I need to set up speed control of a small BLDC fan that is not wired for PWM. The only way I know to do this is with a potentiometer, and it's my understanding that it can be done with the pot wired for current control or voltage control. Battery life is a concern, so is either method better for reducing wasted power through the pot - or is there an even better way to control speed? I read an article recently that said PWM was possible for any DC motor, but I don't understand how you would do that with only a 2-wire motor.
Thanks for help to newbies!

 

You can certainly do PWM with a 2 wire load. Considering that PWM varies the average voltage, at worst you would need a filter if the motor doesn't like chopped DC. Either a capacitor in parallel or an inductor in series (or both) depending on which is more practical at the PWM frequency.

Regards
cww