Generator testing

[capecodcub]

Hello all, I have searched the internet and this site, can't find answers I am looking for. I had to rebuild my generator due to bearing issues. I want to test the generator on my bench without mounting to generator. I did do a test that I found where I ground the frame, connect A and F together and apply 6volts. Should run like a motor. I do that and nothing happens. Questioning the internal wiring of the generator. I want to diagnose what is wrong. But can not find any information. Any help would be greatly appreciated. Thanks

[Landreo]

Start with current to the frame and the "A" terminal. leave the "F" terminal unconnected.

Not all generators will run as a motor. I have several in my barn right now that will not motor but will charge fine. The indexing of the brushes for a generator and a motor are in opposite directions. My experience is that the 3 brush generators will not motor well.

Delco recomends on their old adjustable 2 brush generators that the brush index be set so the generator just barely starts to rotate then a partial brush width beyond.

If it runs as a generator it will likely charge but if does not run as a generator it may still charge.

[capecodcub]

I installed the generator today. Polarized(per factory instructions), started engine, no charge. Than, it went full discharge! I had to remove the wire from the A terminal on generator. The belt was also squealing when this was happening. It appeared the generator was trying to turn in opposite direction. I disconnected the field wire as well, powered the F terminal, jumped to the A and it tried to "motor" in CCW rotation. I read on here a man that had same thing. He swapped the F and A wires inside the generator where they connect to brushes and fixed his issue. I did this and it initially discharged but then went to charge! Thought I had it, but then went to discharge again, than full discharge. Tried motoring it again, same CCW direction. What the heck is going on? I have tried finding an internal schematic for the generator with no luck. Just want to get this thing fixed and put back together. Any help would really be appreciated. Thanks

[Landreo]

What is the number on the generator? You did not say what type of generator you have, 2 or 3 brush. If it is a 3 brush, don't remove the "A" wire while running, the field current may climb quickly to field coil burning levels.

If the external wiring is correct, no shorts, and the cutout or regulator are correct then I would remove the generator one more time. You can remove the sheet metal brush cover and lift the 2 or 3 brushes and place a piece of paper under the brushes to insulate from the commutator. Then check the resistance from the "A" terminal to frame and from the "F" terminal to the frame. Should be infinity in both cases. I expect you have a short at the "A" terminal or the brush for the "A" terminal. The insulator that separates the terminals from the case may be damaged or turned such that the internal wire is intermittently touching the case.

Although I think it is of limited value, if you want to motor then do it by connecting negative to the "A" terminal and positive to the frame. Forget the "F" terminal for now. Connecting to the "F" terminal will polarize the generator backwards. I tried 3 more cub generators today and the only one that would motor was the larger 35 amp 2 brush. Neither of the 3 brush generators would motor at 6 volts.

Make sure you are polarizing correctly, polarizing backwards will cause nothing followed by a large discharge as the cutout points weld themselves into one mass. Polarize by connecting a jumper wire from the battery terminal on the cutout/regulator to the "A" terminal just long enough to make a spark. The "A" terminal should be made NEGATIVE for that brief moment assuming you have a 6 volt positive ground system.

Take the cover off the cutout or regulator, that large discharge may have welded the points together. Check for free movement.

If the test for shorts is negative then I would look at the wiring as best you can without removing the end of the generator. One brush goes to the frame/ground. The other brush has 2 wires, the field wire, and the "A" terminal wire for 2 brush generators. For 3 brush, one brush to the ground, 180 degrees opposite, roughly, is the "A" wire, the off angle 3rd brush should have the thinner field wire. If all looks good or you cannot see the wires good enough then I would just pull the end off and inspect.

[capecodcub]

Landreo, that information is exactly what I have been looking for! Thank you very much. Too cold right now, but will be out in barn in the morning and going thru those tests and will report back. After some other testing earlier, I did motor it correctly, but when disconnecting the ground from the F terminal, the gen just stopped. And, when I was connecting the wire to A, it really sparked like a dead short. Assuming I have something touching somewhere and need to diagnose and find that. More to come.....

[Landreo]

Some information on old delco generators:

http://www.easy39th.com/files/TM_9-1825A_Electrical_Equipment_(Delco-Remy)_1944.pdf