DC Motor Field Current Speed Control

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Discussion Overview

The discussion focuses on controlling the speed of a Geared DC Motor using a field current control circuit. Participants explore theoretical resistance values for components and the suitability of different circuit designs for achieving variable speeds.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes the specifications of their DC motor and seeks advice on resistor values for a field current control circuit.
  • Another participant asserts that the proposed circuit will not function as intended, suggesting that the resistors would merely act as an additional load on the power supply.
  • A different participant acknowledges the previous point and suggests using a 555 Pulse Width Modulation (PWM) circuit instead, indicating a preference for a simpler solution.
  • Another contribution emphasizes that using a potentiometer for high currents is inefficient and recommends using switches like transistors, noting that the original circuit design is in parallel with the motor, which would prevent speed control.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness of the proposed circuit and the use of resistors versus PWM for speed control. There is no consensus on the best approach to achieve variable speeds.

Contextual Notes

Participants have not reached a conclusion on the appropriate circuit design or component specifications. The discussion includes assumptions about circuit configurations and the behavior of components under load.

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I have a Geared DC Motor rated 12V, 0.6A, 180RPM, 3kg.cm, 66% Efficiency. I measured the impedance of the disconnected motor at 45 Ohm.

I want to use it with a with a simple 12V 1A DC Power Supply in a Field Current Control Circuit to be able to dial in variable speeds.

Will the circuit in the attached diagram work?

What are good Theoretical Resistance values to start with for R1 and the Potentiometer to give me a wide range of speeds with no load on the motor?

For which Wattage should the Resistor and POT be rated to deal with the currents correctly?

Thanks in advance!
 

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That circuit won't do anything. The resistors are simply another load on the 12 volt supply.
 
Yeah, I realized that. It could work if you limit your current at the power source, but that will over complicate things.

I'm rather going with a simple 555 Pulse Width Modulation circuit...
 
first of all yes for high amps a pot will be a waste of energy you have to use switches like transistors, the other thing the device needs to be in series with the motor , you circuit as you probably realized by now is in parallel with the motor so the motor would still go full speed.
 

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