Oh and simple way to check frequency is a plug in clock and a stop watch.

macona
06-29-2008, 05:29 PM
You need to check the voltage with a load on it. Best guess is the generator is too small.

torchroadster
06-29-2008, 07:14 PM
I will try to check the frequency, I think my DMM has that function.

I'm pretty sure I wasn't overloading the generator - it's 5kW and I wasn't welding just trying to feed the wire so the load would have been minimal. I was able to strike an arc but with no wire feed it didn't last long!

Dunc
06-29-2008, 10:38 PM
Others have addressed the load, the voltage & the frequency. I know nothing in an engineering sense but I have read that the output may not be a sine-wave but closer to a square-wave. I am further guessing that the heavier the load the more the waveform strays.

The clincher of course... does this make any difference? I don't know but I am throwing it out there. Hope someone can enlighten me.

rdfeil
06-30-2008, 12:54 AM
Others have addressed the load, the voltage & the frequency. I know nothing in an engineering sense but I have read that the output may not be a sine-wave but closer to a square-wave. I am further guessing that the heavier the load the more the waveform strays.

The clincher of course... does this make any difference? I don't know but I am throwing it out there. Hope someone can enlighten me.


Dunc,

Just FYI any rotating generator will produce sine wave power. The frequency is determined by the number of poles in the generator and the rotational speed. The voltage is determined by the exciter (think field in an old car generator) current and the load (within the design limits of the windings).

An inverter or DC to AC converter is another animal which often is not true sine wave output. This might be what you are thinking about.

Robin