using a coil and magnet to power an LED

Ummm Err... Ahhhh Is this a trick question??? Really, the LED, coil and moving magnet are the only things you need, if the magnet is strong enough and the coil is large enough and the movement is fast enough. Can you elaborate a bit more on the specifics of your project, or is it classified?

"Mike Pinch" schreef in bericht news:AvCdnb0zDJyJsJ_ZnZ2dnUVZ snipped-for-privacy@comcast.com...

I would try a coil and a moving magnet.

Hi Mike, I'm sure you have seen the flashlights that you shake back and forth, causing a magnet to slide inside of a coil. These flashlights store the charge in a capacitor while your not shaking it. Is this the idea your after? Would a rotating coil and a stationary magnet work for you? Go to Radio Shack and get a small DC motor, connect the LED to the motor with the correct polarity and then spin the motor, the LED should glow. Give us a better idea of what your after. Mike

or a moving coil amd a magnet?

seems to work in LTspice

martin

Wind a couple/few hundred turns of small-gauge wire around maybe a toilet-paper cardboard core. Use maybe #30 enameled magnet wire. Connect it to the led or preferably to a pair of leds connected anti-parallel.

Drop a super-magnet, like one of the rare-earth things from an old hard drive, through the hole, the faster the better. The led's should flash.

More fun: drop a supermagnet straight down inside a long hunk of 3/4 inch copper water pipe. Release it and quickly look down the pipe as it drops.

I recently tried dropping a quarter down the bore of a megabuck superconductive magnet, expecting the eddy currents to slow its fall. It never came out the bottom, not because of the field but because it jammed in a flange halfway down. Very embarassing.

John

"martin griffith" schreef in bericht news: snipped-for-privacy@4ax.com...

an

Yabbut, the OP is not interested in that.

I bet ;)

You win,I lied. I couldn't find a symbol for a hand waving a coil (or magnet)

martin

"martin griffith" a écrit dans le message de news: snipped-for-privacy@4ax.com...

up

Did you put that nice zero threshold bridge, so that it lights whatever the direction you move the magnet.

And with a transformer, if you suffer from Parkinson's disease you could make yourself a powerless christmas tree.

Take the guts out of this:

and you have what you need. Moving magnet, coil, LED, let there be - shake shake shake - light!

No. You just model the coil and magnet in spice and then pick up the PC and shake in back and forth, just like one of those flashlights.

Don't forget the bridge rectifier and the supercap.

-- Paul Hovnanian mailto: snipped-for-privacy@Hovnanian.com

------------------------------------------------------------------ Disclaimer - These opiini^H^H damn! ^H^H ^Q ^[ .... :w :q :wq :wq! ^d exit X Q ^C ^? :quitbye CtrlAltDel ~~q :~q logout save/quit :!QUIT ^[zz ^[ZZZZZZ ^H man vi ^@ ^L ^[c ^# ^E ^X ^I ^T ? help helpquit ^D man quit ^C ^c ?Quit ?q CtrlShftDel "Hey, what does this button d..."

Elegant! I would add a LED to that.

Ed

I just got back. Thanks for the feedback.

The application isn't really classified in the sense that I'm not planning on putting LEDs into a stronglink or anything but there are some geometrical constraints which will mostly impact the coil. Any standard LED will fit into the space I have. The intent is to have the LED flash briefly but intensely. The coil needs to fit in a fairly narrow space so it needs to be "flat" (as in probably occupying less than 1/4 inch thickness) . The coil can be long. Let's say we had a long thin coil with lots of windings.

If there is a long slender coil (say 4 inches long wrapped around an 1/8" diameter mandrel) with the proper number of turns, does the influence of the magnet (which is let's say 1/4" diameter x 1/10" thick) become time-dependent? Will the induced current gradually build up as this magnet traverses along the coil? Are additional components needed in this case? Remember, I am looking for a briefly flashing LED -- no constant output required.

Also, I am messing around with various coils, chokes and wal-warts. Some of these devices seem to have a metal mandrel, some don't. How do I know what kind of mandrel (core) to use?

Regards,

Mike

Hello Michael,

Just when I thought I had it you changed rules.

Actually one method is using three small button type batteries and a super bright LED. Make certain the LED forward voltage is under 4 volts. Kids tennis shoes use this method. Look around in the toy section Walmart, I found packs of three 1" plastic marbles for $3 with a built in flashing IC chip, circuit board, four colors super brite LED's and the three batteries. That's for each marble!

This triggers from a small spring switch that senses a mild impact.

Trying to achieve 4 volts off of a very small coil and magnet seems a bit challenging.

I don't think you mentioned what triggers your LED, physical motion?

• * * Christopher

Temecula CA.USA

Christopher,

Excellent feedback; thanks.

I didn't want to use batteries in this application. The application is such that human intervention to change batteries is undesirable.

Here's a question -- does a coil necessarily need to be wound in a circular fashion (cross section) or could a coil be wrapped around say a flat piece of something (like a popsicle stick)?

Mike

Like this ?

Graham

Our 20 month old has sneakers with a couple of LEDs on them that flash when she walks. I assume there is a coil with a loose fitting magnet in the shoes. Let me see if the wife kept the older too small ones, and I'll cut them open to see what's inside...

Lukas

A battery...