DC speed controller

[Clark Kent]

Hi. New to the forum. I need to run a little motor out of a printer. I found a line in a laptop charger is 16v, lowest one. Other line is 32v. Anyway, the 16 will run the little motor just fine.  I need to control that speed. It's either on high or off. Potentiomeeter, or rheostat?  Please explain the choice. Thank you. I'm trying to get some quick education on this. 

[studiot]

9 hours ago, Clark Kent said:

Hi. New to the forum. I need to run a little motor out of a printer. I found a line in a laptop charger is 16v, lowest one. Other line is 32v. Anyway, the 16 will run the little motor just fine.  I need to control that speed. It's either on high or off. Potentiomeeter, or rheostat?  Please explain the choice. Thank you. I'm trying to get some quick education on this. 

Printer motors are often of the stepper motor type as opposed to the continuous rotation type.

Stepper motors require a fixed pulse of energy to advance one step so will not thank you for much variation of voltage in their drive.

Continuous motors can be speed reduced by voltage reduction at reduced power/torque output.

A rheostat is a series device which shares the available power with the load by dividing the voltage, but is susceptible to being damaged by overcurrent at low resistance settings, since it always take the fully current drawn.

A potentiometer is a parallel device that shares power by always suffering the full input voltage but only receives a proportion of the current, ie it divides the current.

Edited April 6, 2019 by studiot

[Clark Kent]

Thanks for responding. If I were to take a shot at it, which to you recommend?  and what do i need to look at when purchasing the pot or stat. what info on them do i need. thanks. 

[Chris S]

I spent a lot of time on a project to control dc pm motors. A pm (permanent magnet ) motor has two wires, and speed will vary with applied voltage.  If you just want to manually vary the speed, buy a cheap adjustable voltage regulator off ebay.  But if you want the speed to be accurate, that is a different ball game.