Farmall H Generator

[MarkinOhio]

This is on a 1949 H, magneto ignition and the original 3 brush generator with a cut out, no voltage regulator. Charging had been erratic for quite some time and finally quite completely a few weeks ago. I just got it back this afternoon after a complete rebuild. The cut out relay was bad and the armature was shorted. New brushes, armature, bearings, and cut out relay. It charges just fine on the test stand but not after I installed it back on the tractor. The field wire from the generator to the switch not shorted or open. The other wire from the generator to the ammeter is also good. All lights work both dim and bright and the ammeter shows about a 10 amp discharge with the lights on bright so I know the ammeter is working. The field resistor on the light switch shows about 3.1 ohms across it with the field wire disconnected. This is where I got lost. With a jumper wire connected directly from the positive ground cable of the battery, through my multimeter, and to the grounded terminal of the field resistor Im getting no continuity. It sure seems like I should be getting a direct short from the grounded end of the resistor back to the battery. Also there is no continuity from the bare metal light switch to ground. Should there be? The metal switch housing is grounded but not real sure if the cover that the ammeter and switch are mounted to are making good contact with the housing. However the way Im checking things it shouldnt really matter. Sorry for the long post but I wanted to make things as clear as possible.

 

[charlieu]

I can't tell you what you are doing wrong with your meter. I can tell you that the L and H position (first and second position of the 4 position light switch) is what controls the output of the generator by control the ground for the field windings of the generator.

The switch needs a good clean connection to the box cover and the box cover must make good contract with the light switch box

The box must make good connection with the steering post and the steering post must be grounded with the transmission cover.

When the light switch is in the 1st position (L) field current passes through the resistor.

When the switch is in the (H) position the resistor is bypassed and the F wire gets full ground making the generator produce maxium output, about 11 to 13 amps. at high idle speed.

 

[MarkinOhio]

Charlieu, first of all thank you for your quick response. What you described is exactly how I know that the 4 position light switch is supposed to work.
Im very suspicious of my cover having a good ground to the light switch box and will get everything cleaned up tomorrow. The box itself is well
grounded to the steering post and the post is well grounded to the transmission cover. What I failed to check was the grounded end of the field
resistor connection to the light switch itself. Again Ill do that tomorrow and report back.

 

[Janicholson]

The part of the light switch connecting the field to ground uses the switch body as a ground. that uses the box, that uses the post, that uses the post mount. Each of those are subject to rusting and failed connection, or paint and failed connection. The switch is only through the resistor in L position. In all other positions the generator is running at maximum output. H to help charge when starting and stopping a lot. And D and B to keep the lights on. A workaround is to put a ground wire from the switch mounting hole (sanded and shiny) to the tractor frame (clean and shiny). This prevents needing to look for failed rusty connections that appear good. to test the generator, just ground the F terminal. it should charge nicely as though in H,D,or B. Jim

 

[used red MN]

One thing I will add, probably applies if every part of the machine is well painted or if it is just an as is ..work clothes.. type. Make sure the generator case has a good ground path to the engine. Also make sure the cut-out also has a good ground to the genny case.

 

[Janicholson]

Great points. Jim

 

[redforlife]

Cut outs have to have the 4 position light switch. And that switch has to be grounded by way of mounted to box lid, that is bolted to box, that is bolted to steering post. Gots to have good ground through all of that, to the switch.
I doubt you have a 3 position switch, since it worked before. Those are for lights only, and generator is controlled by a voltage regulator instead of a cut out.
My H, I'm not sure charges on the low charge setting. But I know it won't charge on the high setting unless engine is atleast 1/2 or more throttle. Not sure if it is suppose to be like that, or if I just got a weak system which I probly do.
I assume you know how to polarize? It'll charge the opposite way if it needs to be polarized.

 

[pete 23]

I used to run a wire from light switch to generator frame to eliminate all those poor grounding issues of switch to cover to post to transmission cover.

I got tired of polishing up those covers on the light switch etc.

 

[MarkinOhio]

Thanks to everyone that replied to my post. Thanks to your help I now have a functioning charging system. The problem turned out to be the nice shiny paint job the overhaul shop did. A little bit of sandpaper to knock some of that paint off of the 3 mounting flanges got it going. I do think that Im going to use the suggestion from Pete 23 and run a ground wire directly from the light switch to one of the generator mounting bolts. Maybe itll keep charging for the next 72 years that way.