DC Brushless Fan - Speed control

Thread Starter


Joined Jan 9, 2009
Hey all,

just curious how some of you might go about trying to vary the speed of little cheap 24V DC Brushless fan.

I assume the built in electronics are trying to do some form of speed regulation and using some cheap form of feedback, so just dropping the voltage to 12V might actually just end up at the same speed (assuming back emf doesn't stall it).

Any insight into a low cost solution to vary a cheap little brushless fans speed?

I am accustomed to controlling the switching myself but am trying to think of the best way to do it with low cost fans.

Thanks in advance.


Joined Feb 28, 2009
The ones I have taken apart have a hall sensor near the perimeter of the printed circuit board and a magnetized ring glued to the inside of the cup shaped rotor. The magnet, in association with the hall device controls commutation as well as supplying the PM field for rotation. With lower voltage, there is lower torque and the combination of torque and load regulates speed. The commutation just makes sure it goes the right direction by firing voltage to the coils at the right time to attract/repel the magnetic ring.