MAGNETS and Magnet Chargers
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Figure 1: Typical magnetization curves for common magnetic materials.
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Graystone Ltd., 3437 Blue Ball Road, North East, Maryland
21901
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How many times have your restoration projects required a magnet
charger? Maybe you have a magneto which seems to be all in order
but might need a bit more magnet strength to produce a reliable
spark. I have successfully recharged the magnetos on both a '23
Fordson and a '26 Model 'T' using my home-built
chargers. The '23 Fordson has started on three to four turns of
the crank over the last three years. I have riot tried to start the
'T' yet but expect similar results. I like being able to
run these off the flywheel magnetos instead of an external battery;
very rewarding. Sometimes recharging a weak or dead magneto magnet
will bring an otherwise fine engine to life, saving the owner
considerable expense.
In recharging the Fordson and the 'T' magnetos, which I
think are the most challenging, I have built two magnet chargers
and feel that I am one of many self-proclaimed, de facto experts on
the subject. Until recently, I just built the chargers, they worked
and that was the end of the story. A few weeks ago I thought I
would try to explain to GEM readers what is important in building a
charger and how to go about achieving it by several means. Not
everyone has the same junk box as I, so some other options would
surely help the budding builder of magnet chargers. Charging
magnets is not difficult if you understand the rudimentary
principles by which they function. It is like driving to Buffalo;
several routes are possible, all get you there and some are more
difficult than others. The following is written for both the
'weekend warrior' who merely wants results and cares not
about the gory details/theory, and for those of a scientific ilk
who want to know how everything works.
The first thing which is important in building a magnet charger
is to set up a magnetic field by wrapping wire around a cylindrical
core and passing a direct current through it. The wraps need to be
neat; starting from one end of the core to the other with several
layers is usually required, all turns being in the same direction.
How many turns you wrap depends on how you plan to energize the
magnet. My first attempt took the high current road via a DC welder
as the current source. (The welder has to be DC output or you can
kiss any magnetism remaining in your magneto goodbye!) The welder
had an output of about 140 amps possible so I used about number 10
insulated wire. This is large wire. On my core, which was about 7/8
inch diameter by three inches long, I was able to fit about 30 to
40 turns on each pole. What determines the strength of the magnetic
field set up is in part the current times the number of turns of
wire or simply the number of amp-turns. My first setup produced
about 4000 to 5000 amp turnsnot too bad. This setup was cumbersome
to use, as I had to use it in the garage where the welder was, the
coils got hot really quickly and I had to avoid the arc from
touching the stinger to a plate used to turn the current on and
off. There was a lot of waiting time needed to allow the coils to
cool. For a Fordson magneto where there are 16 magnets, you need a
lot of on time for the charger so this may pose a problem. If you
are zapping a hit-or-miss magneto to freshen it up, this may be
okay if the welder is all you have.
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