Farmall M...some charge, but not enough

dubv · Aug 23, 2008

Ok, you'd think the electrical system on an M would be easy enough for me to figure out..but no.
Earlier this hay season, the tractor stopped charging, so I took the generator to the parts store, they tested it, said it was dead. Sent it out, had it rebuilt.
Put generator back on, tractor still doesn't charge. Fiddle with wires, switch out voltage regulators, and get the tractor so it will charge (so says teh ammeter) when its revved up, but not at idle. Also, when the lights are turned on, it drops back down into "draw". Any ideas here? How tight does the fan belt have to be...the generator belt is pretty tight..and everything seems to be spinning well. ANY ideas would be appreciated.

rustyfarmall · Aug 23, 2008

That generator is of the 3 brush style. The third brush more or less controls just how much output the generator will have. To increase the output, the third brush needs to be moved closer to the brush right next to it.

I'm guessing that the rebuilder didn't set the third brush quite close enough. Maybe someone has a picture or diagram they could post?

dubv · Aug 23, 2008

Thank you! I will see if I can get it to someone who knows what to look for when they crack it open. NO ONE else had come up with that, but that sounds very plausible.

El Toro · Aug 23, 2008

Take a volt meter and check the charging voltage across the battery terminals. On a 6 volt system should be around 7-7.2 volts with the engine at 1/2 to 3/4 throttle. Hal
PS: If your battery is fully charged it may not show much of a charge. The rate of charge will drop as the battery is charged. Not showing a charge at idle is probably normal.

boomer22 · Aug 23, 2008

Did you polarize it after you done all the changing and fixing on it?
Are you sure the battery even needs charging?

Janicholson · Aug 24, 2008

I'll add to the discussion that if the charging voltage listed in the other posts is not happening (Below 7v) at half throttle or better, try this test:
With all things connected, battery charged over night, and tractor running, use an alligator equipped jumper wire (12 gauge is OK) to ground the F terminal of the generator. (it will not hurt anything, it causes the gen to put out max) if the voltage (and charge on the amp gauge now are in the range, the regulator is not set high enough. Adjusting them requires some substantial understanding of the parts inside, New works. JimN

Farmall M...some charge, but not enough

dubv

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rustyfarmall

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dubv

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El Toro

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boomer22

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Janicholson

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