antenna-theory.com

[Donny Bahama]

I hope it's OK to post this here; it's not antenna related (I was directed here from the Maxwells-Equations site) but there doesn't seem to be any 'other topics' forum. If this post is deemed inappropriate, I do apologize.

I want to create a circuit in which a hand crank charges up one or more batteries or capacitors, which in turn discharge slowly through an electromagnetic coil (such that the magnetic field of the electromagnet gradually diminishes) over the course of an hour or so.

The overall idea is that you crank the crank for a short while, creating a magnetic field so that BBs cling to the electromagnet. But little by little, over the course of maybe 20 or 30 minutes (longer would be OK), the BBs drop off one by one (or a few at a time).

What would such a circuit look like? What variables will determine how long the crank has to be turned, how strong the magnetic field will be and how slowly it will discharge? And will the BBs only cling to the ends of the electromagnet? Or will they cling along the length of it as well? (I'll need a fairly large surface area - maybe more than one.

My initial thought was that the magnet would be at the top and the BBs would cling from the bottom of the magnet until the magnetic field dissipated enough for them to fall, but now I'm thinking of having the BBs rest on top of the magnet which would be placed at a slight angle so the BBs can just roll off as the magnetic field dissipates. I would assume that this would require less of a charge and less cranking.

Thanks very much for your time and consideration!

[bigSteve]

It's fine to post here. Some notes:

- you need d.c. current to flow in a loop to make an electromagnet
- you won't have anything of an electromagnet unless you have a bunch of loops of wire around iron. you must have iron! no steel

Do some research to figure out what current you need - take a battery (D-cell) around an iron nail, figure out the current flow by putting a resistor in series, and see what you need to generate.

To get your hand crank voltage, just figure out how those hand cranked voltage gneerators work, or buy one, and copy it.

Make sense?