How To Build A
Low Tension Coil
For Your
Stationary Engine

This project started off many years ago with the purchase of a roll of magnet wire at a garage sale. As soon as I got home with the wire, I started researching the manufacture of inductors. It turned out that there is a lot to know about coils: there is wire gauge, voltages, amp-turns, air cores, solid cores, laminated cores, pretty oak bases, insulation, tape, shellac, terminals and a myriad of other things that I can't begin to list here.

The amount of information was so great that I realized that there was no hope of designing a proper coil... so the roll of wire sat in a cabinet for years. It sat there until one day I remembered rule number one of old engines: this ain't rocket science and we're not building top fuel funny cars. Accepting rule number one, I gathered up some parts and two hours later had a functional coil.

RAW MATERIALS

The first of the raw materials is the magnet wire. This is the same wire used in motors and transformers. It is copper with a thin layer of insulative coating that must be removed before soldering. The diameter of this wire is 0.054".

"Huh?" you ask, "Why is there beer listed in the raw materials?" Because this is my web page and I SAY we're gonna use beer in making the coil.

You'll just have to trust me on this one. Just remember that this is the 25 ounce can of Fosters, not one of those wimpy twelve ounce cans.

CONSTRUCTION

Part of the problem in building the coil was going to be winding the wire on the core. I don't have a lathe, so I decided to make the core out of a piece of 1/4" pipe. The pipe would fit over a piece of 1/4" rod that would be clamped in the vise. I could then spin the pipe to wind the wire onto it.

The pipe was a couple inches longer than the can. On one end of the pipe was welded a 2.5" washer. Another washer was welded onto the pipe at a distance from the first washer just short of the height of the can (see picture). On the excess end of the pipe was welded a Z shaped crank.

Before winding the wire onto the pipe, it was first wound with friction tape. The tape is necessary to keep the insulation from rubbing on the core, wearing through and causing a short. Leave about six inches of wire on the outside of the coil; attach it to the outside of the washer so it doesn't get tangled when you're winding.

Winding the wire onto the core is not a big deal. Try to keep it relatively even, don't allow kinks and don't scratch it. Now wind, wind, wind; don't stop, keep winding.

After the first five minutes your hand will start to hurt. In a couple more minutes it will start to cramp up. Don't worry, because soon your hand will go numb and it won't hurt any more. That's great, but with a numb hand, it's hard to hold on to a tiny crank. Note to self: next time make crank bigger or get someone else to turn it.

After winding the wire onto the core until it is flush with the washers, take the two wire ends and tape them where they will exit the coil. They should not touch metal at any point. The coil should then be wrapped in cambric or friction tape to protect the wires. The insulation is very thin and delicate.

After taping up the wire, remove the coil from the rod and clamp the excess length of pipe in the vice. Chop it off flush with the washer with a hacksaw. Here is what the finished coil looks like.

It's not very pretty is it? It's hardly anything that you'd want to put next to your beautifully restored engine! Too bad at the beginning of the project we didn't plan for it to be pretty.

But wait! Did we finish that 25 ounce Fosters yet? If not, quit wasting time and get to drinking!

Take the Fosters can and turn it upside down. Now, using your Dremel tool with the cut-off wheel, chop out the bottom of the can. Gingerly place the coil into the can and bring the wires out through the top. Tape well around the opening where the wires come out. You'll need it to be sealed up perfectly.

Now mix up a batch of Kwik-Poly and pour it into the bottom of the Fosters can. (Kwik-Poly is an epoxy product used for sealing gas tanks and you should already have some on hand. If you don't already have some, get some extra for the next time you need to repair a fuel tank. You'll be glad you did.) After filling the can with Kwik-Poly, place the bottom of the can back in place and let the Kwik-Poly set up for five minutes.

You're now done. Hook this baby up to your engine and you're good to go. This coil will put out a good spark on six or twelve volts and will work fine with a small gel-cell.