Stepper Motor Generator

[High4Volts]

I found (3) 1.45VDC Synchronous Stepping Motors at work in teh trash. I can spin all three by hand and they produce up to 15V on a meter maybe more if i spin them faster. My question is what kind of generator could these be used for? They are rated at 15.2 amps. 200 steps/revolution. There is no RPM rating on the plate.

[bodgy]

A UK electronics magazine (EPE) used something similar in their version of a 'Bayliss' wind up torch last year.<p>The Author was Rev. T Scarborough.<p>
Colin

[jollyrgr]

If you get the magazine there is an article in the November 2003 (current) issue that covers the steps needed to convert a stepper motor into a generator. See the article about the Wind Up Flashlight on page 40. And it is by Thomas Scarborough, the same author as the article bodgy mentions. Should you not get the magazine, I will give you a short summary of the generator portion of the circuit. It is not that difficult. The stepper motor is basically converted into an alternator with external rectification.<p>Simple conversion steps.<p>Find the COMMON lead. This is easy if the motor is labeled. Since you seem to have already been able to measure the voltage you probably have this step covered already.<p>Depending on how many windings these motors have you will want to get an equal number of full wave bridge rectifiers. <p>Tie one of the AC inputs from each of the bridge rectifiers to the common lead of the stepper. <p>Connect the other end of each winding to ONE of the bridge rectifiers AC leads.<p>Connect all of the + outputs from all the bridge rectifiers together. Connect all of the - outputs from all of the bridge rectifiers together.<p>Place a large electrolytic capacitor across the + and - leads observing proper polarity. Make sure the voltage rating of the capacitor is above that of the stepper motor by several volts.<p>If you want you could also simply use a SINGLE diode at each of the winding leads and make the COMMON your ground point. <p>(In case anyone cares, this is pretty much what a standard car alternator is all about except there are three rectifiers (called a DIODE TRIO) usually in a single four lead device. The three windings have a single common grounded to the alternator frame. The individual output coils go to their own diode in the diode trio. The three diodes are tied to a common point inside the rectifier device which then goes to a solid state regulator input. The output of the regulator is the output of the alternator. This is a little more simplistic but is the basic idea.) <p>In summary here is what you have done.<p>Connected one AC input lead from each of the bridge rectifiers to the COMMON lead of the motor. So if you have six windings on the stepper you should have six bridge rectifiers with one of the AC leads from each connected to the common.<p>Each of the remaining coils/leads of the stepper goes to its own bridge rectifier AC input.<p>Next you have tied all of the + (Positive) terminals of the six bridge rectifiers together at one node. You also tie all of the - (Negative) terminals of the bridge rectifiers together at one node. This leaves you with a single positive connection and a negative connection.<p>Across the + and - connections you have added a large (in farads) capacitor to store the energy generated.<p>Now you can add a hand crank and use this to generate "free" power. This free power could be used to charge your cell phone battery, power a flashlight (as in the Scarborough article), or whatever you wanted to do with it.<p>The Scarborough article was a good idea but in my opinion he missed an important consideration. With his version one must constantly turn the handle to get light. If the voltage were lowered (regulated) and five volts was dumped into a 5.5 volt, one farad memory capacitor (or "GOLDCAP" if you will) one could crank for about thirty seconds and get about five minutes of light. Yes it might be dimmer but then you don't have to constantly crank the device to get light. He does mention using "goldcaps" in the sidebar but this should have been the goal from the start.

[Johnm48]

Has any one got a source for the MAX 639? A quantity of two would be good, I have found a
source for minimum of 100. But I’m not building that many lights.

[bodgy]

You can buy them direct from Maxim <p>www.maxim-ic.com<p>While you are on the site an alternative may spring to mind.<p>Colin