Building a heavy duty magnet charger

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Materials
2 each 3-inch diameter x 6-inch-long bars C-1018 steel for the magnetic coil cores

1 each 3?-inch square x 11-inch long bar C-1018 steel for the base and magnetic return path

4 pieces 1? x 3? x 5 inch rectangular bar C-1018 steel (2 for the pole pieces, 2 for auxiliary pole pieces)

2 each 14-inch long by 1? inch angle iron cut from old bed rails for mounting to hand truck

4 each fiberglass insulating washers 5/16 or ³/₈-inch thick, by 6? inch outside diameter by 3 inch inside diameter for coil end washers (2 have brass bolts for terminals installed)

40 lbs. (two twenty pound rolls if possible) #10 gauge heavy formvar magnet wire for the coils

4 each 22 ampere 50 volt (or greater) diodes, type SK3639 or 5812 for arc suppression (automotive alternator diodes may be used).

10 feet 10 gauge or larger hookup wire for wiring

1 set 12 foot automotive jumper cables at least 8 gauge wire size for lead wires to connect to the automotive battery

2 each ³/₈ x 3? inch bolts to mount coils to magnetic base

2 each ³/₈ x 1? inch socket head cap screws to mount adjustable pole pieces

4 each 5/16 x 1 inch brass flat head bolts for coil terminals

8 each 5/16 inch brass nuts for coil terminals

8 each 5/16 inch lock washers for coil terminals

1 each knife switch (at least 40 amp rated)

1 each terminal block with at least 4 terminals

1 each two wheel hand truck or other cart (optional)

1 each ammeter, 0-50 amp

Miscellaneous equipment, heavy duty solder lugs, 10 gauge hook up wire, solder, other items as required

The magnetic path and pole pieces 
The optimum material for the magnetic path is hydrogen annealed Vanadium Permendur. This material is too high priced so I used low carbon steel. American ingot iron, Swedish charcoal iron, Armco iron, relay iron, and certain low carbon steels are suitable. Do not use tool steels, cast iron or other high carbon steels, they have too much magnetic loss.

I used C-1018 steel for all components in the magnetic path. This is adequate from a magnetic standpoint and is readily available from steel supply yards. The pole pieces are shaped to concentrate the magnetic flux at their tips. An auxiliary set of pole pieces in conjunction with the first set is used in most charging applications and is essential for magnetos such as the Bosch AB-33 and AB-34. To minimize machine work, all material should be sawed to length. The single most important point in machining parts for this charger is to provide close fitting joints at all points in the magnetic path. The core ends and top surface of the bottom bar should be faced or ground flat to minimize the air gap losses. Air is a poor conductor of magnetic flux and we want to put magnetic energy at the pole pieces rather than waste it in cracks and gaps due to poor fits. If a lathe or mill is not available, file and hand scrape the parts for a perfect fit at the joints.

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