The Stovebolt Site Forums The Shop Area The Electrical Bay 12v Generator Armature - continuity to ground (?)

I think that I screwed up my generator. Can you give me some direction?

>> Should the Armature stud have continutiy to the generator case (ground)

Background --

12v generator of unknown heritage in my '54 3104. No markings on the case.

I removed the hex nuts that secure the F and A studs to the generator case to replace with new nuts and to add an insulator and "Radio By Pass Condenser" tag to the Field stud. The threads on both studs are boogered so I probably rotated them a few degrees in the process.

I drove the truck about 15 minutes before I noticed that the ammeter showed that the gen was not charging.

I pulled the generator, removed the commutator end frame, and saw that I had broken the Field wire to the Field stud. Plus, my ohmmeter shows continuity between the Armature stud and the generator case (ground.)

Could the short between the Armature and the case have been caused by driving with the broken Field wire? Or is it normal? To my untrained eye, nothing looks unusual under the Armature stud.

< Pic of broken Field wire and partial view of Armature stud >

Should be pretty easy to replace both boogered studs and to reconnect the Field wire if nothing else is wrong.

Thanks for your help (again),

WOO HOO -

Ken at ClassicGenerator.com told me that the Armature continuity is OK because the brushes are in contact with the Armature. All I need to do is resolder the Field wire to the Field terminal.

Dodged another bullet!

Ken sold me the ByPass Condenser tag, new insulators, and hardware that I am using - plus he has answered a ton of stupid questions. FYI - the tag has a #12 hole in the center instead of the big hole that the parts houses sell. It fits onto the generator Field stud like it should. Thanks, Ken.
< ClassicGenerator tag >

Unless you insulate the brushes from the armature commutator, the ohmmeter will indicate a short. There should not be a circuit from the commutator to the armature core, but one of the brushes is grounded. The other brush is connected to the ARM terminal and the circuit tester will show a clear path to ground even on a good generator. That's why it's necessary to have a cutout relay on a DC generator system. Fix the broken wire, and you should be good to go!
Jerry

If you want to do a further check, slide a piece of paper between one of the brushes and the commutator. You should show an open circuit then on armature to ground.