RE: DC Tesla Coil - was rotary spark gap

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Lau, Gary" <gary.lau@xxxxxx>

Hi Dave:

Winding a primary out of 24 gauge wire sounds like a bit too thin?
Granted, you won't get excessive heating with only a 75 Watt power
supply, but primary losses will still be significant.

I also use a two-layer (copper tubing) primary, but with a fixed
geometry and conventional tapping for adjustment.  See
http://www.laushaus.com/tesla/primary.htm.  The two-layer construction
is a great way to achieve a high inductance without an excessively large
diameter primary.

Gary Lau
MA, USA

> -----Original Message-----
> From: Tesla list [mailto:tesla@xxxxxxxxxx]
> Sent: Monday, November 29, 2004 9:41 AM
> To: tesla@xxxxxxxxxx
> Subject: DC Tesla Coil - was rotary spark gap
>
> Original poster: "David Thomson" <dwt@xxxxxxxxxxxx>
>
> Hi Gary,
>
> Thanks for posting your work online.  Your designs are easy to follow.
>
> I haven't built a rotary gap yet.  But I'm moving in that direction.
My
> next coil will be a small 75 watt DC coil.  I'm going to experiment
with a
> variometer in the primary circuit for tuning.  The variometer will be
> modeled after one of Tesla's designs involving two flat spiral coils
on a
> sliding brass rod.  The centers of the coils will be connected through
the
> brass rod.  The coils will be wound with 24 gauge 1:4 ratio flattened
magnet
> wire.
>
> I wound two 13" flat spiral coils on 3/16" Plexiglas, one with the
windings
> going the same direction and one with the windings going opposite
> directions.  With just one 13" flat spiral coil, the inductance was
about
> 4.5 mH.  With two flat spirals wound in the same direction at 3/16"
apart
> and connected through the center, the total inductance was just 1.11
mH for
> the entire wire length.  With the same parameters but wound in
opposite
> directions, the total inductance was 121 mH.  The opposite wound coil
has
> other interesting properties as well.
>
> I'll use the opposite wound coils on a sliding brass rod to adjust the
> inductance in the primary circuit since it will give the greatest
range.
>
> I think that because I'll have so much control over the primary
resonance
> that I'll just use a static gap to begin with.  But since I have no
> experience with rotary spark gaps I can't help but wonder if I'm
missing out
> on an opportunity to significantly increase the frequency and overall
> performance.  What do you think?
>
> Dave
>
>  > -----Original Message-----
>  > From: Tesla list [mailto:tesla@xxxxxxxxxx]
>  > Sent: Sunday, November 28, 2004 5:10 PM
>  > To: tesla@xxxxxxxxxx
>  > Subject: RE: tungsten alloys for SG electrodes?
>  >
>  > Original poster: "Lau, Gary" <gary.lau@xxxxxx>
>  >
>  > Hi Dave:
>  >
>  > I've not attempted a spherical RSG contact, but I have attempted a
>  > cylindrical contact, perhaps with a similar underlying motivation.
My
>  > goal was to use as large a ROC as possible on the electrodes to
minimize
>  > the gap at which the RSG would fire, so as to minimize losses.
This
>  > attempt is illustrated on the lower half of my SRSG page at
>  > http://www.laushaus.com/tesla/sync_gap.htm.  I never did get that
gap to
>  > work reliably.  I have a half-baked theory that the larger
electrodes
>  > resulted in a longer effective dwell time, and the RSG wanted to
fire
>  > well in advance of actual alignment.  In the end, the propeller gap
with
>  > simple welding rod electrodes worked extremely well and better than
the
>  > larger cylindrical electrodes.
>  >
>  > Regards, Gary Lau
>  > MA, USA
>  >
>  >  > Original poster: "David Thomson" <dwt@xxxxxxxxxxxx>
>  >  > I realize you're building a rotary spark gap, but the tungsten
balls
>  > are
>  >  > excellent for a static spark gap.  I brazed the tungsten balls
on the
>  > ends
>  >  > of tungsten rods and they work great.  The balls on McMaster
Carr are
>  > grade
>  >  > C1/C2, which is very hard and doesn't pit.
>  >  >
>  >  > I'm now curious as to whether a spheroid contact would work with
a
>  > rotary
>  >  > spark gap.  I may try to build one.
>  >  >
>  >  > Dave
>  >  >
>