generator motor test

[Anonymous-0]

Question for John T

Worked down your generator trouble shooting list to # 6. THE Motor test (first time I got that far with out a solution) When I applied the power to generator the electric magnet locked up the motor I.e. pulley would not turn. I remove electric line and pulley would turn again. Is this an expected out come or did I hook it up wrong?

 

[John T]

If you ground the frame/case,,,,,,,attach/jump the Field post to frame/case/ground,,,,,and apply hot voltage to the ARM post ID EXPECT IT TO SPIN like the DC Motor that it is. If not, I suspect a bad armature or worn brushes. Maybe the armature is grounded (shorted windings) or maybe the bushings are worn and its dragging the Field poles or maybe the commutator is burned. If they are okay then Id wonder if the brushes are making contact with the commutator??

That lock up situation sounds more like an armature problem from sitting here. If it were removed NONE of the commutator segments should have continuity to the shaft cuz that means a shorted winding and there should be continuity from one segment to the next one throughout.

Dig a lil deeper I reckon

John T

 

[Bob]

Also, if a bearing(s) or bushing(s) is bad, and the armature contacts the field polepieces, it will lock up when power is applied, and the polepieces get magnetized.

 

[John T]

Good point Bob, another thing I thought about is if the armature had a complete open winding between two commutator segments (or a total bad segment) it might just turn to that one spot n quit cuz theres no more rotational magnetic field to keep it turning past there????

Regardless if armature or commutator or very bad bushings sounds like his genny needs some serious attention

John T

 

[Lee B]

You did not hook it up wrong and it IS an expected outcome in the scenario that Bob describes. In other words, at a minimum, you have at least one bad bearing or bushing in that generator and it must be replaced. When under the Motor test, the poles are stongly magnetized which attracts the armature to them and if they can touch because of excessive bearing clearances, they do and it always locks up at that point. This is the whole point of performing the Motor test and the test has shown that your generator needs some bearing work just for starters.

This contact from excessive clearance also comes into play when the generator is operating normally where the momentary contacts lead to a lot of friction and heat building up which then quickly leads to blue laminations, a shorted armature and eventually a whole new generator. So now because of the risk of that situation, you really should remove the armature to be tested for shorted windings on a growler.

A growler is an old-time transformer type machine that can find shorted sections of an armature. If any one section is shorted then the whole darn thing needs to be rewound or replaced at that point. Only a growler can find this common defect in armatures also.

I hate to be the bearer of bad tidings but I've never seen a generator with a rubbing armature that WASN'T shorted internally and basically scrap metal. Rewinders don't even want them when they have rubbed too much.

 

[John T]

Lee, I never owned a growler but one can still find bad shorted armatures without one simply by using an ohm meter (or even battery/light type continuity tester if the "shorts" not highly resistive) cuz if any commutator segments register continuity to the shaft IT MEANS THE WINDING IS SHORTED. Attach one end of the meter/tester to the shaft then use the probe to contact the segments and HOPE THERES NO CONTINUITY LOL When shorts are bad enough one can find those badly burned n pitted commutator segments and/or armature winding burns n that color stuff you mentioned.

Fun discussion

John T

 

[Lee B]

Hi, John. You are only partially correct and that's only when you gots the right kind of armature short. In my case, the kind of short that one can find with a $10 multimeter (your example) never happens and instead, the windings short only to themselves - and THIS kind of short, ONLY a growler can find. To restate things, the growler will find both kinds of shorts and the multimeter can only find the rare type of short. And that means... ONLY a growler test can give a 100% good to go status to an armature.

The multimeter findable short happens a short time after one keeps on using a generator with the growler "only" findable short - believe that part if nothing else, they do NOT fix themselves and can only go from bad to worse and in a jiffy. The real trouble here is that once you have a generator that is dragging you have only a minute of running time to stop using the generator or you'll cook it past the point of being usable ever again. AND if it has ANY shorted windings no matter if it's the multimeter type or the growler "only" type, of course it's just plain done for.

My Uncle gave me his old growler a few summers back figuring I had more use for it than he did. At the time, I had an armature to test and knew he had one, so we dug it out from under a bunch of junk and set about to give it whirl in the back yard. It turns out that this one was a "complete" tester in that it also could test for open windings in that it had a 110 volt, 100 watt light bulb with two probes ready to go. When you touched the probes together, the light bulb would light up, nice and bright. This sure would find that winding that was shorted to the shaft!! Just don't be touching anything metal when you do... And stay away from any mud or water or... Talk about being nervous.

Old dirty wooden handled probes just screamed "I'll shock you" at me, the rotten and falling off wire insulation was no treat to look at either. I'm thinking this part of my new growler will be electrically disconnected and not used any further... I can use the $10 multimeter for these tests which DO need to be done as well as the basic growler test for shorted windings. My armature passed the test BTW, with no causalities either, thankfully.

One oldtimer generator tip I can pass on to others is to look for ring of slung solder inside the generator case at the brush end. When an armature gets too hot, the solder connecting the windings to the copper commutator strips melts and gets thrown out against the case in a very noticable ring of little solder beads. Being very easy to overlook, one often only "sees" it when he is reminded to look for it, but once you've found it you can pretty much just count on buying a new generator at that point. Any further diagnosis is a total waste of time. It's kind of like finding those blue laminations of an armature I mentioned before - they are not a good symptom to see either.

 

[P Browning]

Lee -- Thanks for taking the time to prepare that piece -- quite enlightening! (PatB)