A solenoid from a vehicle might work well. The best wire for practical
use would be copper, and it must be insulated to avoid shorts.
As for the battery charger, you have to be very careful not to run
too much current through the coil, because it will get very hot and
might catch fire. Or your battery charger could respond badly to being
short-circuited like that and catch fire or just stop working. Try
running small currents first- maybe from a low-voltage battery- and see
how hot the coil gets after a while (or how dead your batter gets).
Then build up. Perhaps a vehicle solenoid will be designed to work well
at 12 V, which would match the standard charger, but I'm not sure how
long you can run the solenoid at that voltage before it fries- maybe
starting a fire. Maybe a 6V charger will work ok with a solenoid
designed for short-term 12V use. Anyway, be very careful about
You can limit the current going through the magnet with a (small)
resistance in series. If the solenoid has negligible resistance itself,
then putting an ideal external voltage source across its leads will
lead to current which increases forever (until something gives out).
Resistance will keep the current limited.
One issue is always turning off a solenoid with current in it. If
the solenoid has lots of inductance and is runnning with a large
current, it has lots of stored energy. Removing the leads quickly when
a lot of energy is stored in the solenoid will cause this energy to be
dissipated in a big spark where the lead is separated. Be careful!
(republished on 08/02/06)