[Prev][Next][Index][Thread]

Re: Primary/secondary spacing



Tesla List wrote:
> 
> Subscriber: sfalco-at-worldnet.att-dot-net Thu Jan 23 22:09:31 1997
> Date: Wed, 22 Jan 1997 19:24:24 -0500
> From: Steve Falco <sfalco-at-worldnet.att-dot-net>
> To: tesla-at-pupman-dot-com
> Subject: Primary/secondary spacing
> 
> Does anyone have a rule of thumb for the spacing between the inner-most
> turn of the primary and the secondary?  I'd like to make my new coil
> fairly compact, but without it arcing over.  I have heard that the
> primary turn-to-turn spacing should be about the same as the diameter of
> the primary tubing (say 1/4" to 1/2"), but I have not seen anything on
> the primary/seconary spacing.
> 
>         Steve Falco
>         sfalco-at-worldnet.att-dot-net

Steve, 

It depends on whether you insulate the innermost turn, and whether the
innermost turn is at ground potential. If you run with  a neon
transformer source, the innermost turn will be running at 1/2 the HV
supply voltage. With this situation, and a bare primary, allow at least
1" all around. This spacing can be reduced somewhat by slipping a piece
of clear vinyl or Polyethylene tubing around the inner-most turn, but
you run the risk of getting excessive corona. Most of your primary
inductance comes from the outermost turns anyway, so don't try to make
things too tight here - give your secondary a little more space.

Even with a grounded inner turn, if your secondary winding is positioned
such that it begins at a point below the plane of the primary (i.e.,
higher "k"), you can still get flashovers from higher potential points
on the secondary to the primary. For this reason, larger coils may need
to run with larger primary-secondary spacing - 1.5" to 2" all around
should be more than adequate. 

Safe coilin' to you!

-- Bert --