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Re: [TCML] Spark gaps, Solid state switches and diodes

See in between your comments for my answers
Jim Mora wrote:

Hi Stephen,

What is your secondary former material?Is it coated inside and out with a
polyurethane or equivalent? Is the outside of the winding coated? Finally is
it a sealed tube say acrylic discs epoxied on each end?
The tube is PVC, the wire is sealed with polyurethane, but the ends are not sealed, and I guess the pvc could have absorbed some moisture 
As in all trouble shooting, making more than one change at time lends to a
doubling of problems. I would try to restore its original performance before
changing anything! 
If all things are equal and there is a big drop in output, I am wondering if
humidity has entered the secondary. I can think of lots of ways to
dehumidify it. I live in Southern Ca. and it gets very dry here! Maybe you
could open the ends and get it under heat lamps. Or a hair dryer? What are
the coil dimensions?

I willl try and dry out the coil and then seal it inside and out again.
.5'' Diameter, 20.25 winding length and 32 turns/inch so about 968 turns in total. wound on PVC former. The primary is 12.5 turns 13.5 inside diameter and 37 inches outside diameter. and in inch between turns. giving inductance range of 30 - 100uF for tuning. the Capacitor is 6.4nF per transformer as they are 15kV at 30mA each. so giving a range of 6.4nF to 38.4nF depending on how many I hookup. 
My 8" coil is powered 2*15KV/60 and gets 6 feet (1.83 meters) to a grounded
rod; this with a hyperbaric (air blown) single gap. Easy to clean, easy to
adjust! (2) 1" tapped threaded brass dowels suspended horizontally and
gapped end to end. After a couple of runs I simple unscrew one of the dowels
and burnish the ends with 400 or 600 grit which really makes difference!
Polishing helps a bit too. This is a Richard Quick design and is in the
archives.

I'm definately going to try one of those Hyperbaric Chambers first...
Thanks for the advice...!

Stephen Hiscock


Welcome Back!
Jim Mora

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of DC Cox
Sent: Thursday, January 29, 2009 8:56 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Spark gaps, Solid state switches and diodes

If you want a quck and inexpensive fix try my hyperbaric sparkgap.  At this
power level perhaps two in series, but  try one first.  The vac. cleaner
motors are nearly or sometimes free at large
vac cleaner repair shops.  Plbg fittings from local large hardware store
(usually brass fittings), and some 3/4" copper pipe (Home Depot).

You should disconnect your power xmfrs and test all individually to be sure
one hasn't died.

The SISG gaps also provide high performance, but at a price.

Dr. Resonance




On Thu, Jan 29, 2009 at 8:46 PM, Stephen Hiscock
<stephenhiscock@xxxxxxxxx>wrote:


Hey guys, my name is Stephen,  I've just joined this email group.

I work as an electrical Engineer and I've been playing with Tesla Coils

and

High voltage for about 15 years or so, and built a fairly powerful Tesla
coil about 10 years that made over 1 metre (3-4 feet ) sparks.

It was just Neon Sign powered (I had 6 in parallel) and had a conventional
spark gap, but it never performed as well as I would like. I fired it up

the

other night after dusting it off (it had been in my garage for a bout 5
years), and it performed dismally only getting about 1-2 foot sparks.  I
played with the spark gaps etc and got it performing a bit better, but
nothing like it used to go.

I'm thinking that I'm wasting a lot of energy in my spark gap. in fact tow
nails hammer into wood seemed to perform the best (quenching issues?)  So

I

went online and after a while came across Terry Fritz's plan for a solid
state spark gap, but his plan only seemed to be for a relatively low

powered

MOT tesla coil. (a few hundred watts)

I'm wondering if anyone who has had first hand experience with these solid
state spark gaps (SISG) could help me answer a few questions
* My transformers put out 15,000 Volts at 30mA each x 5 (or 6 if the fuse
doesn't blow ;-) ) so how many will SISG's will I need
* how reliable will his general design be with my coil. (obviously I will
need more in series - but will I need to parallel them as well??
* Is there an easy way / simply formula to calculate how much current will
be flowing peak? (800A or 8000A) - depends on resistance or capacitance or
inductance? - I currently don't have an oscilloscope at home I can use.
* How much power gets wasted in the reverse diodes - normally the voltage
drop across a diode is 0.7 volts - so does that mean if I'm getting 1000A
peak average in the primary I will be wasting about 700 watts as heat

across

the devices and possibly more depending on how many devices I have? or am

I

missing something? - this would seem worse than the conventional gap - but
everyone seems to rave about the performance of SISG and DRSSTC coils.
perhaps its about peak energy levels (not average) and then 700 peak watts
compared to 15MW peak energy  is not much?
I think I just answered my own question. ;-)

Sorry for so many questions, but you guys seem to like answering questions
- and I've been enjoying the discussion - so hopefully I've added

something

more to chat about.

so to be simple - how easy will it be to scale his design (SISG) to my

coil

or will most components need to be upgraded.

Stephen



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