2015-09-18 Hand Cranked Flashlight

I’ve been getting close to finding a  motor to use as a generator for a hand cranked flashlight.  I found one a few months ago, which even included a crank. But the crank was small and hard on the fingers.

This one from Electronic Goldmine (apparently they’re sold out) has a motor and gearbox, with a shaft for a crank.  The shaft has a flat for mounting a crank with a setscrew (see photo).
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I don’t have such a crank so I used a mini vise grip for a makeshift crank.  With the 1 watt white LED connected to the two contacts (white disk with wires), I can crank at a reasonable speed and get a nice amount of light output.  The LED gets barely warm, which means to me that it’s not getting a full watt of power from the generator.  But it’s enough to light the LED and use as a flashlight.  A better and lighter crank might help to increase the output.

I checked Goldmine website and couldn’t find any of the ones I bought. The gearbox makes it much easier to crank. But a small wheel from a caster might be used. The motor can be mounted so the shaft is pressed against the wheel and driven by friction. The wheel is then spun manually. The size of the wheel determines how easy it is to spin. It helps if the shaft has splines or is not smooth, so it doesn’t slip when the wheel turns.

I have also had some success with rubbing the shaft on a rubber or non-slip surface. The best example of this is a bicycle light dynamo. A dynamo (or stepping motor) will generate AC, which has to be rectified to make DC. But it can be driven in either direction. So a back and forth motion on a soft surface will drive a LED, if a 1000 if or more filter capacitor is across the LED, and rectifier or full wave bridge rectifier is used.

Another way of generating AC is to use the head positioning stepper motor from a CD drive. These have a shaft with a spiral groove in it. They will light a LED when the shaft is spun by rubbing on a bike tire or other similar surface. It’s not difficult to light a LED brightly with any small motor.

I have also had good results using a stepper motor from an ink jet printer. These drive the print head and sheet feeder. Stepper motors from other devices such as CD drives work, too. I found a YouTube video where a guy gets 10 plus watts from his hand crank generator with a stepper motor, rectifier, filter capacitor and control box. This is used to charge a cell phone. He has to crank it fast to get the full 11 watts, so a more realistic and easily done output would be 5 to 6 watts at 5 volts, which is about what a cell phone charger puts out.

One problem with these chargers is they require you to hold them with both hands and crank continually for a long time. The generator should be mounted (or mountable with a clamp) to a stable object (like the edge of a table or workbench) so that it can be cranked with one hand and leave the other hand free to do other things. A good way of mounting odd shapes is to use a hose clamp. These could be small or as big as a radiator hose clamp.

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