Model M Electrical - Battery Won't Charge

[Kris1946A]

Hello, The battery isn't charging in my '49 John Deere M. I just had the 6-volt generator rebuilt at an electrical shop. It was tested before going out the door and works as it should. I hooked it up this weekend and the tractor started right up but the battery won't charge. It's a new battery and it tests fine. When the tractor is off, I get 6.35 volts across the battery, and when it is running I only get 6.25 volts. The ammeter, which I installed last year, is showing a slight discharge when running, which agrees with the voltage reading at the battery. I installed a new cut-out relay last year when I replaced the ammeter. I re-checked the wiring and it looks like I have everything correct. I also checked the F terminal on the generator with the tractor running and the volt meter read -0.6 v so I don't think a charge is getting back to the generator. There are no lights hooked up to the wiring. I pulled the fuse between the ammeter and the switch tonight and the glass was broken (not sure if I did that when pulling or not) but the fuse itself looked ok and not burned/damaged. I'll try a new fuse tomorrow - but my question is - would a bad fuse cause the battery not to charge? If not that - what could it be? A bad ammeter, cut-out, or switch?

Thanks for your help!

 

[Janicholson]

The charge rate in these simple systems should be about 7 to 12 amps when the battery is partially discharged, and drop to 2 amps or so when charged. If the system is not charging, the following can diagnose it. With it running, use a jumper wire to ground the F terminal on the generator (this completes the field circuit and makes a good generator charge to its adjusted max. The amp meter should reflect charging. The cutout in these has 2 components one that connects and disconnects the generator so it charges when running above idle, and stops charging when shut off or slow idle. The other part is a simple resistor to ground. This resistor is the path for voltage to travel through the field windings to ground. The cutout relay, and the generator must be grounded (clean shiny metal) to complete the circuit. John T has a solid JD history and his trouble shooting info is in the archives here. Search John T charging for the info. Jim

 

[John T]

Thanks to Professor Jim for the reference. If original the M (POS Ground) used a 2 terminal (BAT GEN) Cutout Relay and a Manual Low High light switch charge control system.

To be on the safe side, especially if the genny has been to a shop, be sure to Polarize the genny BEFORE start up. Once running if you use a jumper wire to momentarily jump the Gennys FLD post to ground to see if it charges ????????? If it charges then but NOT otherwise, that tells me the genny itself is okay so the Cutout Relay may be bad orrrrrrrrrrrrr Not well grounded orrrrrrrrrrrr The light switch is bad or not well grounded orrrrrrrrrrrr The wires missing from FLD on genny up to light switch.

Ive seen many of them with a good genny NOT charge because the light switch or cutout relay isnt well grounded or the switch is bad.

Polarize,,,,,,,,Try to ground the gennys FLD post,,,,,,,,,,Insure Relay and Light switch are both well grounded,,,,,,,,,,,insure the wire from FLD up to ligth switch is in place

Work through my Troubleshooting Procedure for a Cutout Relay system

SURE check the fuse also but that is likely NOTTTTTTTTTTTT the problem you describe..

https://www.yesterdaystractors.com/cgi-bin/viewit.cgi?bd=ttalk&th=2060825


John T
John Ts Charging Troubleshooting

 

[John T]

See Link

https://www.yesterdaystractors.com/cgi-bin/viewit.cgi?bd=ttalk&th=2060825
John Ts Troubleshooting

 

[John T]

I cant get the URL to link ??

John T's Troubleshooting

https://www.yesterdaystractors.com/cgi-bin/viewit.cgi?bd=ttalk&th=2060825
Clik Here

 

[Kris1946A]

Guys, thanks so much for the troubleshooting procedures! I'll try them out as soon as I can and keep you filled in.

 

[M-MAN]

You didn't mention polarizing it. That's a must. The fuse was still good or it wouldn't have ran.

 

[Kris1946A]

Hey guys, thanks very much for the input and troubleshooting. Here's the dumb mistake I made when I made all the connections last year - I never grounded the cut-out relay. So, after I went in today and grounded it, the ammeter is on the right side of the dial when running, and I'm getting 7.5-7.8 volts across the battery when running on high charge, a little less on low charge. I think I'm in business now!