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

[Steve Ward <steve.ward@xxxxxxxxx>]

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.
>
>
>
> Dex
>
>
>
>
>
>
> --- pbbrodie@xxxxxxxxxxxxx wrote:
>
> From: "Paul Brodie" <pbbrodie@xxxxxxxxxxxxx>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Subject: Re: [TCML] mini Tesla coil specs
> Date: Sun, 8 Nov 2009 16:59:14 -0500
>
> Unfortunately, the http://home.hiwaay.net/~eburwell<http://home.hiwaay.net/%7Eeburwell>link is no longer
> active. :-(
> Paul
> Think Positive
>
> ----- Original Message -----
> From: "S&JY" <youngs@xxxxxxxxx>
> To: "'Tesla Coil Mailing List'" <tesla@xxxxxxxxxx>
> Sent: Sunday, November 08, 2009 1:03 PM
> Subject: RE: [TCML] mini Tesla coil specs
>
>
> > Herr Zap,
> >
> > Here is a description of one SCR driven TC, circa 2000:
> >
> > Original Poster: "Eddie Burwell" <eburwell@xxxxxxxxxx>
> >
> > Well, from my experiments with SCR based coils IGBTs look like the hot
> > ticket. IGBTs like SCRs are four layer devices and have "fixed" voltage
> > drops. This means the power lost in the switching device goes up linearly
> > with increasing current rather than I^2R as does a mosfet. The IGBTs have
> > some nice advantages over SCRs namely they turn on fast and they can be
> > switched off.
> >   I tried using saturable reactors to effectively speed up the turn on
> > time
> > of the SCRs which works but causes other problems ( like holding the SCR
> > on
> > for an excessive period of time.) So I ditched the saturable reactors and
> > went to a 365A 1800V 60uS Tq SCR. This sucker is rated for 8000A peak.
> > This
> > works OK except that the SCR doesn't turn off until the primary cap is
> > almost empty. No first notch quenching:-(. In order to get first notch
> > with
> > a 100KHz coil a Tq of 5uS would be necessary. Unfortunately 5uS SCR are
> > kind
> > of rare and don't usually exceed 600v.  As you head towards lower
> voltages
> > and higher currents and more capacitance keeping the inductance low
> enough
> > to hit the target resonance frequency becomes difficult. Not to mention
> > how
> > absurdly careful you need to be in order to minimize parasitic
> inductance.
> > If your cap has as much inductance as your primary then your primary will
> > only see half the voltage. This sort of thing can happen when your
> primary
> > has only one turn.  So higher voltage is better!
> >  A 1200V IGBT is sufficiently fast and can be turned off, but there
> > remains
> > one question. How far can they be pushed past their current rating for a
> > pulse? A 100A SCR can do 1000A for a brief pulse. Could a 45A IGBT make
> it
> > to 450A? The ratings on IRG4PH50U say 45A cont. 180A peak but there is no
> > indication in the data sheet as to how the max peak current relates to
> the
> > with of a pulse (for infrequent pulses). If They can hit 450A look out!
> >  With my last experiments in solid state coiling I could pull about 18"
> > with a 1 joule cap fired 400 times per second. The SCR was barely warm.
> > quality caps are an absolute necessity! I started with some CDE SCRN222s.
> > Their internal connections were so poor the terminals got hot although
> the
> > rest of the cap was cool. With 10 joules per bang an IGBT coil should
> > start
> > to really perform!
> >
> > To see my outdated web page with some of my early work look at:
> >
> > http://home.hiwaay.net/~eburwell <http://home.hiwaay.net/%7Eeburwell>
> >
> >
> > Oh yeah.. IGBTs typically have internal anti-parallel diodes rated for
> the
> > same current as the IGBT. Convenient..
> >
> > -----Original Message-----
> > From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf
> > Of Quarkster
> > Sent: Friday, November 06, 2009 10:50 AM
> > To: Tesla Coil Mailing List
> > Subject: Re: [TCML] mini Tesla coil specs
> >
> > Hi Paul -
> >
> > Since you had also mentioned driving a coil with a SISG switch, I wasn't
> > sure if "SRC" might be a new type of power switching circuit that you
> > might
> > have discovered somewhere. I suspected that you might have meant SCR, but
> > I
> > thought it would be better to ask for clarification.
> >
> > In some industrial power-control systems, strings of series-connected
> SCRs
> > are used to obtain the high standoff voltage ratings required. Large
> > arrays
> > of series-connected high-voltage, high-current SCRs have shown up on eBay
> > that have power ratings of hundreds of KW. However, I think these are
> > primarily used in pulse-width-modulation power control of resistive
> loads.
> > SCRs typically have rather slow turn-on and turn-off characteristics,
> > compared to IGBTs or MOSFETs, so they are not optimum for any application
> > that requires high-frequency switching.
> >
> > Over the years, there has been a fair amount of discussion on the TCML
> > concerning the use of SCRs as switches in Tesla coil primary circuits
> > (search the TCML archives at www.pupman.com). However, I don't recall
> > anyone
> >
> > ever actually building a SCR-commutated Tesla coil. (If anyone is aware
> of
> > a
> >
> > Tesla coil that successfully used SCRs as a primary switch, please speak
> > up!)
> >
> > SCRs are used very successfully to drive high-voltage generators based on
> > iron-core automotive ignition coils, but this is quite different than a
> > resonant Tesla coil.
> >
> > Regards,
> > Herr Zapp
> >
>
>
>
>
>
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