Information on Sparking Coils & Magnet Chargers

Information on how to make a sparking coil and a magnet charger

| January/February 1984

  • Construction of low-tension sparking coil
    Construction of low-tension sparking coil.
  • Magnet Recharger
    Design for magnet recharger.
    Courtesy of "The Horseless Age"
  • Magnet Recharger
    Diagram of connection of magnet recharger.
    Courtesy of "The Horseless Age"

  • Construction of low-tension sparking coil
  • Magnet Recharger
  • Magnet Recharger


A simple primary sparking coil may be made with a core of iron (no. 16) ten inches long and one inch in diameter. Fasten heads for the spool on this, and cover the core with a few turns of brown paper shellacked to make a tube. Wind No. 14 single cotton-covered magnet wire on this to a depth of about 5/8-inch, insulating each layer from the next by a layer of paper. Give each layer a coat of shellac also. The coil is used in series with a battery, and the spark is obtained when the circuit is broken. With six or eight strong cells a thick spark will be given. This sparking coil is illustrated. Make at least eight windings. This spark coil is the result of large experience in an effort to produce the largest spark from the least battery current. Its short length and large number of wire turns make the magnetic changes instantaneous, producing a hot and powerful spark, so necessary in old engines.


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 x 1 x 5/8 inches and are provided with pole pieces measuring 1 x 1 x 5/8 inches. All contacting surfaces should be absolutely flat and square so that there will be good metallic 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 recharge 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 flamable 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. Remagnetizing 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 to 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 side-ways from the recharger. The keeper should remain in place until the magnet is reassembled on the magneto. Good luck.

Jack comments: "I have found that a lot of people in the engine hobby have trouble with magnetos. They just don't seem to work. Most magnetos have sat on the shelf for years and weren't used. The magnets will not hold their charge forever. In almost all cases all that is needed to get it operational again is to give it a good cleaning, and recharge the magnets. A good magneto repair will do this for you, but will take about $50 or $75 out of your pocket. This charger will work on all types of magnets and do a good job. The only magnetos that I have found don't work too well even after charging are the Bosch AB 33 and AB 34. I don't think that these two magnetos were very good when they were new. If anyone out there has any questions, feel free to drop me a line and we'll help all we can."

Jack Versteeg, president of the Early Day Gas Engine & Tractor Association, has provided two very helpful articles which we present together in this issue. We seek all kinds of authoritative articles on the technical aspects of restoring and collecting, and will be glad to hear from you if you feel you can add to others' store of knowledge. If you wish to write to Jack direct about his information, or to inquire about the EDGE&TA, his address is 1215 Jays Drive, N.E., Salem, OR 97303. 


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