Re: space winding?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Christoph Bohr" <cb@xxxxxxxxxxxxxxx>

Hello Robert

There are several reasons to space wind a coil.
I think you are referring to secondary coils, as the
primary coil is usually bare wire or tubing and thus
spacewound anyway.

Spacewinding will lead to a lower inductance of the
coil compared to a closewound coil, this is sometimes
usefull if you have a large secondary of wide diameter.
When you closewind such a coil with relatively thin wire,
the inductance will become unpractical big, or the winding
will be short. If you strech the same number of turns over
a longer distance, you can maintain  a more practical aspect
ratio, helping to reduce voltage stress between windings and
getting the end of the coil away from fhr primary to avoid constant
primary strikes.

Of course, you could still just use very thick wire to achieve a
similar effect, but this can become a cost and wight issue
with very big coils.

I feel like the first use if this technique might have been in the
early days, when the cotton/tar/whatever around wire could
not contribute a lot to its insulating properties.

I think for small coils this is not neccessary, except maybe to
gradually start spacing the wire in the upper section of the coil to
achieve a somewhat more graduate field where the wire finally
leaves the coil to join the toroid. But the shielding of the toroid
is probably the much bigger factor to avoid breakout on the last
secodary turns.
... just my two cents..

best regards

Christoph Bohr