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David Kerzel, Pompano Beach, Florida david@FloridaAME.org
Since I was a kid I wanted to build a ignition coil.
I started once with plans from a book but never could get past a few
layers of the very fine secondary windings.
I have been looking at Bob Shores book and thinking about this for several years. I planned to build a coil winder that uses 2 steppers one to wind and one to traverse the wire. A simple program would tie it all together.
A few days ago a thread started about magnetos and I got thinking about them again. The first part of a magneto is a good ignition coil. Then use a permanent magnet for the magnetic field rather than a battery.
I started with a 20 VA Signal transformer for the core of silicon iron.
I hack sawed the send off and milled it flat. A few layers were separated to end up with a core 3/8 square and 1.9 long. I insulated it with polyester tape (Scotch Magic tape)
Each layer is 70 turns of #26 wire.
3 layers for a total of 210 turns in the primary. A little super glue to hold things in place and a outer layer of polyester tape.
I made a winding fixture. A ball bearing shaft to support the roll of wire. Part of a Sherline index moves the wire guide. A stepper motor drives the bobbin using a simple driver circuit. The computer controls that steps and counts them out.
There is a lot of this #44 wire on a 10 LB roll, nearly 200 miles. The wire is 0.0025 inches in diameter and not very strong.
My coil design has a number of narrow windings separated by Teflon fins. The slots are .040 wide and about .018 deep. and hold 1000 turns. It started real good then the wire snapped in segment 2. From then on I could not get more than 50 turns. Something was wrong on the roll.
I figured if I could get a layer off it might start to unwind normally again. Hours later I gave up and will look for some new wire this week.
I got a new roll of wire 1.6Lb this time (the first roll was 10 Lb)
and paid more, but it un spooled perfectly.
Next I need to add some leads and mate the secondary with the primary. Then I will first test it with a spark gap and if it works go to a engine.
The coil is together and has a transistor driver (IGBT) that simulates engine operation with a 60 degree dwell. Sparks are intense and have a loud report. The largest gap I have tried was 3/8 inch and it worked fine. After several hours of operation the core has heated. I suspect it needs to be a little longer for more cooling area. I am pleased with the operation so far and hope to get a on engine test soon.
As a project this one took a lot of time and was expensive for the end product. I enjoyed it and have another long term project done and off the list.
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