Current measurement of a PM DC generator

In summary, the conversation discusses using a small PM DC motor as a generator to convert mechanical energy to electrical energy. The current of the generator is measured while it is driven by a DC motor at a fixed speed, with an external resistor connected in series. The initial current reading is close to the theoretical prediction, but it gradually drops and settles at a lower value, despite the motor speed remaining the same. Possible explanations for this phenomenon are discussed, including the generator getting hotter, a shorted turn or commutator fault, a PTC thermistor in the resistor, or a faulty meter.
  • #1
GraysonSH
1
0
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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  • #2
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?
 

1. How is current measured in a PM DC generator?

The current in a PM DC generator can be measured using a device called an ammeter. The ammeter is connected in series with the generator's circuit to measure the flow of current through the circuit. The ammeter must have a low resistance to avoid affecting the circuit's current flow.

2. What is the purpose of measuring current in a PM DC generator?

The measurement of current is important in a PM DC generator as it allows us to monitor the amount of electricity being produced by the generator. This information can be used to determine the efficiency and performance of the generator, as well as to troubleshoot any potential issues.

3. How does the current measurement affect the operation of a PM DC generator?

The current measurement does not directly affect the operation of a PM DC generator. However, it provides important information that can be used to optimize the generator's performance and ensure its proper functioning. It also helps in identifying any potential problems with the generator's components.

4. Can the current measurement be affected by external factors?

Yes, the current measurement in a PM DC generator can be affected by external factors such as temperature, humidity, and the presence of other magnetic fields. These factors can alter the resistance of the circuit and affect the flow of current, resulting in inaccurate measurements.

5. How can the current measurement be improved in a PM DC generator?

To improve the accuracy of current measurement in a PM DC generator, it is important to use a high-quality ammeter with a low resistance. The generator's circuit should also be properly insulated to avoid any external factors from affecting the measurement. Regular maintenance and calibration of the measuring equipment can also help in improving the accuracy of current measurement.

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