How to turn a brushless DV motor into a generator?

Turning a DC motor into a generator looks like very straightforward: mount and forget.

However, in the case of low-power projects (mine is a small desk-on vertical axis wind turbine) there are some question marks:

  • friction of brushes may reduce power
  • there is a need to spin the motor at faster rpm than when used as motor

At least that I could find.

On the other hand, brushless motors are smaller at the same power and I suspect they present lower friction.

If I get it right, brushless motors output three-phases - alternative current that can be converted to DC.
Some people on the net suggest a Shotkey diode rectifier to achieve this.

I found schematics but not sure they are effective at a small rpm (say 200- 500 rpm) considering that the Shotkeys do have a voltage drop, although very small.

Some info I found:

Still pending questions - no answer from browsing the internet:

a) how difficult may be to find, mount (or build?) a specific controller? Can be done via hobby resources/Arduino - if needed?
b) what is the minimal rpm to get some useful vortage out of this type of motors> By minimal - I expect some 1V - which is good for a Joule thief circuit to operate?

Thank you very much for your kind and patient help!

Circuit of 3 phase generator from a brushless motor.png


I am now working on the vertical axis turbine - very fun :slight_smile: It is some 50 cm high and 20 cm radius. Two designs: a) classic 3 or 4 wings Savonius and b) Helical shape. If I will find a detailed Darrieus drawing, maybe I can go for that as well.

Circuit of 3 phase generator from a brushless motor.png

Still at it, falexandru ?

Spin your fan and see what volts it generates. Then short it out and see what current.

Then you can figure out a controller.


@allanhurst - Thanks! Your suggestion is in line with my usual approach.

I completed the PV charger module (PV and circuitry, most of the mechanics) :-). On the second prototype already.

Now I am on the wind turbine side of the charger. Experiment with the circuitry (inductance: buy or built? Hiw to measure? :-)). Rotor is easy to build. But transmission of the rotation from the rotor to the generator is problematic.

The difficulty with this project resides in the very small scale. Although power is no important (is a demo), the double generator has to work. Namely to light a modest LED :-).

Therefore I am digging into all opportunities to increase the efficiency of the wind generator.