Magneto Recharging

Pages From the Past - Tips for Antique Engine Magnetos

| April/May 2011

“How often do magnetos need recharging?” is a question frequently asked by antique engine enthusiasts. The answer has to do with the permanence of the magnet on the engine magneto.

It is a common fallacy that a permanent magnet expends internal energy to create electricity from an engine magneto or generator. This fallacy leads to the belief that after repeated use the magnetism will all be used up and hence the magnet must be recharged. The energy to create the spark comes not from the magnet, but from the mechanical energy required to drive the engine magneto. The magnet merely acts to convert this mechanical energy to electrical energy.

Owners of antique engines sometimes report that their magneto has mysteriously lost its magnetism. In most cases, the fact that the magnetism has been lost cannot be questioned; however, the “mysterious” aspect can be disputed. There is nothing mysterious about it. If a piece of material can be magnetized, it is likewise capable of being demagnetized.

Magneto recharging tips 

• Take the case of an engine enthusiast who wants to get the maximum performance out of his engine magneto. He removes the magnets, takes them to his local magneto service center for recharging, then puts them back on the mag. Now he gets a weaker spark than before. Why? Because removing the magnets subjects them to demagnetizing forces, the recharging restored the magnetism, but they again lost some of their magnetism upon removal from the charger. What’s the right way to recharge them? Charge them on the magneto as an assembly. Removing the magnets from a magneto causes them to lose some of their magnetism.

• Don’t pile several magnetos together in a heap or pile. Having magnets close together can cause them to partially demagnetize each other. Keep magnetos away from each other by at least 3 inches.