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

["Dex Dexter" <dexterlabs@xxxxxxxxxxx>]

These are great (and BIG) coils Greg!
With 100 BPS @ 25 kW operation  120L50k would create even 
longer discharges than at 350 BPS @ 25 kW I guess.
Do you (dis)agree?
BTW, compared only loss of IGBT in OLTC and spark gap
loss in SGTC (at same power level and BPS) which one is higher
at tesla coil frequencies?


Dex

   
>
--- lod@xxxxxxxxxxx wrote:

From: Greg Leyh <lod@xxxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: [TCML] Re: Solid state efficiency, was: mini Tesla coil specs
Date: Sat, 14 Nov 2009 11:40:18 -0800

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:
http://www.lightninglab.org/misc/NLL_Prototype.jpg

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:
http://www.lightninglab.org/gallery/2008Teslathon/images/120L02.jpg

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
> 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
> 


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