Generator - motoring to test

malpais

malpais

Well-known member
I've read on this forum a generator can be motored to test it. I found two '40ish generators in a u-pull-it lot last week. Took them apart, cleaned out the mud and corrosion, freed up the brushes, and hooked them up to "motor" and both do motor. In this test, how fast should they turn and should they have much torque? I'm thinking the brushes probably are not fully seated, and there's still a little cleaning to do, but they don't spin fast or with great torque. Just wondering if they are "spares" with a little more work, or merely cores.

Thanks,

Gordon
 
Just a basic test to see if they will generate.Not fool proof or how well it will work.They don't spin fast or generate much torque,but a good chance that it will work. Phil
 
50 some years ago, I worked for my neighbor's auto electric shop and one of the jobs was rebuilding generators. We had a test stand that must have had a 5 HP motor in it. We'd spin the generator with a coupling with a 15/16 socket on the pulley nut. We'd connect the output thru the field coils. It put a real load on the generator and we got monstrous sparks when we pulled the jumper off the fields. Main thing we looked for was arcing at the brushes under load.
 
I just went through this with the generator on my 36. It turned very slowly with no torque when hooked to a battery on the bench. Turned out I had a bad amature as confirmed by a test on an Armature Tester (Growler). Rebuilt it with a new armature and it turned 3 times as fast and more torque than you would want to try and stop with your bare hand. Hope this helps.
 
Thanks all for the info and ideas.

Guess these generators aren't totally bad, but maybe armatures aren't great. I thought armatures were either good or bad - but I guess certain coils can be bad. You guys evidently had more speed and torque than I'm seeing.

Since I don't have a growler, I may just stick the generators on my engine in the 39 frame, fire it up and see what happens.

Pete, I was thinking about what kind of motor would be needed for a test stand -sounds like you used a big one. I may build a little jig and hook them to my 3 hp table saw motor.

All info is appreciated!

Gordon
 
I should have mentioned that the test stand we used had a variable speed device. I don't know if an induction motor like that used on a table saw would like running on a heavy load at lower speeds. If you had some sort of series wound motor, that would be better. Actually, a series motor could be run on AC.
 
Richard - I hadn't thought about repolarizing -bet running one as a motor does turn the fields around. Pete, a test run with an ac motor sounds like too much trouble for me I'll just try 'em on a running engine.

Gordon
 
If you can mount them on your car do so and once you get it running remove one of the battery cables, if car stall the gen is shot , if car stays running gen OK. Pete/Ct
 
Pete/Ct. said:
If you can mount them on your car do so and once you get it running remove one of the battery cables, if car stall the gen is shot , if car stays running gen OK. Pete/Ct
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Don't do this with an alternator, it will kill the alt...
Karl
 
Thanks again. Used to remove the battery leads in the cars and tractors I grew up with to see if generator was working. Was afraid of hurting an alternator or a computer on later ones.

I can check voltage and maybe amperage once I stick 'em on the engine. Just have half a dozen or so to check. Charlie in NY has been helping me on which one or type to use on a 39 pu with 53 engine.

I want to get rid of some when that's determined. Amazing how a 30' x 40' barn can fill up with Ford junk

Gordon
 
I have an old cub cadet lawn tractor, the generator doubles as a starter. The wiring reverses the power to the generator to crank. Harley
 
Starter generators usually have a different (seperate) set of coils for the field. Real heavy ones for motoring and real fine wire coils for generating. If you motor a generator too much, you can damage the armature coils from the heat that is generated. Finer windings make more heat faster.

A fellow I worked for when I was a kid used to alligator clip a test lamp up to the generator terminals and turn the armature pulley by rubbing it into a moving buffer wheel on his bench grinder. If the light started to glow, he knew it would at least generate something of a current. As was previously mentioned, if you motor one, depending on which way you connect it, you can change the polarity of the field shoes. Definitely re-polarize it before running any tests on it. On most motors you can change the direction of rotation depending on the polarity of the hook up but some brushes are set to only go one direction and can be ruined if they turn the wrong way.
 
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