3rd brush generator over charging ????

Crazy Horse

Well-known Member
I posted this question on the Tractor Talk forum, since it's a Farmall I'm asking about, I'll post it here as well. 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?
 
You probably need to get an additional ammeter wired into the circuit to check the tractor meter. It may be faulty.
 
As Andy indicates, the meter may be the real issue. The internal shunt in the meter can get thin and as a result the meter will read high. One quick check is to turn on the lights. if they draw more than 12 amps (assumes stock lamps) the meter is suspect. In addition, the third brush generators usually do not make more tha 18 to 20 amps on a good day. The battery condition may be a partial issue as well. A partially shorted (internally) battery acts like one with 2 cells instead of 3 this then looks like a greater load. At 3/4 throttle, the voltage across the battery should be 7 to 7.4 volts if it is closer to 8, the generator might have issues with the location of the 3rd brush. Were I working on it I would check the light draw first. then charging voltage with a analog (needle type) meter. Then that battery. Jim.
 
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
 
Original third brush setting should be set at 3 1/8 bars gap. This adjustment can be changed to achieve the correct test results.

Generator number 1100501 should be set to 20 - 25 amps at 6.9 - 7.1 volts.

Generator number 1101355 should be set to 13 - 16 amps at 7.3 - 7.6 volts
 

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