RE: [TCML] 20KV primary drive voltage tips ?

["Lau, Gary" <Gary.Lau@xxxxxx>]

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of Chris Swinson
> Sent: Friday, February 29, 2008 10:03 AM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] 20KV primary drive voltage tips ?
>
> Hi Gary,
>
> >15/30 NST's are commonly used with a sync RSG.  So a simple 15kV NST is out
> >of the question?
>
> Well other than cost and actually locating one, would be far easier just to
> use a NST which could peak to 20KV, I only have 10KV so choke charging would
> be the only option.

I guess like "W" says, ya fights with what you got!


> >> I know my 10KV primary is spaced out about 0.5" so I assume a 1" gap
> >> between
> >> turns will be needed ?
> >No, you should be just fine with 0.25" between turns.  A 1" gap will make
> >the primary needlessly large.
>
> I'm not so sure,  0.5" was about the min distance I could cope with with
> 10kv.. I am hoping not to need a great number of turns also

Yeah, if you have only a very small number of turns, they the spacing needs to be comparably wider.  But remember that gap losses increase significantly as primary inductance goes down.  Most report much better performance as Lpri increases.


> >> The 20KV drive should help spark gap quench times ?
> >I don't know that I've heard that bang voltage correlates with quench time.
> >> Ideally I want to aim for 1st notch quench and keep the transfer cycle
> >> time
> >> to 3 cycles maximum( so >0.3K needed)
>
> >Quenching suffers as K is increased.  It's not even clear that first notch
> >quench is the best thing for streamer production.  And running with a K of
> >0.3 is simply unrealistic.  >You'll get racing sparks long before achieving
> >anything close to that.
>
> It the same issue I think as increasing the tank size, too much current/heat
> effecting quench times. A higher voltage over current shouldn't heat the gap
> and as there is physically a larger gap, should quench better... AFAIK..

True enough.


> >> 20KV will probably suffer from corona on the primary, but that will have
> >> to
> >> be delt with if/when it happens.
> >I've never noticed any.
>
> Well thats a good sign then. Was some conflicting views on this a while ago.
>
>
>
>
>
> >> I also want to keep the coupling as tight as possible. Going by my
> >> simulations 0.38K seems to be the maximum before hitting problems. Also
> >> should a cone or vertical primary be used ?
>
>
> >What simulator predicts coupling problems?  Predicting racing sparks is one
> >of the unsolved mysteries of coiling.  I'm unaware of any method of
> >predicting it beyond noting >the experience of many coilers, where coupling
> >much above 0.15-0.20 seems to be unmanageable.
>
> http://www.future-technologies.co.uk/IMPULSE/simulation.htm
>
> coupling tests are there, though I did a 0.45K simulation as it showed up
> the problem a lot more than a low value. 0.38K appeared to be the maximum
> before the strange humps in the waveforms.

I couldn't comment on the strange humps, but the simulation makes no attempt to predict racing sparks, which WILL destroy your secondary long before you get close to 0.3


> >A vertical (helical or solenoid) primary is typically shunned in favor of a
> >flat spiral primary, for the very reason of having TOO high a coupling.
>
> Understood, but if I do go for higher coupling then it could work out better
> for me in that respect.

Again, let racing sparks be your guide to coupling rather than a waveform simulator.


> >> Onto the key points now, the last system I built was 500khz 10KV, so 20KV
> >> should allow a 1mhz coil to be used.  Really its half the inductance and
> >> double the voltage input to get the same spark output. A bit of a long
> >> story
> >> for another day that one!
>
> >I don't follow your logic.  The experience of most successful coilers is
> >that larger coils make for bigger sparks, and that larger coils inherently
> >operate at lower frequencies.
>
> True to a point, though there was a huge talk about this on the list not to
> long ago. That area of coiling has been "done to death" already. I am
> seaking a new direction based on my own ideas. Fail or not, im going to do
> it anyway ;-)

No problem with that!

> > I am aiming for 1ohm DCR on the secondary. the larger dia wire should help
> > with the running at 1mhz.
>
> >The DC resistance of the secondary is of little importance, given that the
> >load (streamer) impedance is many orders of magnitude higher.  AC
> >resistance will be far higher, >especially if you're talking about 1MHz,
> >but I still don't think it's a major consideration.
>
> True, but I am going to do it anyway.
>
>
>
> >> The secondary form will be 6.3" dia and about 50-60" tall. A lot of
> >> figures
> >> to crunch up and some compromises no doubt.
>
> >Yours would be considerably more candle stick-like than most well
> >performing coils.
>
> True, my coil could be made better though I am more into alternative "fun"
> with coils than producing long sparks.
>
>
> >> The design is to start at 500watts input power as before, keeping the
> >> secondary size physically the same size, but just using a larger dia
> >> wire.
> >> Will run at a higher frequency and have less turns/inductance hence the
> >> need
> >> for a 20KV input.
>
> >I'm not sure that the secondary geometry cares what the primary bang
> >voltage is.  One typically sizes the secondary by the bang-SIZE.
>
> The idea was based on some tests I did years ago, during SSTC work among
> others. I built so many coils and tested so many aspects of the coil. Really
> twice the voltage and half the inductance is not hard to accept or
> understand. Not saying thats solid exact fact but trying to keep things as
> simple as possible to give a overview of my intended design.
>
> >I hope this helps!
>
> All input is of course welcome :-)
>
> I think probably that most will think its a waste of time and won't work,
> but I've done the "dead end" road already and want to have some fun with
> what I think will work out as higher Q systems. I think the data collected
> from the experiments will be nonetheless very interesting.  Its a lot more
> interesting to experiment with ideas then just going to build a large
> dia/inductance coil like everyone has been doing for the past 50 years or so
> ;-)
>
> Chris


OK, critical thought is always welcome here.  Just trying to attach some explanations to predictions.

Regards, Gary Lau
MA, USA
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