Back to magneto magnetising

[andy pugh]

I am playing about with the magneto magnets again.

I have several flywheels, though only one with a usable cam surface in the hub.
So I am playing about with the others.

Magnetising the semicircular magnets out of the retaining ring seems
to work quite well, as you get a good contact with the pole pieces on
the charger. But then when you put them back together again N to N and
S to S it seems to leak away.

I have managed to increase the magnetic field from about 30G to 80G.
But don't know if that is enough.

(I am measuring the field with a home-made gaussmeter:
https://hackaday.io/project/185106-magnetometer-gaussmeter-teslameter
In fact I got a bit distracted by that project away from the flywheel.
But it does let me get a better idea of what is working and what is
not.

I am pondering the idea of making new pole-pieces to replace the
existing laminated ones, and then glueing a layer of modern magnets to
the surface thereof. I think that would definitely beef up the spark
(and improve the lights) but would be an unfortunate departure from
originality.
I might still do it out of interest, though.

Then there is the plan of making a more beefy magnetiser. Currently I
have about 25,000 AT and a core with 0.75 sqin area. The Lucas guide
suggests 75,000 AT and a core of 9 sqin. But that ends up huge, and
needs a collossal amount of wire.

The calculations for a charger are interesting. Once you have settled
on a voltage and core size then you can set the AT by choosing the
wire diameter. Oddly adding more turns does not then give more AT as
the increase in turns is exactly matched by the increase in
resistance.

But, more turns does reduce the current and power significantly.

A 50mm round core with 1000 turns of 1mm wire and 240V power is 70,000
AT, 70 Amps and 17kW of power. And needs 1kg of copper wire. Whereas
9000 turns is 10kg of wire (£160) but the current drops to 6 A and the
power to a more reasonable 1.8kW.

But now I am wondering if the flywheel might have been charged in-situ
with the coil armature as a keeper. This is very much the norm with
later magnetos. But it would need a lot of field to magnetise through
the brass flywheel rim.

--
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1912