The following includes tips on how to build and use a homemade magneto magnet charger.
The cores of the electromagnet are made of soft bar steel one inch in diameter and three inches long. They are secured to a steel base measuring 5-1/4 by 1-1/2 by 5/8 inch and are provided with pole pieces measuring 1-3/4 x 1-3/4 by 5/8 inch. All contacting surfaces should be absolutely flat and square so that there will be good metalic contact over the entire surfaces. Before the wire is wound on them, the magnet cores must be insulated. A spool may be formed by placing fiber or cardboard washers around each end of the magnet cores and then wrapping the magnet cores themselves with several layers of electricians tape. The winding for this recharger is for use on 6 or 12 volt direct current, from automobile storage batteries. Applying three layers of No. 12 double cotton covered magnet wire is preferred. However, No. 12 gauge copper thermoplastic covered type "TW" house and building wire will give satisfactory service and results. Wind the wire around the electromagnet cores as shown in the illustrations and then wrap tape around the windings, to hold them in place. Mount the recharger on a wooden base large enough to also hold a single pole switch and a binding post.
CAUTION, the switch is a must, as the recharger draws high amperage from the battery. As a result, the battery has a tendency to produce some flammable gas, and any sparks around the battery vents could cause a fire and/or an explosion. Therefore, do not connect or disconnect the lead wires from the battery when the recharger is turned on. The windings will heat up quickly when in use; therefore, the switch should be closed for only a few minutes at a time. When a magneto is taken apart for any reason, it must be assembled with the magnets in the same relative position as formerly, otherwise their polarity may be reversed and the magneto will be inoperative. The magnets must never be left off the magneto even temporarily, without placing a steel bar across their poles to serve as a keeper. Unless this is done, they will lose their magnetism rapidly. Re-magnetizing the magnets of a magneto that has become weakened through long use is a simple process.
It is important that unlike poles of the magneto magnets and of the electro magnets be brought together; i.e. the North pole of the magneto magnet to the South pole of the electromagnet and vice versa. To insure this, the current should be turned into the electromagnet and magneto magnet suspended over it on a string. Starting at a distance of about 12 inches, slowly lower the magneto magnet. As you begin to lower the magneto magnet towards the electromagnet, the magneto magnet will automatically seek the proper polarity by swinging around and will then be strongly attracted to the electromagnet.
In recharging, set the magnet on top of the recharger after its polarity has been determined, and rock the magnet back and forth on its pole edges a number of times. Then lay it on its side with its poles away from you and extending just beyond the far edges of the electromagnet poles. Apply a keeper to the magnet poles, switch off the current and withdraw the magnet sideways from the recharger. The keeper should remain in place until the magnet is reassembled on the magneto.