Need help choosing a treadmill motor

OK...I've read all I can read regarding the best treadmill motor to use for a windmill. From what I can understand low RPMS & high voltage is best. Correct?

When I look on ebay for a motor I see motors with RPM ratings at 5600 and up. Surely that doesn't mean you need 5600 RPMs to gen enough to charge your bats does it? If not, how can I be sure which motor to use. Any help you guys could send my way would be appreciated.

OK I think I found the formula...someone correct me if I'm wrong...I take the voltage of the motor, say 120V divided by the rated speed of the motor, say 5600 RPM. That gives me .0214. That is volts per RPM? OK so if I multiply that (.0214) by a number...say 600, that would give me an output voltage of 12.84 @ 600 RPMs?

Is that correct?

If that's the case, this motor isnt really what I want. Something around 300-400 would be ideal. Correct?

[Gotwind Ben]

Correct, sort of
Remember the motor has to be of the permenent magnet type.
Divide the rated rpm by its rated voltage
e.g. 4000 rpm/ 120v = 33 rpm per volt.
Multiply this by maybe 14v for a cut in voltage to charge a battery, 14x 33 = 462 rpm
allow maybe 20% more for losses, so around 550 rpm to reach a charging voltage.

This is quite high, any decent power would require considerably more rpms, maybe 800 rpm, dependent on the prop, speeds in this area would be less than 4' in diameter, and a 2 blader - there's lots more to it than that, but in general.

The DC motors on eBay and the like are o.k for starters/ learning, but by no means the best solution, treadmill motors from experience are only any good for 6v battery charging.

Hope this helps.

It does help. Thank you for your reply. I think I can safely buy a motor now without getting a dog.

Keep in mind how voltage per RPM is achieved...
Lots and Lots of turns of wire,
meaning smaller wire with more resistance.

This is not correct, but it is sort of a ball park idea...
Name plate Volts / name plate Amps = Ohms(sort of)

I look at the RPM mathematically required to get about 27V.
Then take 12 / Ohms(the sort of ohms from above) = Amps I could expect to get into a battery at that RPM.

Again, it is not correct, but it is closer than what most ebay sellers say.
Consider it a method to compare one motor to another.

One flaw is some motor name plate amps are completely unloaded, maybe 0.12A.
The exact same motor for another buyer may be name plate rated for 12A.
These cases are when the best guess is derived from using the HP rating to find the missing data.
Treadmill motors are a bit different than higher grade motors. Most seem to show the max rated current.
G-

hey ghurd,

where have you been hiding that "formula"? never seen it before.
thanks for that.

cheers, dave

I made it up myself. ;)
It is condensed 50:50 mix,
based on known formulae, :ugeek:
and
derived from my personal experience of buying and testing 100 nearly useless motors for windmills.
:oops:


Like I said, it is not exactly right, but beats buying something blindly, or because of a well placed deceptive sentence on ebay.
G-

Like I said, it is not exactly right, but beats buying something blindly, or because of a well placed deceptive sentence on ebay.
G-

That's a good point. They can say just about anything they want. OK...so if treadmill motors are iffy at best, what is a good source for motors for windmills?
I bought the carbon fiber blades off ebay. After reading about them, they seemed to be about the best and didnt want to try my luck at PVC or have them come apart in a high wind. I might stick to the treadmill motor for version 1.0 of the windmill then upgrade when i not such a newbie. Just for reference, this is where I did most of my reading on wind turbines 'missouriwindandsolar.com, That's the blades I bought.

I wrote a short little article about how to choose a motor:

http://www.windynation.com/web/choose_a_motor

In my opinion, it is a very good article for the beginner. If there is anything you think that I should add, let me know. Keep in mind that this is an introductory article for the beginner and, as such, I want to keep it very simple. WN

WN, that's a great article. It really simplifies it for the newbie (me) so they can understand or at least make an educated purchase. I went to ebay one day specifically to buy a treadmill motor and gave up because all of the different RPMS, volts, amps and I really didnt know what I needed. This board and your article really helped. I think what I'm going to do is look at whole treadmills and see if I can get lucky finding a decent motor in one. They usually sell for around $50 - $75 here. Im at a standstill w/o a motor. Thanks again!