This week, I wound a new secondary coil for my million volt Tesla coil. This is part of a redesign project, aimed at making it easier to set up and tear down for shows. I always find winding coils very soothing, so I thought that I would select an experiment where you could try winding a coil yourself. You will need:
- six or seven feet of insulated wire
- an iron or steel bolt, about 4 inches long
- a nine volt battery
- some paperclips
First, lets test to see if the bolt is already magnetized. Lay several paper clips on a flat surface and touch them with the bolt. Move the bolt around and watch to see if the paper clips stick to it. Unless your bolt is already a magnet, they won't.
Cut a piece of wire about 6 or 7 feet long. You can get 22 gauge hookup wire at Radio Shack or similar wire from your hardware store. Carefully remove about an inch of the plastic insulation from each end. Measure about six inches from one end of the wire and tie the wire about the bolt. Slide the wire to the end of the bolt and begin winding the wire around the bolt. Go slowly, trying to wind the wire in a single layer, with the turns close together, to make a smooth coil. Keep winding until you reach the other end of the bolt, or until you only have about 6 inches of wire left. Wrap the coil with tape, so it will not unwind. You may have some wire left over when you get to the end of the bolt. That is OK.
Next, attach the ends of the wire to the terminals on the battery. In the U.S., nine volt batteries are small and have two small, round terminals on the top. By bending the wire into a hook shape, you can wrap one wire around each terminal and use a little tape to hold it in place. Do not use a large battery, as this can cause the wire to get very hot.
Once you connect the wire, test the bolt with the paper clips again. This time, you should find that the paper clips tend to stick to the bolt. If not, check to see that you have a good connection between the wires and the battery, and that the battery is fresh and strong. Remove the wire from the battery and the electromagnet will turn off, although the bolt may stay slightly magnetized for a minute.
Why does the bolt become a magnet? When electricity flows through a wire, it produces a magnetic field. For a straight wire, this field is usually not very strong, but by winding the wire into a coil, you make the field stronger. This field causes the magnetic domains in the bolt to line up, forming a fairly strong magnet.
How strong your magnet will be depends on several things. The more times you wind the wire around the bolt, the stronger your magnet will be. If you have extra wire left over, you might try wrapping a second layer of turns on your bolt. Be sure that all of the wire is wound in the same direction, or you will make the magnet weaker instead of stronger. You can also make your magnet stronger by winding the coil very smoothly, making sure that the wires all line up side by side. Using a fresh, strong battery gives you a stronger magnet than a battery that has been used.
WARNING! Do not connect your electromagnet to the electricity from a household outlet. The electricity in the outlets of your home contains far too much electricity and can cause the coil to catch on fire, as well as giving you a very dangerous shock. Also, the coil may get hot if you leave it connected to the battery too long. When you are done testing, disconnect the battery.