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I have 2 RD-ZD-25F, 220V/50W DC motors from 2 broken bread-making machines. Can they be used as a generator? I gave one with the hand few spins and I got a little bit of a shock from it.

Thanks

PS: The only specs I could find for it: Model: RD-ZD-25F Voltage rating: 220 VDC Current rating: 0.23 A Power: 50 W Motor diameter: 63 mm Motor length: 105 mm Shaft diameter: Ф7 mm with jam 14 mm Shaft length: 20 mm Wiring: 2-way cable Motor mounting: 3 x openings M3 mm Body material: metal Application: used in bakeries and ovens

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  • \$\begingroup\$ I think you've already answered your question even before posting it. You gave the shaft a spin and got an electric shock - therefore yes it can be used as a generator. \$\endgroup\$
    – brhans
    Commented Jun 3, 2015 at 18:49
  • \$\begingroup\$ Indeed, the issue is that, with a voltmeter, I get voltages from 10 to 190V (different because of different RPM) .. and how can I make it more constant (lets say 12V)? \$\endgroup\$
    – Sorin Trimbitas
    Commented Jun 3, 2015 at 18:55

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Your motor is a permanent magnet DC type so yes, you can use it as a generator.

The permanent magnets create a fixed field strength. Since the voltage generated in a wire is proportional to its rate of movement through the magnetic field, the motor will produce higher voltage at higher rpm. To get constant voltage out you have two options:-

  1. Spin the motor at constant rpm.

Depending on what mechanism is driving it you may be able to use a centrifugal governor, CVT or variable pitch blades to adjust the speed.

  1. Regulate the output down to a lower voltage.

You could try using a switched mode power supply that is designed for eg. 90~230V input and 12V output.

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  • \$\begingroup\$ Thank you! Do you know a switching regulator? (I looked on analog.com and couldn't find one with Vin max > 30V) \$\endgroup\$
    – Sorin Trimbitas
    Commented Jun 4, 2015 at 15:28
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    \$\begingroup\$ Look for "off-line switching regulator" or "SMPS controller". Alternatively you could modify a commercial switching power supply, or scavenge parts from an surplus device that has one in it. \$\endgroup\$
    – Bruce Abbott
    Commented Jun 4, 2015 at 20:13

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