Re: [TCML] Solid state efficiency, was: mini Tesla coil specs

["Dex Dexter" <dexterlabs@xxxxxxxxxxx>]

Hi Steve,

The link I found/posted in the previous post is just an ordinary
tesla coil but with "IGBT gap switch" incorporated in the primary.
Obviously this type of coil differs from a DRSSTC in many details.
It has a very low characteristic primary impedance,very high peak
currents during operation etc.
I wonder if somebody measured first notch efficiency transfer for such
design (now I see the nickname is  OLTC)?
I agree it is probably lower than in well designed SGTC,and overall lower
than in DRSSTC (althought we are talking about forced excitation in DRSSTC).

It is also correct that SSTCs and VTTCs are less efficient given power input 
,but tell me one thing: do you know of SGTC which in a  single shoot burst
can develop 40"  long spark with peak secondary voltage only about 100 kV?
Well,VTTC can do that.
I guess you are taking my point.


Dex    

>
--- steve.ward@xxxxxxxxx wrote:

From: Steve Ward <steve.ward@xxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Subject: [TCML] Solid state efficiency, was: mini Tesla coil specs
Date: Wed, 11 Nov 2009 16:13:56 -0600

Dex, Id say yes, they (low voltage silicon switched tesla coils) are likely
to be less efficient (than HV spark gap switched systems).

In fact, the question of efficiency (in terms of spark length per input
watt) has yielded un-clear results in all of my ventures.  Basically, the
measurement accuracy of both power and spark length have enough error to
cover any claim that silicon based designs are more efficient than spark gap
designs.

My work has led me to believe a few things... A good SGTC and a good DRSSTC
will have about the same spark length efficiency per input power.  Ive heard
claims of SGTC performance that rival my best DRSSTC efforts (i think
Nemesis was one of these systems that seems particularly efficient).  In any
case, the DRSSTC doesn't seem to be exceptionally more efficient than a good
SGTC.  What i have noticed is that a shorter driving pulse to the resonator
(aka, energy transfer time) seems to be more efficient at producing the same
spark lengths with less power on my large DRSSTC system.  In order to do
this i had to lower the primary characteristic impedance so that the primary
current/voltage would ramp up faster.  In this test the improvement was
definitely clear, about 20% less input power for the same spark length
performance.  But what that 20% really means to a tesla coiler, i dont
know... The point i wanted to get to was that a SGTC system still dumps its
bang energy into the spark *faster* than i could manage with my DRSSTC.
Now, a SISG or OLTC (which function as the spark gap) should be able to
achieve exactly the same energy transfer time as a SGTC, but i have yet to
see results of one of these systems that shows it outperforming a well
designed SGTC.  So i think energy transfer time to the spark is very
important.  Take the extreme example of the quasi CW systems like the old
SSTCs and VTTC system that worked off of many mS long pulses.  These systems
can use huge "bang" energies, yet produce relatively short sparks. If the
same bang energy was delivered in just 10's of uS, the sparks would be many
times longer.

I wonder what ever happened to Mr Burwell... It sounds like he had a good
grasp on this (power semiconductor) stuff, someone i wouldnt mind chatting
with.

Steve
>
On Mon, Nov 9, 2009 at 5:33 AM, Dex Dexter <dexterlabs@xxxxxxxxxxx> wrote:

> This could be of some help to You guys:
>
>  http://scopeboy.com/tesla/t4spec.html
>
> I am just wondering if IGBT "gap" + primary of a very low impedance are
> more loosy than in normal spark gaps coils at typical Tesla coil
> frequencies.
>
>



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