I played with something like this in my youth. If it is only being used by
the person who built it, and if this person is careful and uses an earth
leakage breaker (residual current circuit breaker) then just make sure that
the connections are mechanically secure and insulated with a couple of
layers of insulating tape, heatshrink etc. Obviously don't use it with wet
hands etc. etc. standard disclaimers etc. and of course it shouldn't be
left unattended like that blah blah don't sue blah. I used just a plastic
shrouded terminal block, and that was on 240V. I put tape over all exposed
windings to protect the insulation from scratches. I was fairly careful
because I already knew what 240V feels like. I guess I was about 10 years
old, and I spent weeks playing with that thing and didn't get any shocks,
until I stupidly held an old relay coil near it, which formed a secondary
winding and in a fraction if a second it burnt right through the skin of my
thumb where the relay coil terminals happened to be, i.e. the only thing I
got a shock from was not even connected to the mains (line voltage) at all!
I certainly learnt about electromagnetic induction and the smell of burning
thumb.
#15 magnet wire is about 3.2 ohms per 1000 feet. If your tube was 3"
diameter, then you have about 300 or so feet of wire, and about an ohm
of resistance. Hooking this straight to 120VAC will suck 120Amps
through it, and this is not a Good Thing.
Not if it has an iron core - this is AC not DC, and inductance has an
effect. Learning about that is a good reason to do this experiment. The
coil I used was would on a spool with perhaps 40mm inside diameter and
120mm outside diameter and the length of the coil former was about 120mm.
The wire was about 1.7mm diameter enamelled winding wire and the spool was
wound full of wire. Inside the former was a loose fitting PVC pipe about
500mm long and the right diameter to fill up the hole in the coil, i.e.
around 40mm. The pipe could be inserted and removed from the coil as
necessary. I packed the PVC pipe full of soft iron welding rods (for
oxy-acetylene welding, not flux coated). I used it on 240VAC for up to
about 1 second, it probably drew 10-15 Amps. It could fire a piece of
copper pipe with enough force to be painful if stopped by the palm of your
hand and dangerous if it hit a person on the head etc.
Probably more interesting was the use of this coil attached to a variac
(variable autotransformer) or a 120V stepdown transformer. You could heat
metal rings past the melting point of solder and light an automotive light
bulb by wrapping a few turns around the iron core. If you tried to pull
the core out of the coil, the fuse would blow because the inductance of the
coil would be reduced without the core.
You will trip breakers etc,
and 120 Amps is very close to the fusing current of #15 wire (meaning
the coil will open up when a section turns into a puff of hot molten
copper nearly instantly).
I found that the fuse invariably blew before the coil, though slow
overheating of the coil was a bigger problem, which necessitated 1/2 hour
cooling off periods which I found very tedious.
I suspect you want to run your coil off of a 12V or 24V power supply.
At 12V you need 12 Amps, at 24V you need 24 Amps. This last current
will get the wire decently warm but will not get anywhere near melting
it.
Really you need at least 1kVA before the coil is much fun to play with,
IMHO.
[...]
I think the traditional physics-class-demo electromagnet has a current
more like 10 or 15 amps go through it when hooked to 120VAC (via a
pretty hefty pushbutton usually, sometimes they use a contactor rated
at this current and use low voltage DC to control the contactor).
Yes that's more like it...
You'd need 10 times as many turns to get to this resistance (again
depends on your tube diameter),
But you can get enough inductance easily with a bunch of welding rods.
I think these coils are usually wound
with 18 or 20AWG wire (you get more resistance per turn and it's not
completely dangerous to put 15 amps through these wires for very brief
periods.)
Tim.
You probably could benefit from even fatter wire and less turns than I used
if you only have puny little wussy 120V power. Anyway have fun and be
careful.
Chris
