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Motors used as generators

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Johnson777717

New Member
Hey folks!
I have about 10 small motors around that are collecting dust. I was thinking of rigging a self powered light, for those times when the electricity in the house goes out, or for camping, or have the ability to connect a small fan etc. Using a flashlight is too easy!!! :D

What I'm thinking of doing is taking a plate of sheet metal, then fastening the small motors onto the plate ofset from each other. Then running a rubber drive band across all of the motors. This rubber band will be connected to a hand crank device which provides the pinion for the motors.

I want to connect the motors into a circuit that will provide sutiable voltage and amperage to light a small light bulb or small LED array.

My question is with the voltage and current generated by the motors. Most of the motors are different sizes, and therfore will provide different amounts of current and different voltages. What do you think is the best way to bottleneck these motors down into one Voltage and current?

Then I'll be able to walk around my house, like a dork, cranking a box of motors! :shock:
 

Dean Huster

Well-Known Member
Motors as generators

I think that you'll find that one of the larger motors will be sufficient for powering a #222 lamp (the "headlight" of a Weller soldering gun or the lamp in a 2-cell penlight). Rubber bands make absolutely awful "belts" because they're too elastic. And a dozen motors to power a light bulb seems a bit cumbersome, but the general idea is good. The trick is to set up a gearing system to get enough RPMs to the motor.

If you couple the shafts of two fairly-healthy identical dc motors and power one from its normal voltage source, it'll drive the second one as a generator. If you short the leads of the generator, you'll nearly stall the shafts, so you know that a lot of power is making the transition from electrical to mechanical and back to electrical. I have a few 12v motors that measure about 3.5" long and 2" in diameter, and they make darned-good motor-generator combos. I wouldn't hesitate to use one of them as a windcharger generator for a small, outlying project, such as a weather data gatherer.

Dean
 

Dean Huster

Well-Known Member
Steppers As Rotary Encoders

Charles has some good stuff on his site (techlib), but still, he hasn't used a stepper as an INPUT device! If you hook an oscilloscope to one winding of a stepper (center tap common, CH1 to one side, CH2 to the other), you'll see that a stepper has a quadrature output. Using the tap as ground, send each output to a comparator to square up the signal, then use electronics to detect direction and speed and the final output can be used on 74LS193 counters to count up and down using a rotary control. It can be a very handy input device, cheap compared to buying a modern rotary encoder, and just a lot of fun to play with. Downside is that it takes a bigger stepper so that it can still put out a higher voltage with slow rotation -- the little steppers just won't get it, no matter how sensitive you make the comparators. And no matter what, really slow movement will be missed by the comparators. It is a lot of fun to play with, and regardless of how "unfeeling" everyone seems to want the digital world to be, there ain't nuthin' like the tactile feel of a stiff stepper motor with a knob attached to the shaft for input control, especially if it's a crank-type knob from the "old days", using it to control the frequency of an oscillator or receiver.

Dean
 

Agent 009

New Member
Maybe if you connect the output of the motors to a non-inverting input of an OpAmp, have the inverting input grounded (in this case, the '-' (minus) terminals of the motors), and have a 1k resistor as negative feedback, maybe you should get a Voltage buffer, allowing for consitency b/w the different motors...
 
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