Motor math

System
System Posts: 2,511 admin
in Wind Power Generation #1
Ok, so i pulled out a motor from a tredmill.

Im confused on the math so im not sure if it will work for a windmill.


P.M.D.C McMillan
Icon M-147891
18 Amps
6700 RPM
CW rotation
Ins Class F
OPen const
1.5HP cont duty @ 95VDC

Will this work? what RPM are we talking about?
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #2
    Re: Motor math
    Prinler wrote: »
    Ok, so i pulled out a motor from a tredmill.

    Im confused on the math so im not sure if it will work for a windmill.


    P.M.D.C McMillan
    Icon M-147891
    18 Amps
    6700 RPM
    CW rotation
    Ins Class F
    OPen const
    1.5HP cont duty @ 95VDC

    Will this work? what RPM are we talking about?

    Well a few things.
    First, is this a PM motor?
    Second, at almost 7,000 RPM, it "ain't gonna" last long in wind service, will need quite the gear box to bring the revs up, and then you might be lucky to get 10 amps @ 60 volts.
    Third, if you slow it down to a "reasonable" speed, both the voltage and amps are going to drop way off, so it's usefulness really depends on what power output you're looking for, or expecting.
    Finally, if you're thinking of attaching blades directly to the motor shaft, consider that it's bearings were never designed to be subjected to such stresses. Oh, and how ya gonna keep the rain out?
    At 1500 RPM you might get 1.25 amps to charge a 12 volt battery. Just very rough, off the cuff estimates. You'd have to test to verify.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: Motor math

    Motors aren't generators. They don't work very efficiently "in reverse".
    Motors also aren't designed to sit out in the weather.
    Even commercial small wind turbines suffer from low output and short lives. Often because of poor site evaluation.
    Not saying it can't work, but don't expect much power or longevity.

    For lots of good info on DIY wind power check out Otherpower.com: http://otherpower.com/
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  • System2
    System2 Posts: 6,290 admin
    #4
    Re: Motor math

    Ok well thank you for your replies.
    Can you help explain the numbers?

    I know if i turn it with a drill i can get 16V on high my "19v craftsman cordless drill" I think its like 2500 rpms :confused:

    Teach me to fish..... so i can learn how to catch my own....
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #5
    Re: Motor math
    Prinler wrote: »
    Ok well thank you for your replies.
    Can you help explain the numbers?

    I know if i turn it with a drill i can get 16V on high my "19v craftsman cordless drill" I think its like 2500 rpms :confused:

    Teach me to fish..... so i can learn how to catch my own....

    To have it put a charge in a 12 volt battery, you have to crank the revs up till the no load voltage is about double the battery voltage. Considering that a 12 volt battery commonly charges at 14.5 volts, that's about 30 volts you need from the charging source with no load. As soon as the battery is connected, your "generator" will drop to battery voltage and begin to charge. Since you need about 156 RPM per volt output, indications are that you'd need to crank the speed up to almost 4700 RPM to charge the battery, but the amperage will still not amount to much.
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