The first two electromagnets
made were failures. I guess I should have made more
electromagnets when I was a kid.
Both were wound on
a bolt. It seems the diameter of the core affects how strong
the magnet will be.
Wrapping the wire around a NAIL greatly increased the
strength of the magnetic field.
The wire is 26 AWG magnet wire.
The two failed electromagnets
and the good one, (hot glued to the center of the box.) The
failed ones ended up in the recycle bin.
on coil making:
Make two disks of cardboard and put them on the nail. The
nail head holds one disk in position.
Use masking tape to hold the other
disk. Here we are checking for height.
Wind the coil between the disks. This coil was made by
putting the nail in the chuck of a variable speed drill, but
you can wind it by hand. Cut off the end of the nail with a
Use hot glue to hold the wires together, then peel off the
disks and glue it to the center of the cheese box.
Important: the nail must be iron or steel, not
Now is a good time to connect a battery to the coil and make
sure it repels the magnets in the top box. If it attracts,
reverse the battery wires. Mark the positive wire with a
piece of tape for later.
Not a Tip:
Sorry, I have no idea how many turns of wire make up the
coil. It's about 1/3 of an inch in diameter.
on reed switch placement:
After many experiments, a
location for the reed switch was
found. The location is
The switch is not
directly in front of
the electromagnet, but off to the side.
A later version, showing the
The switch works better when in the EDGE of a
magnetic field. Placing the switch directly under the
magnets in the rotating box would result in very poor
Notice the second
(green) switch is larger and has a diode in series with it.
This was one of several experiments.
The switches were burning out after about 20
seconds. I was only using 3 volts, two D cells in
series, and the switches were rated at 90 volts. A
different switch type was purchased (the green ones) but they
continued to burn out. I
had several theories on this.
Theory 1: The
switches, bought on ebay, were Chinese crap. (They
came from China, from a guy named "Jimmy")
Theory 2: The magnets were coming by about 40
times a second (5 revolutions X 8 magnets) and were
too fast for the
switches to handle.
Theory 3: As the magnetic field collapsed it
produced a counter electromotive force in the coil
which could reach over 100 volts.
You could see the
sparking in the switch and hear it as a clicking.
I put a nine
volt battery in the circuit.
The switch burnt out instantly the first time
it was triggered.
Apparently "Theory 3" was the correct one.
The two D
batteries were replaced with a half dead AA
battery. The box rotated perfectly and the switch
didn't burn out.
A homemade battery
holder was made from a piece cut out of a tin can
lid and everything was rather sloppily
glued together with a hot glue gun.
approximate positioning of the
top box with the