Re: 12 inch spark, 1 inch flame.

Greetings All,

Still messing about with mosfets and I managed to get
a 12" spark (to a grounded rod). Unfortunately sparking
also broke out from the top of the coil. I saw an orange
glow from the coil, a little candle flame where the polythene
had ignited just above the coil.

No harm done  - the house burned down but I saved the
coil ;) Just a little hole in the top of my bucket - above
the windings. 

I had already put extra insulation on top of the coil -
I thinking of adding a thin layer of silicon rubber-
on the top few turns and above - both for extra
insulation and because its less flamable than polythene.

(Polythene has great electrical properties but it does
ignite melt, vapourise and ignite more easily than
say PVC. - coils tend to make a nice glow as they burn
to the ground.)

Ed suggested that the toriod was too close to the coil -
actually I think it was the opposite - the toriod needs
to be closer to the coil  - to give more electrostatic
shading - is there a rule of thumb for the toriods
hieght above the coil, and its diameter?

I'm only drawing about 2 or 3amp at 140v
to produce 12" sparks (300-400W). I'm
aiming for 2 or 3 kW by Christmas but
maybe not with a polythene former.

Even with this current though the output
transformer gets very hot. I'm planning to
put 3 E cores side by side, spliting a bobbin
in two using a bit of wood to keep the halves
aligned at the correct distance till I wind it.
But I've got myself confused, for the same
inductance etc do I only need 1/3 the turns
or 1/1.732 the number of turns (root 3)?

Have fun everyone.

Alan Sharp (UK)