Farmall H cutout question Yet

I think the problem may be the generator. I thought it was OK because it charges 13 amp at full throttle when cutout is closed or when by-passed and jumped bat to armature. The generator was on a shops test stand a few yrs ago and he said it was OK after new brushes, (approx. 3-400 hrs. ago). It's only generating less than 1 volt testing armature to ground when cutout blocked open and that won't close the cutout. Also, it wouldn't charge when putting an inline diode in the circuit instead of the cutout. I used a digital and an analog meter to test. I thought I understood the generation system and I had or I have tried the things suggested by Jim, John,Pete & Gene. I would appreciate any thoughts on why the low voltage output when it will charge 10-13 amps. I think it to go to a shop again. Thanks -- wok

Generators start their output while disconnected. (cutout) the field windings are attached to ground on the F terminal (through a switch for Low High output) the other end of the field circuit is connected to the output brush (or a third brush on that same side). The output from the armature goes through a grounded brush and the ground of the generator housing to the tractor.
As the armature begins to turn, the field has near no volts in it. The field windings are wound around iron cores. These iron cores hold magnetism (iron can be magnetized) this magnetism affects the spinning armature by creating electricity in the armature. This fresh electricity has only one path to ground and that is toward the ARM terminal through the non-grounded brush. Because the field input is connected there, the voltage goes through the field then to the F terminal and finds ground through the control switch (or voltage regulator). This fresh field voltage raises the amount of magnetism in the field. This causes an increase in the voltage produced in the armature. This then adds to the field circuit voltage and current. Raising the armature output. When the armature output voltage reaches a little more than battery voltage, the cutout pulls in and starts charging the battery. (this whole process might take 1/2 second) Inside the cutout, there is a pull in winding that "feels" the output voltage. These are fine wires. Once the current flows out to the battery, the hold in windings (much fatter with full output amps passing through them, hold the contacts closed. When the engine slows so much that the battery voltage exceeds the gen output, that hold in current is reversed, and overcomes the pull in winding effort, and opens the contacts.
Low or no output with field grounded means either the field circuit is open, or the armature is not putting out. Jim

Wow....Jim....Your one smart cookie! Can I hire you to come fix all my charging sytems...with generators? Good job

Jim --Thanks for the explanation. If the field is open or the armature isn't putting out why does the generator still charge 6 volts & 13 amps when armature to battery is is connected via jumper or the cutout closed? The diode connection (correct flow) suggestion didn't work because of the same possible problems? -- wok

Intermittent issues are tough to deal with. With the wires removed from the generator, do the following. With a piece of plastic (strip of butter tub cover) under the grounded generator brush, the field terminal should show no conductivity to ground, and between 2 and 4 ohms from F terminal to A terminal. If these are not met, The generator needs rebuilt. You should only be using an analog meter, not digital unless it is very high quality pro level. Other digital meters do not accept the spike filled electricity found in old generators. The diode used must be a 20 amp power diode, not an electronic device. Jim

NICE explanation by Professor Jim.............

I will only add the open unloaded output voltage of a Generator is easy to achieve and will be much higher then what happens when its connected to a load, that's when it takes more energy and a good generator. What really counts as to the quality of a generator is what voltage it can raise battery voltage to THATS THE REAL TEST. If you dead ground the field that forces the genny into it high charge state and if it still cant raise battery voltage the genny is likely bad.

The ground the field test and the motor test described in my Troubleshooting Procedure an help find the cause of non charging

http://www.ytmag.com/cgi-bin/viewit.cgi?bd=jd&th=458743

John T
John Ts Charging Troubleshooting

What I have run into different times is that a generator won't charge so you polarize it, (that amounts to the same to the generator as manually closing the cutout points) and then it charges. Next time, no charge again. Often caused by poor brush contact due to incomplete removal of the mica between the bars on armature. Very common in rebuilt units. They make a slice down the middle of the mica but don't get right to the edge so brush touches the mica but once you excite it so to speak it will work for a while.

INDEED if the mica segment between the commutator bars isn't properly undercut you can get brush bounce and poor electrical contact..........Turning down the commutator is only half the job lol

John T

Another cause for not charging until you polarize the generator each time you use it is poor a ground of the regulator or poor connections in the field relay circuit in the regulator. You can check this by measuring the voltage on the generator F terminal after starting the engine and before the generator starts to charge. If you have more than about .1 volts on the F terminal you have a grounding problem