Re: Size DOES matter?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Steve,

At 05:10 PM 6/1/2005, you wrote:
> Hi all,
>
> I was pondering the relative lack of spark length from my DRSSTC. There 
> seemed to be no shortage of energy going into the thing. No parts were 
> heating excessively, so I assumed most of it was going into the discharge. 
> But the sparks were not so impressive. I was getting maybe 33" at any 
> breakrate above 100hz, and John Freau's formula predicts 40" for 5.5 joule 
> bangs at 100Hz.

From before, I worry that your buss voltage may be drooping from the scope 
photos...  If that is indeed the case, "fix that" ;-))


> What's more, they didn't grow that much with breakrate. I well remember 
> Richie Burnett writing about a classic coil that made maybe 14" sparks in 
> single shot mode but grew dramatically to 66" at 200Hz breakrate. (Richie 
> was not born yesterday so I assume he checked that the tank capacitor 
> charging voltage was the same in both cases.)

It seems after say 120Hz that the break rate does not change the spark 
length until you get to the point were the secondary is still ringing from 
the last break.  Then there are constructive and destructive effects that 
go on which can push the length further.


> Mine did 22" with a single bang and still only about 33" at 200Hz with 1kW 
> power input. (by way of comparison my classic coil did 40" with 1kW input 
> at 400Hz, and 17" with single bangs of very roughly the same energy.)
>
> So I got to thinking, maybe size does matter? Maybe the ultimate limit to 
> spark growth is not how much power/energy your oscillator can deliver, but 
> the size of the resonator? It's often been said that three times your 
> secondary length is the maximum spark length you should attempt. Well 
> maybe there is a law of physics that says you just can't get more than 
> that no matter how much power you supply!

My DRSSTC can run a vastly larger coil too (not done yet) :-))  But the 
primary cap voltages and stored energy go way up to so it is far from a 
direct comparison.


> So how could that be? Well for a start it's not too hard to see how toroid 
> size could influence spark length. Streamers need a certain field strength 
> to grow. And, the maximum field strength at the surface of any toroid is 
> limited to the breakdown strength of air. So it seems reasonable that a 
> smaller toroid might not "throw" the field (and hence possibly the 
> streamers) out to such a long distance: simply because it has less surface 
> area to accommodate field lines.

We are also playing with the fine line between disruptive and CW coils.  It 
appears that more than say 10 breaks just makes hotter streamers rather 
than longer ones.  So we need to pack all the "punch" into the first ten 
breaks to get streamer length...  I wonder what has happened if anyone has 
tried running a big pig type system into a "tiny" coil???  Did the tiny 
coil just incinerate itself, or did it's cap and system value changes 
needed just force it to a happy operating state?


> The resonator length may also have an effect. If we admit the argument 
> above, then the toroid should be brought almost to its breakdown voltage 
> for most efficient streamer throwing. If you try to drive a large toroid 
> with a small resonator then the resonator will flash over end-to-end 
> before the toroid reaches breakout. Hence (even with a breakout point) the 
> spark length will be limited by flashover rather than power availability.

Get a big toroid and find out ;-))  But it does seem one needs a big toroid 
just barely to the breakout point.  But DRSSTCs are goofy energy 
wise...  Thus my post weeks back about how we need to rethink all that 
DRSSTC energy stuff...


> To prevent flashover of an undersized resonator you need to reduce the 
> output voltage by fitting a breakout point and/or turning the peak power 
> down (this is achieved by loosening the coupling on a classic coil, or 
> turning down the DC link voltage- and increasing burst length to restore 
> bang energy- on a DRSSTC) The reduced output voltage will probably lead to 
> smaller sparks.

Making the secondary "too short" is a big problem.  I am running into that 
too.  But a smaller coil sure is far easier to "play with" in a small area.



> Does anyone have any comments as to whether any of this makes sense ;)

It seems to match what I am seeing too.  I am concerned if your buss 
voltage is drooping and causing unneeded problems if I am indeed right 
about that...

Cheers,

        Terry



> Steve Conner