HELP JMOR AND SOUNDGUY

(quoted from post at 15:47:35 09/02/14) I'm helping friend work on his MF35, 12v gennerator, it stopped charging. I Need a refresher course. Looking at the VR diagram, it appears the VR grounds the fields to charge. Too much current, the current/voltage relay on the right picks up, installing a resistor to limit current
[b:9b94596749]Do you have 4 terminal VR like the dwg of my combine that you posted? Is it a Delco generator? If yes & yes, then so far, so good.[/b:9b94596749]


1. Am I right so far?

The gennerator is self exciting, requiring no voltage applied to the Armature.

2. Correct?[b:9b94596749] residual magnetism generates start up field current from arm, so yes to self exciting.[/b:9b94596749]

3. So if the VR is defective, then all I have to do is remove the field wire and short the field to ground and ammeter should show charge?[b:9b94596749]If it is of this type where VR provides gnd to field (type "A"), yes, but you don't even need to remover field wire from VR to gen, just ground it.[/b:9b94596749]

I wired this tractor about 3 months ago. It has worked up to now. I ran a ground wire to VR and Genny.

4. If I got a yes on questions 1,2 & 3, then it a good chance in need to replace VR. I've forgot how to polarize the VR. [b:9b94596749]Two (2) things have to happen in the VR in order to make a good generator charge, 1) the field contacts need to provide the generator with a field ground, 2) the cut out contacts need to close so as to connect gen to batt. So if you want to bypass VR functionS, jumper Field to gnd AND jumper ARM to BATT while running. We don't actually polarize VRs, just generators (where the magnetic poles live) . Done by applying BATT voltage to ARM, where it passes on thru to fields and on thru VRs field contacts to ground to complete the circuit[/b:9b94596749]
[b:9b94596749]If you have a type "B" gen instead of the type "A", then that is a whole new story.[/b:9b94596749]


If I got it all wrong, please give me a refresher course on trouble shooting a genny while on tractor. The brushes look good, communtator looks good, all wires look good.

Thanks,
George

Click to expand...

(quoted from post at 14:12:10 09/03/14) Yes, the magnetic force was with me. The generator's resistance measured 70 ohms from Arm to ground and Field to ground. It was so rusty, I installed a wire to the place the armature brush was grounded and ran it out the end of genny. Then the resistance dropped to just a few ohms. I had put ground wires on everything when I rewired it a few months ago. Who would have thunk there was so much rust it would caused a problem?

After shorting out fields, genny put out, but it need a new regulator.

MISSION ACCOUMPLISHED.
Thanks Jessie and Soundguy,
George

Click to expand...