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Attached a 9vdc motor to an LED to simulate a simple "generator" and I can get it to illuminate by swiftly spinning the motor in quick bursts, but if I connect a drill to the motor so there's a constant spin, the LED doesn't illuminate at all. Why is that?

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    \$\begingroup\$ Is it spinning the wrong way? The motor will generate the wrong polarity. Try reversing either the direction of spin, or reversing the connection to the LED. \$\endgroup\$ – Steve G Apr 5 '16 at 21:07
  • \$\begingroup\$ Or you haven't restricted the current and you've blown the LED. Add a 1k resistor between the motor and the LED to limit the current to < 10 mA or so. \$\endgroup\$ – Transistor Apr 5 '16 at 21:10
  • \$\begingroup\$ I have it connected + of motor to anode of LED and cathode to - of motor. So you're saying when I spin it by hand, when the spin stops that's when it's illuminating? I'll try switching the wires \$\endgroup\$ – ohmmy Apr 5 '16 at 21:11
  • \$\begingroup\$ @transistor I don't think I've blown it because still lights up when I spin quickly by hand \$\endgroup\$ – ohmmy Apr 5 '16 at 21:12
  • \$\begingroup\$ Good. + and - depend on direction of rotation as Steve G pointed out. \$\endgroup\$ – Transistor Apr 5 '16 at 21:19
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A DC generator's output voltage maximum is proportional to the speed at which it is cranked; possibly you need to get a faster drill, or drive the motor shaft indirectly. You can gear up with a rubber wheel in the drill, such as some sanding drum attachments, or from a large-radius pulley with a rubber-band belt.

It takes two or three volts to make a simple LED shine brightly; some LED lamps are actually multiples in series, can take more than that. If you can get a voltmeter, look at the generator output, with the LED connected, for the spin-by-hand and the spin-with-drill setups. A series limit resistor (1k ohms) is a good precaution against overdriving the LED while you experiment.

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  • \$\begingroup\$ I have yet to meet the small DC motor capable of killing an LED. I've done this many times, and never killed an LED, and never used a series resistor. The motors just straight up suck at being generators. \$\endgroup\$ – JRE Apr 5 '16 at 21:36
  • \$\begingroup\$ Interesting with the drill on its fastest speed it only measures 1v. When I do quick bursts it reads anywhere from 2-5v momentarily \$\endgroup\$ – ohmmy Apr 5 '16 at 21:48
  • \$\begingroup\$ It sounds like your drill isn't fast enough. 1V will not light an LED. Depending on the color of the LED you will need 1.5V to 3V. As Whit3rd suggested, try to gear up the speed with a rubber wheel on the drill driving the motor. \$\endgroup\$ – Steve G Apr 5 '16 at 22:10
  • \$\begingroup\$ What kind of gear ratio would I need? As in would the drill need to have a bigger gear attached to it and a smaller diameter to the motor? \$\endgroup\$ – ohmmy Apr 5 '16 at 22:48

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