products offers magneto magnetizer products. About 16% of these are mobile phone bags & cases, 7% are magnetic materials, and 5% are. “Could you send plans and drawings for the magneto charger in your article?” This was the most frequent inquiry I had after my November GEM article on . I would like to build a magnet charger like the one John Rex wrote in the January I have been a full time Magneto Restorer/Repairman for quite a number of.

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This article has drawings and instructions for making and using that charger. Size and expense make the charger most practical for club or group use. The expense can then be divided among the group. Construction of magneto chargers is not a new subject for GEM. Chargers have been described in the following issues: Those units were not sufficiently heavy to charge many magnets while installed on the magneto. Remember that charging the magnets while installed on the magneto is essential.

Chargers with sufficient energy have been pictured in GEM, but no construction details were given. Description The charger described here is designed to operate from a volt automotive battery, has a core area of seven square inches and provides 20, ampere turns of energy. It is sufficient to saturate and charge most fully assembled magnetos used on antique engines. It’s important to state that increasing charger size beyond the point where magnet saturation occurs does not improve magneto performance there’s no harm either.

If you have a source of scrap iron, machine shop facilities and can come up with some surplus magnet wire, the costs can be drastically reduced. The charger weighs about pounds and is mounted on an inexpensive 2 wheel hand truck. This second generation design features ease of construction, improved operation, bottom mounted coil terminals and diode protection to prevent excessive switch sparking and coil failure.

The design The main criteria for any charger design is core area, number of wire turns, and amount of current flowing through the coils. Core area must be large enough to saturate the magneto core without becoming saturated itself. Magnetomotive force product of amps times turns of wire must be large enough to bring magneto magnets to saturation. This charger uses 3-inch diameter soft iron core pieces 6 inches long, each wound with approximately turns of 10 gauge copper magnet wire.

The coils are connected in parallel and protected with diode arc suppressors. A knife switch is used to turn the charger on and off. Materials 2 each 3-inch diameter x 6-inch-long bars C steel for the magnetic coil cores. Miscellaneous equipment, heavy duty solder lugs, 10 gauge hook up wire, solder, other items as required. 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 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 and AB 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. Additional shaped pole pieces are useful for charging flywheels, rotors, etc. The shapes and uses of additional pole pieces have been particularly well described in GEM May-June ’77, pg.

One washer for each coil should be prepared with brass terminal screws as shown. To prevent shorts, the core must be insulated. Cut manila folder into a strip, wind and cement it to the core between insulating maagnetizer.

A half inch overlap prevents any possibility of shorts between the core and wire. The use of magnet wire is important because wire with thick insulation can’t be densely packed. Magnet wire is available from motor rewinding magnetize, transformer shops and suppliers specializing in magnet wire.

The yellow pages of larger mzgnetizer usually list these. Try to purchase two 20 pound rolls rather than one 40 pound roll. The exact number of turns is not important so don’t bother counting turns, just wind until 20 pounds of wire is on each coil.


Wind the coils on a lathe using back gears and clutching. Mount the core with terminal end mqgnetizer the lathe tailstock and run the lathe mahneto reverse to make winding easy to view. This will insure winding direction and poles match those in the photos. Two people are required, one to operate the lathe clutch, while the second layers wire onto the core with gloved hands. If a lathe is not available, coils can be wound by attaching a crank with bolts threaded into each mabneto of the core.

The bolts may be run through wood supports which act as bearings and support the coil during the winding.

The actual winding is started by scraping off a half inch of insulation and poking the wire through the start hole in the insulating end washer and soldering it to a lug on the terminal marked ‘1’. The wire is then wound in layers progressively maneto top of each other. Try to keep the layers uniform with adjacent turns touching tightly.

As winding progresses, it will be more and more difficult to prevent the winding from becoming scrambled. Eventually some scrambling will occur, but try to keep it to a minimum. After most of the 20 pounds is wound, the winding should be planned so the wire will end near the terminal end of the coil.

Guide the wire through the notch on the insulating washer, scrape the insulation off and solder it to a lug at mmagnetizer terminal marked ‘2’.

Tighten a nut and lock washer over each lug. Repeat the procedure for the second coil except mark the terminals ‘3’ and ‘4’ instead of ‘1’ and ‘2’. To magnetizsr the coils from damage, I wound several strips of fiberglass cloth and string over magnero entire coil and painted them with polyester resin. After hardening, the fiberglass and resin were sanded smooth and painted.

At this stage, the coils are finished. Assembly and testing are all that remain. Arc suppressor diodes The purpose of arc suppressor diodes is to reduce the high voltage arc produced by the coils when the switch is opened. This arc is exactly what is wanted across ignitor points with battery and coil ignition, but in a magneto charger, the arc could lead to switch failure, insulation breakdown or electric shock. Diodes absorb the energy when the switch is opened. A second pair of diodes is necessary to prevent magnetizef to the first set in the event the battery is connected backwards.


Alternator diodes will work fine magnfto the ones listed aren’t available. Make sure all diodes are connected exactly as indicated in the wiring diagram note direction maghetizer arrow on diode. Failure to observe this precaution will result in smoked diodes when the charger is powered up! Knife switch The choice of a knife switch has one big advantage.

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You can actually see if it’s open or closed. This is important, because there have been cases where an enclosed switch has had the contacts stick closed even though it indicated open. The result was a set of cooked coils. If an ordinary switch is used, always check the ammeter to make sure the current has stopped flowing when the switch is opened. Ammeter The use of an ammeter, although optional, is useful to monitor the current through the charger.

Once the current has built to a maximum, the switch may be opened because a full charge has been delivered to the magneto magnets. An ordinary automotive ammeter reading 50 amperes is sufficient. The ammeter is connected in series with the switch and mounted to the wood base attached to the hand truck. Fancier ammeters are available from electronic supply houses or surplus electronics stores. The ammeter shown, unlike automotive ammeters, requires the use of an external shunt for operation.

No current will be indicated on the meter if the jumper leads have been improperly connected to the battery. Final assembly Now things start to get heavy, so it’s good to build the charger onto a two wheel hand truck or other cart.

The one pictured has had the joints welded and additional braces welded on to improve strength. The wheels were replaced with old lawn mower wheels which are stronger. The main base is attached to the hand truck using the two pieces of steel angle cut from bed rails. These may be welded or bolted to the hand truck frame.

The coils are now bolted to the base. Other components, such as the knife switch and terminal board, are mounted to a magnetl base on the hand truck. If an ammeter is used, it should be placed away from mangetizer coils so the magnetic field won’t affect mganeto accuracy.

A set of automotive jumper cables attached to the terminal block connects the charger to any 12 volt automotive battery or power source. Testing the charger Once the unit is wired according to the wiring diagram, it’s time to test it.

Connect the leads to a volt automotive battery observing polarity and close the switch. Don’t leave the charger on for more than a few seconds at a time, because the coils and diodes will overheat.

The current should build up to a maximum about 40 amps mwgnetizer about 3 seconds. If not, check the wiring, paying special attention to proper battery polarity and diode polarity. If the wiring and winding have been done as indicated the north and south poles should be as shown in the figures. Mark the poles with the letters N and S to indicate their polarity.