M Charging Issues

I think I know the answer, but since I am relatively new to the Green and Yellow side of life, I thought I would ask and make sure!

I am seeing about 5.5 volts at the battery when the engine is running 3/4 throttle, switch at high charge. However, at low charge, same engine settings, the meter flickers to -12, as high as sometimes -4. The generator is polarized, no internal grounding, new brushes. Positive ground.

I'm leaning towards the switch being defective, since the relay seems to be in decent shape.

Am I right or is there something unusual about Deere M series charging systems?

Ben W.

Its nothing unusual, its 6 volt Positive Ground with a simple Cutout Relay and a Low High Charge control switch system that the gennys FLD post wires to. See how she charges if you momentarily jump the FLD post to ground?? If she charges fine then but not otherwise,,,,The Low High charge switch is bad,,,,,,,or,,,,,,,,,,,The LH switch isnt well grounded,,,,,,,or,,,,,,,,,,,the wires open from FLD on Genny up to the LH switch.

A good charged battery should read around 6.3 volts just sitting there engine not running, but if coupled to a good working genny at high RPM the battery voltage should rise to at least 6.5 up to 7 + volts. That 5.5 sounds like a bad genny and/or mis wiring or a short.

On HIGH charge the wire leading to the Gennys FLD post should be an effective dead short to ground and at Low charge approximately 3 or so ohms is inserted between frame ground and the FLD post. If the LH switch isnt well grounded, that can cause non charging since theree no current path for field current INSURE LH SWITCH HAS A GOOD GROUND

You can bench test the Genny using my Motor Test in my URL link below. For a detailed step by step troubleshooting procedure for non charging run through it and post back any questions

John T
John Ts Troubleshooting

You aren't charging at all so full ground the field & check the voltage/amps from the genny first. 13 amps is the max for your genny. The 3rd brush is how you adjust the amp's. Try cycling your switch several times as well.

Thank you John!

I've always had your instructions printed off in my shop. I had worked through it before posting.

The only thing I hadn't checked off your list was the motor test. Did that this afternoon: the generator motors good when the field is dead grounded, but does nothing when the field is disconnected. The jump does spark at the ARM, but it doesn't spin it.

Fields?

Ben W.

Yep if it fails to speed up when the Field ground is removed they are bad, maybe shorted out or open (esp where the 2 splice in middle). She cant charge unless BOTH fields are good, continuous, not shorted to case and the grounded at the FLD post

John T