Author Options:

is there an easy way to measure the weber stength of a magnet? Answered

Have been given the task of creating a circuit powered by a rotating magnet in a copper coil that will charge a capacitor long enough to light an LED for 600 seconds after the rotating magnet has stopped.

In all the magnet charge up torches I've opened, there are two 3V Lithium Cells (CR 2032) between the generator and the circuit. These cells aren't rechargable. The current from the generator is AC.

I know this shouldn't be too difficult, but can't figure out how to approach it with so many unknown variables. Just looking for any help possible for value of capacitor or resistor.

Thanks for any help!



10 years ago

I've not taken apart any of these torches yet but I can make some assumptions.

The do generate a/c so to charge a battery it has to be rectified intodc to charge a battery.  I believe that that is done by theLED.  After all it is a diode.  I haven't tried it yet but itshould work.  Either that or there is another diode somewhere inthe circuit.

Either the Cells are rechargeable or there is something else there thatyou're missing.  I don't know what they would be for unless theyare rechargeable.

In your case though for what you are trying to accomplish you need themagnet, a coil and some way to support and rotate the magnet.  Youneed a diode to rectify the current a switch to change the circuit fromcharging to lighting.  You want to disconnect the light from thecircuit until you are ready to time the light.  You may be able touse the led as the rectifier.  I'm not at my shop to test this.

And you need a capacitor to be charged.  I have no idea what sizecapacitor you need.  Start with something small and get the systemworking so that you know you are acutally storing voltage in thecap.  Then work up to something bigger.

Is there any limit on how long you can generate before you start thetimed trial?
And how are you actually going rotate the magnet?

And as always, take good photos and notes and make an instructable outof this.


Answer 10 years ago

If you use just a diode you are wasting half of your effort. Use a <a href="http://en.wikipedia.org/wiki/Diode_bridge">diode bridge like this</a> and you'll use more of the energy.<br />


10 years ago

does the light have to go out when it have been 600 seconds?