Make Your Own Magnet Charger

You can charge it!

| December/January 2010

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    Peter Rooke recharges a Webster magneto on his homemade magnet charger. Note the use of the blocks to get good connection with the magnets. 
    Photo by Peter Rooke
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    Turning the skin off the core.
    Photo by Peter Rooke
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    Skimming the top face before turning the lip to hold the upper insulation ring. 
    Photo by Peter Rooke
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    Flycutting the top of the base plate. 
    Photo by Peter Rooke
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    A bottom insulating ring, showing the groove cut for the wire.
    Photo by Peter Rooke
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    The first layer wound on the core. 
    Photo by Peter Rooke
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    The winding setup for the coils, using the lathe. The card insulation on the core can be seen. 
    Photo by Peter Rooke
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    The bottom of the core after placing on the surface plate. 
    Photo by Peter Rooke
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    The wound core. The bolt in the top was temporary, being center drilled and used to protect the thread when using the lathe center.
    Photo by Peter Rooke
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    Soldering the hook up wire to the end of the winding wire. The epoxy coating of the core can be seen.
    Photo by Peter Rooke
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    Covering the epoxy with tape, the joint with the hook up wire, covered with heat shrink, can be seen.
    Photo by Peter Rooke
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    Terminals for the alligator clips for the battery leads.
    Photo by Peter Rooke
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    Wiring inside of the box. The ammeter has been fixed to the inside of the lid at top.
    Photo by Peter Rooke
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    Wiring diagram.
    Photo by Peter Rooke
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    Completed charger without pole pieces. The red paint marking the positive terminal is visible as are the clear markings of the north and south poles.
    Photo by Peter Rooke
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    An IHC Model L magneto being charged.
    Photo by Peter Rooke

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Part 1 described the thought processes leading to the design of a charger and the preparation of the plans. Next the enjoyable part: machining metal.

My usual supplier of steel was able to source some “black steel,” which is similar to C1018 in that it has less than 0.2 percent carbon content. In reality this has properties similar to iron, although is not as good as pure magnet iron. Round black steel has a rough surface, so it needs to be ordered oversize so that it can be machined to a good finish.

I ordered a 12-inch length of 3.5-inch diameter steel together with a 12-inch length of 4-by-2.5-inch steel that would be used for the base. In addition an 18-inch length of 3.5-by-1.5-inch steel was ordered to cut up and machine to provide four pole pieces.

While 200 turns of 10 AWG wire per coil would in theory have generated near 45,000 ampere-turns, the current drawn would be high at over 100 amps. This could be reduced to 74 amps by increasing the number of turns to 300, still achieving the same number of amp-turns. In addition, a standard 4-kg coil from the supplier held just sufficient to wind 300 turns (if the starting diameter of the core is 3 inches). Furthermore, winding 3-inch diameter for 5 inches of the core results in the winding being nearly 6 layers, which meant it could start and finish near the bottom. The copper wire ordered was class H winding wire, with a dual polyester coating capable of withstanding high abrasion and temperatures.



Some hard plastic, acquired many years ago and since stored in a corner of the workshop, was used to form the end plates and the platform to rest the magneto on while it was charged.
To help reduce arcing when the power was switched on and off, a 12-volt car starter solenoid was purchased, along with a simple press switch, some connecting wire (6 and 8 AWG) and terminal screws. There will still be some arcing of these points so rectifier diodes were needed to suppress it.

For a more professional device an ammeter can be added, which is very useful since it shows when peak amperes are flowing. This allows for the power to be switched off one second later, by which time the cores of the coils would be fully saturated.