MTFCA Forum

My generator was working just fine a few days ago and then it wasn't. I could see one brush screw had fallen out leaving the brush and coil wires flopping around.

Gaining access to that brush required removing the generator — a closer look revealed dodgy insulation on the coil wires and failing brush plate insulators.

I replaced the brush plate insulator strips with the new fibreglass(?) ones, re-insulated the field coil wires, and replaced the terminal wire. So far, so good.

I then locked the brush plate in the neutral position (12vt+ to the output terminal, —ve to the case, 3rd brush lifted) where it would not motor in either direction (actually it really only motored in one direction and barely tried to motor at the other end of brush plate travel). After dropping the 3rd brush onto the armature, the generator motored nicely on 6-volts and drew about 4-5 amps. Again: so far, so good.

Reinstalled the generator on the engine, fired up the engine and... nothing. Zero output showing on the ammeter throughout the full travel of the 3rd brush. So far, so bad.

I experimentally bypassed the Fun Projects regulator with a jumper wire but once again, zero output. I connected a 6-volt bulb between the generator terminal and the frame but again, nothing.

Although the MTFCA Electrical System book has been generally helpful, from what I've read this darn thing should be working just fine.

I'm at a loss as to where to go from here. Could the problem possibly relate to the neutral setting in that I couldn't achieve active motoring at each end of the brush plate travel? If not that then what? Inquiring mind wants to know...

Maybe it's just your photo, but I don't think I'm seeing an insulator between your 3rd brush and brush collar. Is that possible?

Hi Chris,
I had a similar experience the other day. I was adjusting the output on my spare generator on a test stand and rotated the entire brush plate slightly (4 screws). After doing so, I had no output. If I pressed the 3rd brush against the commutator while it was running, it would show an output. I lightly sanded the 3rd brush using a method from the MTFCA electrical book, and right away it worked again. The 3rd brush is used to power the field coils, so it needs to be making good contact. When I moved the Brush plate it must have changed the angle of the brush such that there wasn't as much surface contacting, and sanding the brush made conform again to the commutator.
Hope this helps, Bill Coyle

Thanks Jerry and Bill for your replies...

There is indeed a new insulator on the brush plate although it’s hard to tell in the photo.

Bill, I owe you a coffee or a beer or whatever beverage you prefer — that’s exactly what it was. Much appreciated!

Chris,
You're very welcome, glad to hear of your success!
That's thanks enough for me!
Bill