Current measurement of a PM DC generator

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SUMMARY

The discussion focuses on the performance of a small Permanent Magnet (PM) DC generator when coupled with a DC motor. Initial current readings of 0.1A align with theoretical predictions, but readings drop to 0.02A over time despite constant motor speed. Potential causes for this decline include overheating of the generator, shorted turns, commutator faults, or issues with the external resistor, which may be a PTC thermistor. The accuracy of the measuring meter is also questioned as a possible factor.

PREREQUISITES
  • Understanding of PM DC motor and generator principles
  • Basic knowledge of electrical circuits and current measurement
  • Familiarity with thermistors and their behavior in circuits
  • Experience with troubleshooting electrical components
NEXT STEPS
  • Investigate the effects of overheating on PM DC generators
  • Learn about diagnosing shorted turns in electric motors
  • Research commutator faults and their impact on generator performance
  • Examine the characteristics and applications of PTC thermistors in circuits
USEFUL FOR

Electrical engineers, hobbyists working with DC motors and generators, and anyone involved in troubleshooting electrical systems will benefit from this discussion.

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
 
Engineering news on Phys.org
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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