Current measurement of a PM DC generator

AI Thread Summary
A small PM DC motor is being used as a generator to convert mechanical energy into electrical energy, with current measurements taken while driven by a DC motor. Initial current readings align with theoretical predictions but gradually decrease over time, despite constant motor speed. Possible reasons for the current drop include overheating of the generator, a shorted turn, a commutator fault, or issues with the external resistor or measuring equipment. The discussion raises concerns about the generator's functionality and the accuracy of the measurements. Understanding these factors is crucial for diagnosing the generator's performance issues.
GraysonSH
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Hi,

I'm trying to use a small PM DC motor as a generator to convert mechanical energy to electrical energy.

I couple that small generator to another DC motor with spur gears and I measure the current of that small generator while it is driven by the DC motor at fixed speed. The circuit of the DC generator is closed by means of connecting an external resistor in series to the generator terminals.

The initial current reading is, say 0.1A, which is approximately same with theoretical prediction. However, the current reading drops gradually as time progresses and eventually settles down at, say 0.02 A. The speed of the motor remains unchanged.

Why does the current reading of the generator drop while the rotation speed remains unchanged? Does that imply something is wrong with the generator?

Thank you.

SH
 
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Welcome to PF.
Is the generator getting hotter as the current falls?
It may have a shorted turn or a commutator fault.
Does your resistor stay the same value? It might be a PTC thermistor!
Is your meter working correctly?
 
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