Generator help.

[JohnDeereM50]

Still trying to get rebuilt generator on my M to charge. Brand new everything and I mean absolutely everything. Bright shiny metal at all connections with internal and external tooth washers to boot. Still doesn't charge one single bit.

On the other hand just got done restoring a 57 420 for a man. Instead of getting old genny redone we got a remaned unit online that was rebuilt only God knows where. As soon as I fired it up and gave a little throttle it charged great.


I tried all the tests. Take belt off, ground field, apply power to armature. Genny will spin. Remove ground on field and it should speed up, it doesn't it stops spinning. The place that rebuilt it says this doesn't matter but I think it does. Grounded field while running no charge. Jumped across cutout relay while running no charge. Amp meter works and shows discharge while lights are on. What am I missing I'm pulling my hair out over here.

 

[rick deere]

generators are positive ground

 

[WGM]

Generators can be either positive or negative grounds.

 

[semper_deere]

If the generator stops then there is an open in the coils (I would guess the armature somewhere a growler test should find it). Removing the ground should lesson the magnetic flux of the field magnet and the system would continue to spin with residual magnetism and the external application of current making up for friction losses. With the flux reduction of the field there is less drag on the armature and the speed will increase. So yes this part of the test is important.

 

[David G]

Did you polarize it?

 

[John T]

That "stops spinning" part when the Field is ungrounded makes me think its a bad genny regardless what you were told. And when you did the field ground and cutout relay by pass all else was out of the circuit so if it still didnt charge that leaves the genny as the culprit BUT THAT ASSUMES ALL ELSE IS IN PLACE AND WIRED CORRECTLY !!!

Just have to ask, you did Polarize the genny right??? Your tractor is at POS ground while the genny may well have been polarized for NEG ground when it was rebuilt.

Id use an ohm meter on the low Rx 1 scale to ohm out the field coils for continuity and expect the two to be in series (they splice there in the middle) and read in the vicinity of maybe 3 to 8 ohms and the field coils cant be shorted to case ground ya know. Likewise NONE of the armature windings can be shorted to the shaft. If its removed and you put an ohm meter lead on the shaft then run the other lead across the commutator segments, NONE should read continuity/short to the shaft. Really need a growler to test the armature but the above still holds true NO SHORTS

Is yours a 3 brush genny??? if so the field circuit begins at that third brush and splices then to the other field then ends up at the FLD post. You may wanna check out all that circuit for continuity and no frame case ground shorts.

I just suspect the genny if all else is in place and wired correct and you correctly ran the by pass and field ground checks.

Let us know what you find.....

John T

 

[John T]

Rick, it will chare at POS or NEG Ground and it initially begins charging (on residual magnetism in the field poles) at the polarity at which it was polarized.......

John T

 

[teddy52food]

If every thing else checks out, there is one thing that can't be tested for and that is a flying short in the armature. That is when a wire is loose and contacts ground while running and not otherwise. You may need another armature, but that field test doesn't sound right.

 

[johnseerem50]

Yep polarizing it was the first thing I did after bolting it to tractor and making all connections before starting.
Before I tear into it myself I spoke with the place that worked on it, they want me to return it to be looked at. So I guess I'll let them do that.
Over 500 dollars worth of electrical parts on the tractor. No stone was left unturned, I've placed everything, something's more than once.