Design Your Own Magnet Charger

You can charge it!

| September 2009

This is Part 1 of a 2 part series. This article describes the development of Peter Rooke's homemade charger design and the preparation of the plans. Part 2 describes the machining of the magnet charger.

While a friend of mine had a magnet charger, I always felt a little uneasy about putting him to the trouble of ensuring that the battery that powered it was fully charged and the fact he had to clear his work bench to make room to use it.

Part of the satisfaction I gain from restoring engines arises from the turning of various bits of metal into a working piece of machinery, so I felt that to make a charger would be a new challenge, and that I would also learn something in the process. I knew little about electricity, apart from being able to change a plug, and knew even less about magnetism. Fortunately, I still met my old school physics teacher for a glass of beer most weeks, as we were both members of a local rifle club, more social members now with failing eyesight! However my hopes of an immediate flow of information just elicited the initial comment “yes, magnetism – a tricky subject,” and he started to talk about something else!

Next, I searched and a few hours were well spent gathering numerous comments as well as print outs of articles detailing plans to build magnetizers, including a comprehensive one by John Rex printed in the January/February 1989 issue of Gas Engine Magazine, and a copy of an article in Dyke’s Automobile and Gasoline Engine Encyclopaedia in 1918. There was also reference to a Dave Gingery design.

This was fine but I was no further along as I now had three schemes, each one using different size cores, all of which were, according to numerous people, successful. The only common point that I was able to identify was that 20,000 ampere-turns of copper wire appeared to be the magic number to achieve the full charging of a magneto. Ampere-turns refer to the number of turns of wire around the core multiplied by the amperes that the length of wire draws.

The first decision was to identify the optimum core size before calculating the gauge and amount of wire to wind around this, along with the power source to achieve the desired result.