RE: [TCML] Spark gap

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

Comments interspersed:

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of bartb
> Sent: Saturday, February 23, 2008 11:59 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Spark gap
>
> Hi Gary,
>
> Lau, Gary wrote:
>>  1) If your power supply is indeed rated at 200mA, that's pretty beefy.  Most static
>> gaps are used at much lower power levels, and may have trouble with the current
>> you're talking about.  A rotary gap may be better here for that reason alone.
>
> My NST is absolutely rated beyond 200mA. Definitely beefy! I don't see
> how smaller current supplies suffer? As a matter of fact, the gap I use
> now was first used with the NST before it was modified into a beast. The
> notable difference in the gap was not due to it's "beef", but long
> before when it was a simple 12/60. I don't at all understand your
> statements on this point? Forgive me, but I just don't.

I'm not sure I'm following you, and I don't see where I suggested that smaller current supplies suffer.  I was trying to point out that static gaps don't perform well with very high powered (beefy) power supplies.  Pole transformers, potential transformers, even MOT's, do much better using RSG's over static gaps.  I'm not certain just where to draw the line, but I would put a 200mA PSU on the beefy side of the line.


>> 2) Any static gap, RQ or otherwise, is unlikely to operate at 60BPS, or 120BPS.
>> All static gaps operate in what can only be described as a chaotic mode, with the
>> BPS varying widely from second to second.  A long-term average is typically far
>> higher than the mains frequency, usually in the range of 150-300BPS.

> I disagree (someone, shoot me now). The static gaps (RQ or otherwise)
> will operate at their caps ability to charge to the breakdown voltage
> and no less. This is simple. I agree that there are a lot of gaps that
> will operate at much higher bps than 120 on average, but it doesn't
> "have to be this way". The fact is, "it has been this way needlessly".
> It is simply the rate of charge vs the arc voltage. There is nothing
> else to affect this except that maybe the arc voltage is varying
> (usually the cap and transformer are static and the gap status is the
> variable). I've seen many "others" designs run rather fast bps and
> rather low cap voltages. I always wondered "why would they do that"? It
> didn't take long to realize "they didn't know any better". They simply
> didn't evaluate the numbers and what they got (is what they got). BPS is
> easily controlled in a static gap just as easy as an SRSG. But, if no
> one "knows how", then it won't be controlled. I think this has been the
> real cause of what you've stated.
>
> A cap can only be charged at some rate by the voltage and current
> feeding the cap only so fast. A gap can only arc at a given potential
> based on geometry and distance. These two situations make for a rather
> consistent firing voltage. But, if you don't realize this "before you
> build", anything can happen, and usually higher bps is the result (at
> least in the coils I've evaluated). But I have no control over another
> coilers coil. All I can do is advise and try to make my case. I've done
> it, and I don't see why others can't except maybe it's not that
> important to them? In any respect, I'll stick to the physics and my own
> experience. I also note others experience. An evaluation usually tells
> the tale why.

Measuring the actual BPS rate on a static gap has always been difficult.  The only way I know to measure it is by using a storage scope and counting the bangs in some time interval and doing the math.  Have you actually scoped and measured your BPS?  I have, and this is how I arrived at the numbers I cited.  Particularly when using LTR caps with a static gap, non-linear ferro-resonance effects cause totally unpredictable secondary currents far in excess of the faceplate rating to occur, and I don't believe that any method exists to reliably calculate BPS.


>> For NST's (the only thing I have personal experience with), a sync 120BPS RSG
>> is better than a static gap because it allows one to use a larger cap, resulting in a
>> larger bang.

> Do me the service in explaining "how" an RSG is better than a static gap
> in your described situation.
> In other words, "why" does an RSG allow a larger cap size?

Let's first recall that in the tables which recommend the optimal capacitor size based on the transformer, there are separate columns for static gap and for sync RSG, the sync RSG using a much larger cap.  With my 15/60 NST and a static gap, I found that a .02uF cap worked best.  Anything larger caused excessive current draw and ran poorly.  But the same NST with a 120BPS sync RSG ran best with a .04uF cap.  I wish that I could explain why that a SRSG allows a larger cap to be used without a lot of hand waving, but it is a well documented fact.  Do you disagree?

I suspect it goes something like this - In the static gap, say the cap is charging upwards, but doesn't quite make it to Vgap before the mains polarity flips, and now it starts "charging" downwards.  The energy in the cap to that point is not lost - rather it transfers to current in the NST secondary.  This saturates the NST shunts, causing even more power to be drawn and accelerating the charging of the cap in the downward direction.

>> Spark length is all about using the biggest bang possible.  And it guarantees that
>> each bang is identically and maximally sized.

> Is it? Why? Sorry about that Gary, not trying to be a butt-head, however
> when statements without why is made, I have to ask why or what backs up
> those statements. I know where you are coming from. I'm questioning much
> these days so I may seem an arrogant ass, but I'm really just trying to
> get some info to back up statements.

I assume you're questioning the part about spark length being correlated with bang size?  I think it was one of the folks (maybe Finn?) with a DRSSTC who had the ability to vary bang parameters independently, found that varying just the bang BPS varied the streamer brightness but the length was relatively unaffected.  But varying the bang size directly affected the streamer length.  So, optimizing a TC to have the largest bang size at a relatively slow BPS will yield the longest, thinnest sparks, while choosing a small bang size at a very high BPS will yield shorter, but brighter sparks.


> Best regards,
> Bart

> > Regards, Gary lau
> > MA, USA

_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla