The Ford Barn

Tom Wesenberg · 11-24-2014, 12:45 AM

I just recieved a question about a generator that won't motor, and was asked what to check. First be sure you are using a car battery or at least a 6 amp battery charger when trying to make it motor. If it motors, that's a good first sign, but not proof positive that it will generate electricity. If it won't motor, that is proof positive that it needs to be worked on.

Start with a visual check to be sure you don't have a broken wire or worn out brushes. Make sure the field wire goes to the adjustable brush.

You can lift the adjustabe brush off the commutator and slip a piece of paper under it to isolate the field windings. (If the generator is apart, of course you can skip this step). Then connect a battery charger + to the case and - to the wire on the adjustable brush. A good field winding should draw about 4 to 5 amps. If this checks OK, then use a growler to check the armature. If the armature has thrown solder, you may get lucky and be able to resolder the wires at the commutator bar, or they may still have enough solder to work OK.

Check for continuity between the commutator and armature shaft. There should be NONE. Do the same for the field winding, but you will have to remove the ground end of the field winding to make this check.

Sometimes the twisted connection between the two field coils isn't a good soldered joint.

Make sure the commutator bars are smooth, not burned, and undercut at least .006" with no grit, carbon or copper in the undercut. Make sure the brushes ride square to the commutator, not cocked in the holder, or with a bent holder.

The long side of each of the 3 brushes is mounted AWAY from the pivot point of the brush holder, and the thin brush is the adjustable brush.

Make sure you don't mistake the 2 wires that connect to the brushes. I've seen generators burned up because some shop put the field wire on the output brush, instead of the adjustable brush.

If the visual checks out, and the field windings check good, then it's likely the armature is bad and will need to be checked on a growler.

11-24-2014, 12:45 AM	#1
Tom Wesenberg Senior Member Join Date: May 2010 Location: Mpls, MN Posts: 27,582	Generator Won't Motor---Now What to Check I just recieved a question about a generator that won't motor, and was asked what to check. First be sure you are using a car battery or at least a 6 amp battery charger when trying to make it motor. If it motors, that's a good first sign, but not proof positive that it will generate electricity. If it won't motor, that is proof positive that it needs to be worked on. Start with a visual check to be sure you don't have a broken wire or worn out brushes. Make sure the field wire goes to the adjustable brush. You can lift the adjustabe brush off the commutator and slip a piece of paper under it to isolate the field windings. (If the generator is apart, of course you can skip this step). Then connect a battery charger + to the case and - to the wire on the adjustable brush. A good field winding should draw about 4 to 5 amps. If this checks OK, then use a growler to check the armature. If the armature has thrown solder, you may get lucky and be able to resolder the wires at the commutator bar, or they may still have enough solder to work OK. Check for continuity between the commutator and armature shaft. There should be NONE. Do the same for the field winding, but you will have to remove the ground end of the field winding to make this check. Sometimes the twisted connection between the two field coils isn't a good soldered joint. Make sure the commutator bars are smooth, not burned, and undercut at least .006" with no grit, carbon or copper in the undercut. Make sure the brushes ride square to the commutator, not cocked in the holder, or with a bent holder. The long side of each of the 3 brushes is mounted AWAY from the pivot point of the brush holder, and the thin brush is the adjustable brush. Make sure you don't mistake the 2 wires that connect to the brushes. I've seen generators burned up because some shop put the field wire on the output brush, instead of the adjustable brush. If the visual checks out, and the field windings check good, then it's likely the armature is bad and will need to be checked on a growler.