I have a 2 field a\c electric motor that quit working. When I check at the brushes I have power but only way I can get the motor to run is take a wire from ground and rub the armatur. Any ideas on what is wrong?

Russs

Is this an AC commutator motor?

If you are unsure, please provide manufacturer and nameplate information. You can also identify it as a machine that has slip rings and a commutator, and that the commutator brush rigging moves to vary speed at constant torque.

Howard

It is a .75 2 gallon Mity Mite air compressor
120 volt
10 amp
60 hz
.75hp

Ah, an unusual question for this forum.

If you need to use the ground wire against the rotor in a small single phase motor then you have one of the following problems:

1. A bad neutral wire (least likely);
2. A sticking start switch, if you have a mechanical switch, or open switch if it is electronic. A mechanical starting switch is located on the shaft of the rotor and should move in and out (it is called a centrifugal switch). It will rub against a contact in the motor that engages a start capacitor and the start winding. If the switch does not work, then there will not be enough starting torque.
3.A bad starting capacitor (most likely, if you have been using it for a while). You can test the capacitor using a multimeter set in resistance (ohms). Place the multimeter first with the red and black across the tabs of the capacitor there should be an increase in resistance that continues to climb until the instrument shows infinite. Switch the leads which should cause the reading to decrease then start to increase again.

In either case, you will also want to make sure that the connections are correct, if it is new (you may also wish to return it for warranty).

Sincerely,
Howard

MotorDoc
Thanks I just got around to checking that out and it turned out to be a inline fuse block on the power (black line) feed because of you I checked deeper instead of just tossing it, and it works graet now. You saved me $200.00 dollars. Russ