Originally posted by big_mack:
Good logic, except a circuit with a motor in it is not purely resistive. If there is enough voltage present the motor will try to start, start-up causes a current spike which stresses components (like the relay) or blows a fuse. If the connection is bad enough, the motor will do nothing even though there is nothing wrong with the motor itself.
It's not logic, it's physics.
Any current spike will be limited by any in-circuit resistance.
If a faulty (high resistance) connection is present, the motor cannot draw current adequate. Any inductive reactance would, in this instance, likely be coincidental. In any event, the reactance would add to the load making the total load greater which, according to Ohm's Law, will decrease total current in the circuit.
If the motor is drawing excessive current at startup, it most likely is defective due to seized bearings or a faulty connection between the brushes and the commutator shaft. Shorted windings are another possibility.
Steve
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