Based on a design dating from the
1920s
To build one you will need access to a lathe.
13" of soft iron bar 1.25"dia .
Insulated wire lots of it.
Insulating tape etc.
The wire that I used I picked up from a guy at an auto
jumble for five pounds. The wire is lacquered 2mm diameter and weighed
about 6 Kilo.
The soft iron cores I used were just over 1" diameter and 6" long. The last half inch was turned down to a smaller diameter to locate in a similar sized hole in the baseplate then hammered in to get a good fit once the coils had been wound.
I also made hardboard end stops to contain the wire as it was being wound on the core.
The core must be insulated. I used some thick plastic tape over wound by some PVC tape
The turned down part of the core was gripped in the lathe chuck and the gears selected to advance the wire by slightly more that the diameter of the wire (2mm)for each revolution. I used a slot cut in a piece of hardboard to feed the wire through.The lathe was set to a very slow speed. Every couple of layers I fixed with a layer of insulating tape.
I wound half of the wire on this core, the final diameter of my coils was about 2.5". With about 75 turns per layer with ten layers on each coil.
I then made up a base plate out of flat bar 1.25" X 0.5" X 6" with holes to fit the cores at 3" centers. If material had been to hand I would have used a thicker base plate. I subsequently added two additional plates to the base to try to reduce the magnetism losses.
I covered the completed coils with cloth and varnish to give it that old look. Also I made up a couple of pole pieces for the tops of the coils.
A switch was made from brass to cope with the considerable arc when the circuit is broken.
Each coil was wound in the same direction. The electrical connection was reversed to one coil to get the correct North South polarity. (Once I could work out which would be North or South, someone's right hand rule as I recall from long distant days of college. Now I don't bother, just connect it up and hold a compass near it and see what you get. ) Warning ! don't leave the compass near the coils at switch on or off as the pulse from the coils can reverse the compass so North reads South as I did on a number of occasions.
The coils were connected in parallel to get the most current from the available voltage. I use two car batteries in series to give 24 volts. The coils measure 1.2 ohms each this gives 20amps through each coil.
The magnetizer now works a treat. It is totally portable and can easily be taken to rallies where it has revitalized a number of magnetos so far.