> Hello All,
> Yes, I know this is not rocket related but I need to make a big
> electromagnet to pick up nails at our family cabin after our big
> remodeling project these past months. Who better to ask than a bunch of
> wacky rocketeers, right?
> Lots of kids will be running around over the spring and summer so I'd
> like to be safe before we turn them loose to find the nails in their own
> special way. I was thinking of something like a bar or loop wound to
> make a coil and energizing it through a gfi protected 110 circuit. A
> long extension cord and I'd be all set. (this is beginning to sound like
> a "Hey, watch this!" kind of thing) I could also use a big transformer
> (12 volts) or a couple of car batteries if it's nix on the house current
> power supply. Any ideas?
You've seen, I suspect, at least on film, those large electromagnets
that are mounted on cranes to lift car hulks into the crusher (or used
to be -- they seem to mostly use claws now).
Those can lift tonnes.
They run on the equivalent of a couple flashlight batteries.
The strength of the magnet is determined by the product of the number of
turns and the current in the coil. If you keep the current low enough
to avoid burning the thing up (which I watched my dad do with a coil
connected to a car battery when I was about twelve, trying to
remagnetize a really cheap horseshoe magnet needed for a demonstration),
you'll need a lot of wire, and even then you don't need much voltage to
push the current.
For a homemade version, start with a whole spool of "bell wire" (which
you can buy at Radio Shack) -- around 50 m long, with lacquer insulation
to keep the coil compact. Measure the resistance, and then calculate
the current (I = V/R) and power dissipation (P = V^2/R) working from a
single flashlight battery. I think you'll be amazed. Now, if you wind
all that wire onto a compact iron core (like one of those nails, or a
machine***of appropriate length) you'll get the kind of magnet you
want -- assuming it doesn't melt down.
Except that it'll take you well into the '***s (the twenty-***s, that
is) to clean up a yard with a magnet made from a nail with a bunch of
wire wrapped on... B(
Best to rent the commercially made version...
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