When ever I took apart old equipment like dot matrix printers that were heading for the trash heap I saved the stepper motors, slide rails, etc… I have tried using the stepper motors in projects like making generators, but you have to spin them fairly fast to get any useful voltage out of them, so I never did much with them other filling up a box in the garage.

Since I have been playing with the Joule Thief and low Voltage energy harvesting experiments, I thought well lets see what we can do with a stepper motor. So I took one of the stepper motors out of the garage this morning and made a circuit with a stepper motor that has both coils connected to two bridge rectifiers feeding a 8200uF 10VDC capacitor. The capacitor then feeds a Joule Thief circuit that is running 4 white LEDs in series. The generator is able to light the LEDs at very low RPM. ( I stopped at 4 LEDs because this is around the target voltage I would like to use this circuit at which is 14VDC, I am sure that this will run more LEDs in series.)

A Joule Thief is a perfect circuit for this application. The circuit is a simple 3 component, low voltage DC-DC boost converter. The circuit can run on voltages as low as 300-400mV depending on the transistor used and windings on the transformer. Specifically in this application I am rectifying the low output of the stepper motor and storing the energy in a capacitor then using the Joule thief to boost low voltage stored in the capacitor to about 14VDC. The final application for this Joule Thief circuit will be to charge 12V sealed lead acid batteries using a low speed windmill.

So here are some applications this could work in (be aware that these circuits would have to be redesigned with some protection to prevent failures):
* Low wind speed generator.
* Low speed water generator using a water wheel setup or a small Pelton wheel with low water head.
* A machine that converts linear motion to rotary motion could also use this type of setup (like the old sewing machines that were run from foot power pushing a pedal).

Here is the Schematic: (If you want to see a full size image click the image, and then click on the next page image)

Here is a picture of the Joule Thief Generator Circuit as built:(If you want to see a full size image click the image, and then click on the next page image)

And in the following short video of the circuit in operation, I am spinning the stepper at a very slow rate of less than 100RPM and you see the Voltage generated by the stepper never gets above 2VDC, but it is lighting 4 white LEDs in series at about 14VDC: