Nice little motors on eBay

[Gotwind Ben]

I often keep my eye out for suitable DC motors to be used for wind turbines.
This one is very small, but is brushless, a bonus and would cut in at around 436 rpm.
I may be wrong, as these are electronically commutated? - not sure how you would get the power out :?
http://cgi.ebay.co.uk/DC-Brushless-Moto ... 7314038281

Nice find Ben, thanks for sharing. I also keep an watch on DC motors on ebay but have never seen one like this before. It appears to have a lot of wires coming out, looks like a red and black which I guess would be the power input and then another bunch of wires which I guess are something to do with the speed control?

I think the "electronically commutated via feedback hall sensors" part doesn't matter if using as a generator provided you can get at the internals to see how its wired.

Would be interested to know what magnets are used and to see the inside of one.

I like the low cut in speed, looks like a promising motor for DIY.

Regarding suitability:

http://www.scoraigwind.com/books/marty.htm

I would be interested in looking at the circuit these motors use for commutation. As the drive circuitry obviously doubles as a synchronous rectifier, it might be interesting to investigate a similar circuit for general three phase rectification. While diode losses are not huge, if they can be reduced all's the better! For instance, using standard diodes with a 1.3V drop, @ 10 amps per phase this implies diode losses of 13W per phase. While this is trivial for a 220V system, in a 12V system, this could be as much as 10%. Replacing diodes with a synchronous rectifier using low Rdson mosfets could reduce the losses to the mW range in a 12V system.

I will add this to my "to do list" :D

Fish

[Gotwind Ben]

Agreed.
Rectification losses at such low voltages (a 12v system) has always been a hurdle or challenge.
If there is an alternative, e.g a synchronous rectifier using low Rdson mosfets that would be great.

I'm pretty sure someone may have looked at this, maybe the cost is prohibitive, however, I would happily pay 100% more for a better, less 'lossy' rectifier (within reason, $20 compared to $10).

I'm sure Ghurd (Glen Hurd) would have some positive input on this subject, I don't think he calls in here very often though..
I dont want to stray to far off topic but b.t.w Fish, Have you seen Glens Dump, or Shunt, Controller that uses power FET's - very nice, works a treat and reasonably priced (no affiliation).
http://www.ghurd.info/

A precursory look makes me think the only thing preventing synchronous rectification using mosfets in DIY alternators would be complexity. The brushless DC motors use Hall Effect switches as sensors, and the placement of these switches in the stator would require some thought and testing. It's kinda like the notion of using relays to switch the coil configurations based on output voltage to achieve lower RPM "cut-in" and higher amperage at some specified higher RPM; certainly can be done, but kinda complex for the average DIYer.

Yes, I have seen Greg's charge controller, very nice piece of work! Many of the parts he sells are below low quantity prices from suppliers like Digikey. (IRFZ44N: Greg = $1.00 Digikey: 1 = $2.04, 10=$12.60, 100=$92.17).

Fish

[Gotwind Ben]

Continuing the search for an ideal alternator/motor for DIY wind.
This Chinese made unit interests me.
Coreless (No iron core), 350 w Max with a diameter of just 138mm (5"), I wonder how they managed that at such a small scale?.
Prehaps their "A good combination of modern technique and Chinese art" statement :lol:

It must be some kind of radial coreless design (somehow) - 91% efficency is quite a claim also.
I want one to play with :D
http://www.alibaba.com/product-gs/34836 ... rator.html