Generator - Motor test.

[banjoman09]

Farmall H - 6 V- when I take the belt off- run a jumper to Arm on generator it does motor- then with Field grounded - unhook the jumper wire from Field- it runs a bit faster....is this right? Still not sure why it will "motor" if Arm post is not "hot" when tractor is running- must be a bad Genny?

 

[John T]

Often if it passes BOTH motor tests it will charge but that's NOT always true. Motoring with voltage across ARM and ground makes it spin like the DC motor it actually is and that often means the brushes and armature and bushings are at least in decent shape. With the fields in the circuit a back emf is created slowing it some but when removed and it spins faster that shows they were conducting current SO PASSING BOTH TESTS OFTEN MEANS THEY SHOULD CHARGE IF ALL THE REST AND WIRING IS OKAY............

MY Charging Troubleshooting may help.

John T
John Ts Troubleshooting

 

[banjoman09]

Yes- we talked last week; passes both tests- so why is the Arm post on Genny "not hot" while running? I still need to replace the 14g wire with 10g- but Arm post should still be hot.

 

[John T]

If theres no voltage between ground and ARM on genny when running and especially if FLD is dead grounded the genny must be bad even if it passes motor test.......

John T

 

[teddy52food]

Flying short to ground in the armature.

 

[banjoman09]

hmmmm.....ok...

 

[55 50 Ron]

A little more explanation please.

 

[Janicholson]

If you actually fix the small (possibly damaged) wires from the Arm terminal on the gen to the Arm terminal on the regulator, and the wire from the Bat terminal to the ammeter. These must be replaced. please be assured that if you read any voltages before these are replaced you are mistaking resistance for differing problems, and it is not safe. You have stated voltages of 8 plus on terminals with it running. You have also stated that it charges when the field is grounded directly. It cannot charge if the arm terminal shows no voltage. These contradictory readings might be related to the small wires used in the output. Replace those wires please. Jim

 

[John T]

Also any open unloaded voltage from ARM to ground doesn't tell the whole story as its the voltage once connected to a load that really matters and once connected it should be capable of raising the voltage of the battery........ BUT no voltage from ARM to ground sounds weird as even a half good genny should produce something especially unloaded due to residual magnetism in the soft iron field poles even with bad fields.

John T

 

[Rich'sToys]

Following these two threads has been kind of like watching a soap opera! :roll:

 

[banjoman09]

Sorry!

 

[banjoman09]

Will try to get this done today....thank you.

 

[teddy52food]

Break down of the insulation on a wire in the armature. When it spins up to speed , the centrifugal force moves it enough to touch & short to ground. It will still motor ok as the speed is to slow to move it.

 

[buickanddeere]

I don't use a jumper wire. Instead hold the cutout contacts closed, then if it motors . Open the field contacts and the Rome should increase .

 

[banjoman09]

Well- it could be breaking down when it runs; I took the Genny apart- again- no short on armature- ohms out ok- the wires are bare in a few spots going to brushe4s; the third brush I do NOT see where you can "adjust it"...just has a screw like the other two. I better look for another generator. Thanks!

 

[banjoman09]

when it "motors"...it is not very fast.

 

[erskine2017]

You don't check an armature for shorts with an ohm meter. You must use a growler. Even the there is the possibility of a "flying short" as described below. An ohm meter is a lazy way to check field for shorts or grounds. A better way for fields is to hook a battery and amp meter in series with the fields and measure current draw. This method heats the fields in real conditions which an ohmmeter can't do. An ohmmeter will tell if the fields are bad but not if they are good.

 

[John M]

The screw is on the back of the case.

 

[pete 23]

Put an ohmmeter on each brush to commutator to see if you get a near zero reading on the meter. High mica like I said before will interfere with a good connection AND, a lot of rebuilders use a brush that is way too hard for a generator. You want a brush that is soft. I usually seat brushs by wrapping commuter with sand paper, about 150 grit or so, then install end plate on armature and a good generator brush will let a lot of material wipe onto paper. Hard brush , like used in starters will take pressure applied more than just the spring pressure. Just another reason I hated rebuilt generators. We used to have a special roll of commutator sand paper but suppliers discontinued that. I also measure field current flow with an ammeter along with the growler test on armature to check for shorted winding in armature.

 

[banjoman09]

okay- well we can "scrap" this post! I took it off the tractor to check it out again- I rebuilt it 6 months ago and it did work fine- then quit. While I was taking the brushes off to separate the wires I broke a brush holder...then got mad and thru it on the floor. I am now looking for another good one that works. Thanks to all who have tried to help me! Banjoman

 

[banjoman09]

that's all I have .....