Re: Another sad Aussie coil story!

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "D.C. Cox by way of Terry Fritz <twftesla-at-qwest-dot-net>" <DR.RESONANCE-at-next-wave-dot-net>


Don't feel bad Greg.  Many coilers overcouple their first units.  What was
the dia. of the secondary coil you were running?

I've developed a chart to set optimum coeff. of coupling based on the dia of
your sec. coil.  We use a primary to coilform horizontal distance of 1 1/2
inches on all our our coils both small and large.  This allows the chart to
work.

I've discovered than the distance of the sec. coil above the horizontal
plane of the primary coil is directly proportional to the dia. of the sec.
coil.

Some examples:

3 in. for a small 3-6 in. dia sec.

4.75 in. for a 8-12 in. dia. sec

7 in. for a 18 in. dia. sec

9 in. for a 24 in. dia. sec.

This assumes a copper tubing primary to achieve what I call a "uniform
inductance density".  This value of inductance density is higher with a
copper strap (ribbon) type of primary so the elevation usually increases 1/2
to 1 inch more.

The best test you can perform is to run your coil at 25-30% variac power
with the spark gap set rather tight, ie, .070 to .080 max gap.  They
experiment by elevating your sec. coil with some small 1/4 and 1/2 thick
plywood wedges looking for the very best spark output.  This assumes you
have already performed the normal pri tap tuning also at low power.

When you get the coeff. of coupling right, usually 0.18 to 0.20 range, then
your coil should run very smooth with no problems.

Another problem first time builders often face is what John Freau termed,
"racing sparks".  Racing sparks simply means you have to low a value of
capacitance on the primary and the coil is reaching highest potential at a
point somewhere below the top of the secondary winding.

Best regards and happy re-winding, something we all have to admit to,

Dr. Resonance




----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, June 27, 2002 7:10 AM
Subject: Another sad Aussie coil story!


> Original poster: "Mr Gregory Peters by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <s371034-at-student.uq.edu.au>
>
> Well, the new SRSG was working quite well, and the coil as making about
> 7-8 foot worth of sparks. Then the secondary decided to short a few
> turns and burn up. Murphy's law had to apply, meaning this happened ONLY
> on the side that I could not see from my position (otherwise, power
> would have been removed immediately). The coil was running in the dark
> outside and the only sign that anything was wrong was the sudden
> appearance of large clouds of smoke! I think the coil must have been
> overcoupled, as there are burns in several positions up the secondary (I
> should have listened to you Paul :)). The damage looks too bad to
> repair. Oh well, time to make a new secondary. Believe me, I wasn't this
> calm when it happened, that secondary cost lots of money! A word of
> advice to others: Never run a new coil by yourself without others
> present looking at the parts of the coil you can't see.!
>
>
> Cheers,
>
>
> Greg Peters
> Department of Earth Sciences,
> University of Queensland, Australia
> Phone: 0402 841 677
> http://www.geocities-dot-com/gregjpeters
>
>
>
>
>
>