Question about motor(s)

Dear Fellow Wind Techies,

I'm a teacher and we're trying to make-- and use-- a small wind generator. I

was told that we could use a treadmill motor with blades attached to make a

wind generator. We inherited a treadmill, gutted it, and now we have a motor.

When we attached a "fan belt" from a drill to the motor, it put out -25.13 volts**

(**emphasis on minus voltage.)

QUESTION: Will this 120 volt motor work for making a 12 volt DC wind generator

without using an inverter?

QUESTION #2: If not, what's our next best CHEAP option? Unlike what many

think, my pockets aren't lined with gold...!

QUESTION #3: Does someone have a small (125 watt?) wind generator they

would kindly donate to my class so I can teach wind technology?

Thanks for your replies. Please e-mail me at

Regards, Mark in NH


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Question about motor(s)

    Motors don't make the best generators.

    If you want to research home-made wind generators a good place to start is

    You might be better off with an automotive alternator for a starting point.
  • kenputerkenputer Solar Expert Posts: 27
    Re: Question about motor(s)

    If you want to charge 12 volt batteries the motor can be made to do that,you will need a blocking diode so the battery wont run the motor.
    A car alt. is the last thing you want to make a wind generator,best is high voltage low rpm PMDC motors for your project.
  • System2System2 Posts: 6,290 admin
    Re: Question about motor(s)

    Thanks for your reply. So where do I locate a PMDC motor at low ot no cost? What applications are they used for? Will the treadmill motor my students 'parted out' work (understanding that we need to use a blocking diode or a rectifier.)

    I understand that car alternators require a much higher RPM before they output useable voltage. Is that accurate?

    What size turbine blades should we consider, and how many? Are three blades really better than six blades?


    Mark in NH
  • BB.BB. Super Moderators Posts: 26,666 admin
    Re: Question about motor(s)

    Three blades is probably "optimum" for heavy wind conditions (actually 2 is better and 1 blade is best in theory--but there are lots of technical reasons that those configurations are not usually used)--but for smaller systems with lower towers (and lower average wind speeds), a few people here report that changing to more blades increased low to mid range wind speed power output.

    3 Blades vs 5 Blades

    Any spinning blades and "heavy" turbine mounted 30-60+ feet in the air can be dangerous (a good 30+ MPH gust on a lightly built system can send blades flying, collapse the tower, cause the yaw bearings to fail, etc.). So always keep people away from the system and, probably avoid unattended operation outside of class hours (and during forecasts of heavy winds) unless the turbine is in a fenced area.

    You probably can use the treadmill motor to build a demonstration/educational unit to show principles.

    Assuming it has 3 wires out and is a 3 phase PM motor--You can throw a rectifier bridge on the output and spin it with a variable speed electric drill to see how fast you need to spin (use some sort of RPM counter) it to get ~14.5 volts and a useful amount of current.

    If the motor outputs -25 volts at speed--go ahead and attach it to a car battery with a voltmeter and current meter and monitor it's output. And see if it provides useful current (watch the current flow and do not exceed the motor or amp meter current rating).

    Place a Kill-a-Watt meter on electric drill. Spin the motor at required RPM both loaded (charging the battery) and the drill unloaded (at same RPM). The readings from the Kill-a-Watt meter will give you a rough idea of how many watts are needed to spin the PM motor at a given RPM/load.

    Now you can use that information to size the blades for your needs and average wind conditions.

    Be aware that the treadmill motor is not weather proof and the bearings probably cannot take end thrust and the weight/rotational mass from the blade assembly/wind loads for long term operation--but it should be OK to demonstrate the principles.

    Some people use a belt system to isolate loads--but there can be fairly high losses through a belt transmission system.

    The link that Marc provided should have enough information for you to begin your design and they also have a forum to ask questions.

    While we always like to help--They probably are much better equipped (in general) to help you with DIY wind.

    Another place to check through would be for DYI wind information (and other solar RE projects).

    I just want to emphasis again that Wind Turbines can be dangerous and you should assume that any turbine (but especially DIY) can fail. From this thread:
    Originally Posted by BB.
    "energetic disassembly"


    Haha I love that term. Perfectly describes my first attempt at a "home made" wind turbine. Spent weeks forming a beautiful 14 foot long blade of wood. Was shocked by the power it produced. Then I came home one wk-end and found a six foot portion of the blade sticking out of the barn roof, where it had been driven in like a giant knife.

    Except for a one foot long tip, the rest of the blade was never seen again.
    Now I know it had been subjected to "energetic disassembly". Haha
    Be vary careful when doing this project around kids.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • KevinbKevinb Solar Expert Posts: 26
    Re: Question about motor(s)
    BB. wrote: »
    Be vary careful when doing this project around kids.


    I second that.

    Don't take this wrong Mark, but it doesn't sound like you know enough about DIY wind turbines to build one that would effectively teach wind technology, as you stated your intention was. If youre trying to teach how to build things, that's a different story.

    Could you come up with $100 (bake sale, etc.?) If so there is an educational kit called Wind Pitch (no affiliation) that might be good for you and your class. Good luck-
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Question about motor(s)

    An interesting update on my first and only attempt at a home made wind turbine and it's "energetic disassembly" that Bill reminded us of: This past Summer, the nearby lake was drained down to it's lowest point in 40 years. Of course out of curiosity, several of us went exploring the newly revealed land. Believe it or not, at the waters edge I came across a two foot tip from the other end of the old blade, the green paint still on most of it! Apparently it had landed in the lake, became waterlogged and sank, where it remained for almost 30 years! What caught my attention was the green paint, and after studying it's shape, it finally dawned on me what it was. The wood was still almost as good as the day it was subjected to that unfortunate "energetic disassembly" so long ago. Never in my life had I ever expected to hold it in my hand again, but the lake had preserved and handed it back to me. And now water from that same lake is powering the computer that's sending you this message. Life can surely take some strange and unexpected twists!
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