PWM control motor

[luggsy]

as title I am looking to fit one to a brushless 12 v water pump , some PWM say they are not for a brushless motor ? Can any one tell me why? And recommend a suitable PWM control motor for a brushless motor thanks in advance

[youthoftoday]

I don't know much about boat equipment, but... motors with brushes take DC and feed it straight into the coils. The brushes take care of switching polarity to stop the motor just oscillating back and forth.

 

Brushless motors require an external driver to switch the polarity of the current (or do something more complicated). This may be built into the motor. These probably expect a constant voltage in order to get their timing, current driving, etc right.

 

A PWM controller varies the duty cycle of a pulsing DC voltage in order to limit the amount of power. I would imagine that it would be quite happy driving a 'predictable' coil load, but would interfere with the electronics that drive the brushless motor.

 

(I could be wrong)

[Chalky]

Small brushless motors of the type you're talking about have a circuit built in to them that switches the power to the motor coils in an order that causes the rotating part of the motor to rotate. Very simplistically its doing what the brushes do but its doing it electronically. If you PWM a brushless motor you'll cause problems for the electronics. Because of the way the controller works you can often control the motor speed by sending a command to it to vary the speed. This is often via a variable resistor or a varying voltage.

[nicknorman]

Small brushless motors of the type you're talking about have a circuit built in to them that switches the power to the motor coils in an order that causes the rotating part of the motor to rotate. Very simplistically its doing what the brushes do but its doing it electronically. If you PWM a brushless motor you'll cause problems for the electronics. Because of the way the controller works you can often control the motor speed by sending a command to it to vary the speed. This is often via a variable resistor or a varying voltage.

 

The small brushless motors in a couple of pumps I have, vary their speed according to the input voltage - as you say, obviously looking at the voltage to decide the coil switching frequency. However I don't think we should dismiss PWM control for these since a decent PWM controller has a smoothing circuit such that, whilst the guts of it are switching on and off, the resultant output is smoothed into a reasonably steady voltage. There will obviously be some ripple but how much will depend on the particular PWM controller and the current taken.

[ditchcrawler]

I have some small computer fans, 12 volt and the boat is 24 volt, 2 in series was a bit to much blow so I put 3 in series and that seems OK, so effectively reducing the voltage to reduce the speed. 8 volts each + a bit when the engine is running