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

Hi Steve,

I'd tend to agree that low voltage silicon switched tesla coils tend to be less efficient than HV spark gap switched systems, for the simple fact that a low voltage system requires far higher currents and lower copper losses than a typical HV SGTC design.

Most SS systems I've seen have Zchar values below an ohm, requiring milliohm-level copper losses to be efficient. The coppersmithing required here is usually beyond the home-depot off-the-shelf approach.

Still, with the relatively few coils that I've built, the SS coil outperforms the SGTC's by far, in terms of spark length/kW. The SS twin prototype shown here is operating at ~7kW and easily bridging 16ft:

The Zchar is only 0.75ohm, yet in can just bridge 18ft at 7kW, or about 2.5ft/kW. The larger 120L50k SGTC below will bridge about 25ft at 25kW, yielding ~1ft/kW:

The SS coil required a significant amount of coppersmithing to get the efficiency up. But I think the perfect quenching that a SS coil offers may the biggest reason it outperforms the SGTC coil. GL

Steve Ward wrote:

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

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


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

This could be of some help to You guys:


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


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