Electronic Circuits and Projects Forum

Not sure what you mean here, are you intending to limit the speed by using the motor as a brake? This is always a bad approach for wind generators, nature can throw more energy at it than it can handle. A better technique is to feather the blades, and allow the force of the moving fluid to pass through.

The linked motor is rated ~ 11V 20A (= 220W) so I don't see why you can't run it as a generator and draw up to 20A from it to give the required braking effect, providing the turbine isn't producing more than 220W power. A power FET operating in PWM mode could easily handle that current and drive a suitable resistive load. The motor also inherently gives you an output voltage proportional to speed, so can be used in a feedback loop for speed control.

I have looked at ESC for airplanes but I am not sure if they work with a generator.

I'm pretty sure they could easily be adapted, using a resistive load instead of their usual motor. Are you planning to use an off-the-shelf ESC or build one?

You are aware the those little motors normal run at 10,000 - 20,000 RPM to put out their rated power.

Going from 25 RPM to 10,000+ RPM is not practical or likely even possible on a small scale home built design.

Your better solution would be to use a much larger and slower DC motor for your generator.

A laarger 1750 RPM 180 volt permanent magnet motor spinning at roughly 120 RPM would be a much more practical way to go if you are after a 12 volt output.

Although more costly on the motor end a common 10:1 gearbox or chain or belt drive is way easier and cheaper to deal with in the over all design.

If you are just looking to produce a braking torque effect I would recommend a common hydraulic pump or motor as the driven load source.

They are compact, sealed to the level of being submersible and water proof, capable of working at high torque loads at very low RPM's, and are easy to work with having only one line in and one line out.

cloakinghalk - for that you could just connect the windings across an adjustable resistor. Try going from open to shorted first, and see if this gives you the range you need for your vorticity experiments.

Duffy- So I tested shorting out and using resistors across a brushless motor and it did nothing. I couldn't feel any difference. I was going at a slow speed though. Do I need to go as fast as the operating speed of the motor?

Yes, nothing happens at slow speeds with (almost) any generator.

See that idiotic "kv" rating on the spec sheet? I HATE the term. HATE IT!!!! "Kv" means "killivolts"!!!! Some jerk decided to use this instead of RPM/Volt, which is what the spec really means. So, for your motor's 850 RPM/Volt rating, at 9.6V, it would be running around 8,160 RPM.

I don't know what the pitch of your prop or your flow rate is, but you aren't going to notice much spinning this or almost any other motor by hand without gearing. Get it spinning a few hundred RPM and THEN short the windings.

Here - this is a brushless ESC I built that you could feel the braking action on spinning it by hand. See how it's geared?
Attachment 60916

Edit - gone now? Who keeps killing my pictures on this board?

So, I'll try again - to help OP see how big the gear ratio needs to be:

Attachment 60925


Edit: Gone again. Why?