Controlling a DC motor speed with a potentiometer

piscis · Jun 20, 2006

I find this hard to believe that a colleague of mine was telling us that he could control the speed of a small 24vdc motor (about 1/50th of a HP) with a Potentiometer? (I’m not sure if he meat a brush or a brushless type though)

Question: It this possible?

rsdoran · Jun 20, 2006

Yes, a potentiometer can vary voltage or current which can vary speed. The potentiometer must be have a watt rating that will handle the current involved.

Take a look at this page: http://www.patchn.com/DC/DC_15.html

piscis · Jun 20, 2006

rsdoran:

You mean this is true regardless of motor brush or a brushless type?

rsdoran · Jun 20, 2006

piscis said:
rsdoran:

You mean this is true regardless of motor brush or a brushless type?

NO I did not state that. Your question asked if a potentiometer could change the speed of a DC motor, yes it can.

A brushless DC (BLDC) is another issue:

The Brushless DC motor does not operate directly off a DC voltage source. The Brushless DC motor has a rotor with permanent magnets, a stator with windings and commutation that is performed electronically. Typically three Hall sensors are used to detect the rotor position and commutation is performed based on Hall sensor inputs. The DC Brushless motor is clean, fast and efficient, and creates no sparks, making it a safer choice in explosive environments. The linear current/torque relationship results in smoother acceleration. In sensorless control, back EMF zero crossing is used for commutation. This motor type has a longer life than Brushed DC motors.

Another definition:

A brushless DC motor is electric engine where the stator is a classic 3 phase stator and the rotor has surface mounted permanent magnets. It is equivalent to a reversed DC commutator motor, in which the magnet rotates while the conductors remain stationary. BLDC motor has no commutator and brushes, it requires electronic control for operation. They often have external position sensors used by control unit, but sensorless control is also possible.

An animation of a 4 pole brushless DC motor: http://www.servomag.com/flash/4-pole/smi-motor007.htm

Is it possible to control the speed of a brushless DC motor with a potentiometer, YES but not directly. A BLDC controller/drive may take an analog input, provided by a pot, and convert it to the necessary speed signal.

You need to take time and phrase your question(s) with the details that address the information you are looking for.

Controlling a DC motor speed with a potentiometer

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