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Re: Blower Motor Drags Voltmeter Down 300 1986

posted by  someone claiming to be Don Foster on  Fri Sep 14 23:32 CST 2001 [RELATED]

"...possibly the brushes are just about worn out?"

Umm, I don't think this wouldn't cause a voltage drop. A voltage drop is caused by increased resistance in the circuit or increased current flow through the circuit.

Worn brushes inside the motor would increase the motor resistance, which would decrease the current flow through the motor. This would mean the fuse circuit would experience less voltage drop, so the voltmeter would dip less when the fan was used.

A shorted motor would draw more current, and this would cause the voltmeter to drop significantly. I don't think these motors fail that way, however.

The Volvo voltmeter is connected in the fuse block assembly on the "down stream" side of a fuse, along with the various loads such as the blower. Any contact resistance at a fuse (corrosion) results in voltage drop at the point of resistance. This lowers the measured voltage.

This is all Ohm's Law.





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