Battery Charging Sporadic on 881

Hi, the charging system on my Ford 881 is acting up. It has the original setup with 6volt generator with positive ground. The charge light on the dash periodically comes on, indicating that the generator is not charging. I confirmed this with a voltmeter showing only 6.7 volts at the battery whether it is running or not and regardless of rpm. When the indicator light is off, the volts at the battery is about 7.6-7.75.
I noticed the indicator light was on one night when the tractor had been running for hours. The next morning, the light was off when starting the cold tractor. Later, the light came back on. I tried switching off and restarting, but that never seemed to help. The wiring is relatively new and connections tight. Seems like if I let the tractor sit and get cold, it will start working.
Then an odd thing happened the other day when I had been using the tractor for a couple hours with the indicator light on: I accidently pressed the starter button BEFORE I turned the ignition key to start the tractor (meaning the tractor turned over as soon as I turned the key). Now the indicator light had gone out and the tractor was charging. It didn't do this the multiple other times I had shut down and restarted the tractor normally. Does this suggest the starter switch is the problem? I am not good with electrical stuff, so please bear with any dumb questions. Not being sure how to check the charge coming directly off the generator, I didn't try that because I didn't want to fry something, including the newer voltage regulator. Thanks!

Educated guess from available information: Generator brushes or VR contacts.

Dean

Intermittent problems like that are difficult. It could be something going open in the generator when it get warm or the voltage regulator acting up when it gets warm. The next time it happens, try tapping on the V.R. with the handle of a screwdriver and see what happens. You could do the same with the generator too. If you have an auto electric shop nearby, you could take the generator and V.R. to them and have them checked, but be sure to tell them the whole story, or they guy will just test them cold and tell you they work. I don't want to see you start throwing parts at it, but from my experience lately with new voltage regulators I would suspect that.

I forgot to answer your last question. The next time it fails, hook your voltmeter up, set on 20 volts or whatever it says, negative lead to the large post on the generator marked A or ARM and the positive lead to a clean ground and see if you are getting 7 or so volts from there. That will tell you if the generator is putting out.

Thanks for the reply Jim, and the explanation for measuring the generator voltage.

Thanks Dean

Be advised: Do not try to use an inexpensive DVM to diagnose an OEM vintage Ford charging system on anything but battery voltage.

Use a vintage analog VOM (mechanical meter type) if you can find one.

Dean

Having said all that, if your diagnosis indicates that you need (and want) a replacement generator, I have several rebuilt 6V generators for 55-64 Ford tractors (not diesels) that I have decided to sell as I have sold all but two of my vintage Fords. Recently, I have sold two but have 3 or 4 more.

Dean

Thanks Dean! I'll let you know if I need a generator.

I just have a non-analog voltmeter. I'll have to look around for a different one.

yea, I forgot to mention that voltmeter thing. You get some wild readings using a digital meter due to the ignition induction.

Dean,
Looks like I need a new generator. Output on my old generator is 2.3 volts. You mentioned having a few that you are selling. I'm interested. Let me know how to contact.
Thanks!

(quoted from post at 17:08:13 11/14/19) Dean,
Looks like I need a new generator. Output on my old generator is 2.3 volts. You mentioned having a few that you are selling. I'm interested. Let me know how to contact.
Thanks!

Click to expand...

hile you are measuring that gen Arm voltage, momentarily jumper Arm to Field to see if voltage increases above 2.3v

Don't overlook the obvious either. How's the belt and tension?
Simple and free to check.