3rd brush generator overcharging ????

I've got a Farmall A with stock factory wiring, all rewired with new wire and terminals. Everything is wired properly with the correct-size wire and size #1 battery cables with good terminals. Six-volt positive ground, third-brush generator with a working cutout relay on the generator case. Charge control is done through the IHC type 4-position light switch on the dash (controled charge, full charge, full charge with dim lights, full charge with bright lights). My battery is a bit iffy and shows only about 5.7 volts when sitting while the tractor is not running. It has enough oomph to start the old girl but not much more.

So here's my problem. Once the tractor fires up, the charge rate is much too high even on the first "charge controlled" position of the light/charge control switch. At anything much more than idle speed, it pins the amp needle to +30 amps. At idle it drops to about 26 amps, still too high. Moving the third brush to different locations inside the generator has no effect on the charge rate, too high no matter where the third brush is positioned. When the tractor is running, the battery keeps its low 5.7 Volt reading.

Any suggestions as to what might be causing this? I'm getting a ton of amps, seems like the voltage isn't up to par. Should the battery not be showing something like 6.5 volts or more when the tractor is running? How about the excessive charge rate, any suggestions?

I don't know the setup on the farmall 3rd brush gen. but on the ford 3rd brush gen. the gear train could get out of mesh and all the turning in the world would have no effect on the gen. output.In your case it might be worth a check.

If the battery is okay it would read around 6.3 volts if fully charged. That 5.7 indicates a bad or very low battery and there may be a short causing excess current draw when attempting to charge. The further the third adjustable brush is moved from the fixed brush the less charge. The charge control resistor portion of the LHDB light switch should read around 2 to 4 ohms in the Low charge position but near 0 ohms (dead ground) in High charge. In the event the genny or wiring (FLD on genny up to switch) had a problem such that the gennys FLD post is shorted to ground, that would cause a constant high max charge.

John T

The gear train? Not sure what you might be referring to.

While I'm not an electrical person something I learned a long time ago is if battery is low the genny will make lots of amps trying to bring battery back to where it should be. Another thing that could be tried is taking genny in for testing to be sure if is working correctly.

(quoted from post at 15:28:21 07/03/15) The gear train? Not sure what you might be referring to.

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Attatched to the screw is gear that meshes with a rack connected to the third brush.If not meshed no action when turning the screw.

Wondering if the amp gauge might be giving a false reading. Showing 26 amps at idle? Is a generator capable of that?

If you turn on the lights with the engine off, does the amp meter agree with what a typical lighting load would be?

Attatched to the screw is gear that meshes with a rack connected to the third brush.If not meshed no action when turning the screw.[/quote]

OK, I think I get it ..... the gear is for moving the 3rd brush. This set up is a bit simpler but the 3rd brush is moving with no result.

I see a few problems. First off the battery doesn't get to 6v much less the 6.2 to 6.5 it should be at so you know it's bad. Second, the genny is incapable of putting out 30 amps so you know that's false. It is capable of a 30 amp discharge so you may want to switch the leads on the amp gauge. They are backwards now. Lastly your genny needs rebuilt. Moving the 3rd brush always changes amp output if it's good. Don't forget to re polarize the genny. The only way you can have amps coming out of the genny and not raise battery voltage while running is no connection somewhere from the genny to the battery. Good luck and please post a follow up.