Building Magnet Chargers

| March/April 2002

Magneto Charger

Harry Matthew's Weidenhoff magneto charger.

The following comes from a recent topic on SmokStak, which can be found on the Internet at: smokstak.cgi. As ever, various individuals started, commented on and concluded the following bulletin board thread.

I would like to build a magnet charger like the one John Rex wrote up in the January 1989 GEM (see Gas Engine Magazine, January 1989, page 22, 'Building a Heavy Duty Magneto Charger'). I've wanted to do this for years, but never could find a source for the wire needed. It takes 40-lbs (preferably two 20-lb rolls) of 10-gauge, heavy Formvar magnet wire. Where can the average man find some of this? Also, a good, heavy, 40-amp knife switch? I like this style charger because, as Rex states, it will saturate any magnet without removing the magnet from the rest of the assembly. - Jim

I made a charger like the one you're building. I got the wire from a place that rebuilt industrial electric motors. Told them exactly what I needed and they came up with two spools at a very good price. As for the switch, poke about in old city electric buildings or factory electrical rooms. My switch came from the electric distribution room of a local manufacturing company. They were ripping all the stuff out and tossing it in a dumpster. Traded a dozen donuts to the wrecking crew for the switch. - Nick

I recently built a charger to Dave Gingery's plan. Simple and easy to build, 115-volt converted to DC with a $5.95 bridge rectifier, two spools of 6-lb, 18-gauge magnet wire from motor rewinders. It's safe, draws 8 amps, weighs approx 50-lbs finished, and with a bar across the poles when engaged lifts it right off the bench! It can charge most mags without dismantling. The total cost was $48, having had the two-inch steel cores in my scrap pile. - Fenwood

Hi Folks, this is not meant to be rain on anyone's parade, but I feel it is necessary to point out a small fact about magnet chargers. I have been a full-time magneto restorer/repairman for a number of years, and have owned a number of original magnet chargers built by some of the leading names in magnetos. These were built by the manufacturers and intended for use by their own 'Factory Authorized' service outlets. Without exception they have all been LARGE, HEAVY pieces of equipment. The American Bosch unit that sets on my bench weighs 240 pounds. I am of the opinion that if F-M, American Bosch and IHC thought a 25-lb charger would do an adequate job, that is what they would have built.

I am sure that if all you want to do is punch up the charge on your own mags a little the $50 to $100 units will at least not do any harm. But if you are truly looking to have a real magnet charger, take a long, hard look at the one that John Rex designed. Please don't just take my word for it. Ask any of the many mag guys that are in this hobby. - Ted Two things go into design of an electromagnet; the number of amp-turns (AT) and the magnetic permeability of the pole pieces. That will determine the maximum field you can generate to charge magnets. The AT is just the number of amps flowing through the coil of 'n' turns (have to divide by the area of the pole pieces.) Having a large pole to charge a wide variety of magnets means you'll need a 'Rex' type charger with many turns carrying high current.