Why are potentiometers not a good method of speed control

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Discussion Overview

The discussion focuses on the limitations of using potentiometers for speed control in electric motors, particularly in terms of energy efficiency and performance. Participants explore various aspects including energy losses, regulation quality, and practical challenges in implementation.

Discussion Character

  • Technical explanation, Debate/contested, Conceptual clarification

Main Points Raised

  • Some participants argue that using potentiometers leads to significant energy losses, which decreases the efficiency of the motor.
  • One participant highlights that reducing voltage with a potentiometer increases current for the same horsepower, resulting in higher I²R losses.
  • Another point raised is that speed regulation using potentiometers is poor, which affects overall performance.
  • Participants note the difficulty and expense in finding potentiometers with significant power handling capability.
  • A participant mentions that while Scalextric speed controllers are an example of potentiometer use, their poor regulation is acceptable in that context due to the nature of the application.
  • Historical context is provided with reference to large electric locomotives that used series resistors for speed control, suggesting a different method of implementation compared to potentiometers.

Areas of Agreement / Disagreement

Participants generally agree on the inefficiencies and challenges associated with using potentiometers for speed control, but there are varying opinions on specific applications and alternatives.

Contextual Notes

Limitations include the dependence on specific motor characteristics, the context of use, and the potential for varying performance based on application requirements.

rehaan
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Why are potentiometers not a good method of speed control(in terms of energy)?
 
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there will be huge loss in terms of energy thereby decreasing the efficiency of the motor. for example consider 200V, 1HP motor. if you decrease the voltage by potentiometer current will increase for same HP...which increased I^2R loss...you cannot increase the voltage beyond rating because this will cause insulation problem and flux weakening...
 
Aside from the obvious wasted power, speed regulation is poor.
 
and also finding ones that have any significant power handling capibility is difficult and expensive
 
davenn said:
and also finding ones that have any significant power handling capibility is difficult and expensive
Scalextric speed controllers are a cheap and cheerful example but, because of the short lap times involved, the bad regulation doesn't matter and the player can compensate with skill.
Speed control of large electric locomotives used to be achieved partly with series resistors. Those resistors were fearsome looking but I think the resistances were switched with a large brass wiper and brass contacts, rather than constantly variable.
 
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