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Wind powered generator using radiator fan?

Discussion in 'General Electronics Discussion' started by wingnut, Aug 27, 2015.

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  1. wingnut


    Aug 9, 2012
    Hi All

    Wind powered electric generators are obscenely expensive. I was wondering if it was possible to grab a car radiator fan (which has a 12V DC motor), face it into the wind, and turn the motor into a generator. All well and good in theory. But most if not all modern radiator motors lack permanent magnets so that when you spin the fan, nothing is generated except a light sweat.

    Is it possible to energise the windings into magnets (like one does an alternator) by briefly applying 12V, and would these windings then stay magnetised for as long as the wind blows?

    Some research on non-permanent-magnet DC motors says that current flows from the stator into the rotor windings via the brushes and that rotor and stator may be wired in series, in parallel or a combination of both.

    I am trying to avoid buying a radiator fan only to discover that it does not work, hoping that someone on this forum may have tried this, or a similar cheap wind-powered alternative.
  2. duke37


    Jan 9, 2011
    I have used an old radiator fan motor to drive a coil winder. I used the back EMF to measure speed so it could be used as a generator. It had a permanent magnet and brushes. I would think that brush friction would be a problem in your application. The torque generated by a small fan would be very low.

    If the motor were separately excited, much of the power would be lost and the efficiency would be low.
  3. Minder


    Apr 24, 2015
    Fan motors are generally P.M. brushed?
    If it it is the rare case where you have a wound field, all you need to do is carefully open up the motor and separate the field coils, and feed them with DC.
    Try shorting the leads together and see if you get braking effect when spun by hand.
    The only other situation for a two lead DC motor is it is BLDC and has an internal controller, but unlikely.
  4. 12vdc


    Apr 13, 2011
    Depending on your year/make/model, most older pre 2000 fans are permanent magnet.
    Radiator cooling fan, heater blower motor, wiper motor and (newer) starter motors.

    The motor you describe sound more like an automotive "alternator". It requires an energy source(12 v ) battery to energise the "field" windings which appear to be permanent magnets to the rotor.
    You could use one and have a "Topped up" 12V battery to draw from. There are many newer efficient built-in regulator type alternators that only require 2 connections (+) & (-).
    Alternators can easily require up to 5 hp of mechanical (rotational) energy to produce their rated output.

    If you are looking to buy a used unit (recyclers) note that due to their exposure to the elements most of the bushing equipped motors seize from inactivity.
    If you wish to "build" your own setup a larger fan will be better.
    If you find a blower motor you probably already know the fan (drum style hamster wheel) is useless.
    If you wish to enhance a fan, placing the blades at the small end of a funnel will increase air speed thus fan/shaft speed.
  5. wingnut


    Aug 9, 2012
    Thank you all so much for your input. The next time I go past a scrapyard selling motor spares I will try to find some old radiator fans which still have permanent magnets. As duke37 found, there should be a back emf, I presume measured when power is cut to the fan. It is that back emf which I want.

    Minder, if I can obtain an old wound field radiator fan, I will try separately energising the field coils. Maybe one could even try energising the fields momentarily or even on a pulsing basis, and there may be a net return of energy in windy conditions. But this will require experimentation. I spent the morning taking apart a cordless screwdriver which had a brushed permanent magnet 4.5V motor. It did push out DC when spun. Now I will have to visit my favourite "mall" the scrapyard, to see if anyone has thrown out an old fan so I can commandeer its blades.

    And as you say 12vdc, car alternators take some heave to get them going. I currently have a Bosch alternator driven by my exercise bike which pumps out up to 55 amps in theory but I can only pedal out 80 Watts. I need a much weaker generator/motor because, although the wind can really get up here, I don't want a giant fan on my roof killing wildlife and frightening neighbours.
  6. duke37


    Jan 9, 2011
    Another problem with brushed PM motors is that the cheaper ones have the rotor windings in slots parallel to the rotor axis. This means that the motor will jerk from one slot to the next, this is known as cogging. A certain amount of torque is required to start the rotation and there will be a minimum speed below which the motor will stop.
    Cogging can be eliminated by making the slots in a helix but this is more expensive and is not necessary in an automobile motor.
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