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Test Procedure for Aircraft Motor/Generator

To check that the motor is operational, connect the negative terminal of a 12 volt battery to the "E" armature terminal of the motor.

Tap the "A" (field) terminal of the motor to the positive of the battery with a connecting wire. TOUCH the Terminal only to avoid damage to the threads. If you obtain a "soft" inductive arc, you may assume you have an unbroken field winding that is working correctly.

Holding the connection to the "A" terminal for more than a 1/2 second can produce a long arc. A sharp arc with a shower of sparks means you have the wrong terninal or a shorted field winding. Do not hold on to the connecting wire and the "A" terminal at the same time to avoid getting a high voltage shock. Normal field resistance is 2.2 ohms. If you have a sharp high current snap, you probably have the "D" terminal.

The "D" terminal is NOT USED when the device is used as a motor. It is used when employed as a generator on multi-engine aircraft to balance the loads.

The field is NOT connected directly between the small "A" and "D" terminals. The field is connected between the small "A" and the large "E" terminals. The armature is connected between the large "B" and "E" terminals.

Connect the positive terminal of the battery to the "A" motor field terminal. With the motor held down, connect the positive ("A") to the "B" terminal.

The motor should now turn at about 1000 RPMs. The idling motor will probably draw between 20 and 30 amps from a charged 12 volt battery. The motor will turn in a counter-clockwise direction as viewed from the shaft end.

If the motor turns in the opposite direction or draws significantly more current with a tendency to rotate at a higher speed then the field is either not connected or is bad. A dirty commutator or bad bearings will also cause the current draw to be higher than normal.

For "bench testing", operating unloaded for testing and operating for seating brushes, forced air cooling is not needed. Proper shop safety precautions should be exercised when testing any electrical device. Eye protection, gloves and no loose fitting clothing just to name some. DO NOT connect anything to the motor shaft as the motor developes very high torques. These motors can provide in excess of 1 foot pound of torque per amp of draw - a locked rotor can draw up to 900 amps! Be sure your motor is securely held down for all testing.

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