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Re: Bang size and break-rate
In a message dated 99-06-10 04:47:31 EDT, you write:
<< I should mention that it doesn't matter how the large bang is
>> created, i.e. either by using a large cap, or a higher input voltage,
> > the main thing is the large bang size and low break rate. The higher
> > voltage might even be a little more efficient due to lower gap and
> > other tank losses. The corona onset point is of course the limiting
> > factor for using higher input voltages.
> snip.
>
> > John Freau
> I get a strong sence of "katharsis" reading this, since I am running
> MMC`s from a 20 kV RMS pig, and have not forgotten the initial responce
> that I got to this homemade pig, where it was pointed out to me, that I
> should have gone for lower voltages, and saved the high voltage for the
> magnifier.
Finn,
You raise a lot of important issues here. I agree that old TC beliefs
must be constantly questioned. I never could see why a magnifier
should use a higher voltage than a regular TC. I don't think a maggy
works much differently than a normal TC.
> But what I have in mind specially now, is a discussion about how we
> build coils today.
> 800-not much more than 1000 turns secondarys.
This is an issue that I'm interested in also. My secondary uses 1500
turns, and seems to be efficient. I may do some tests with a smaller
number of turns to compare. The only advantages I see of using more
turns are; lower frequency, and maybe lower gap losses.
> preferably more than 10 turns primarys.
There has been endless discussion and disagreement on this point.
It is interesting that Skip Greiner built a sync gap TC that used the
same cap size and NST, as mine, and got the same spark length,
although he used 230 turns in his secondary and I used 1500. He
used 5 turns in his primary, I used 24.
> topload 2-3 times bigger than sec. self-C
This would seem about right, are you suggesting something different?
> a cap that matches sec. system res. freq.
> power: untill it burns up. :-)
> I have seen, how my sparklength increases, if I apply the available
> power through a wide sparkgap, thus high voltage, and low breakrate, as
> opposed to a narrower gap, with lower voltages and a higher breakrate.
> This is a highly resonant charging system, with a static gap, where only
> my nerves, and ultimately the cap, sets the voltage limit.
> If we assume that the secondary system is optimized, with a high Ctop,
> and we want to increase the bang size, keeping the voltage, and
> breakrate fixed, the cap must be increased in size for more bang. This
> in turn requires the primary to be tapped in at fewer turns.
If we make the coil physically larger too, it will have higher inductance
in both primary and secondary. Although the coil may use few primary
turns, the inductance will be higher. It is the inductance which is the
real key, more so than the absolute number of turns, since gap losses,
and tank surge impedance are controlled by the relative proportions of
L and C in the tank, rather than by the absolute number of turns. For
the same L, a large diameter coil will have fewer turns.
> It is my impression, from my own experience, and from looking at
> numerous sites, that the first coil that a person builds is made to meet
> the "many primary turns" criteria, the next, and bigger coil is
> frequently not. Many of the big coils have 4-5 turns primarys, Bill
> Wysoc`s model 14 has only 2. (ok!, it`s a maggie, but still...)
The many-turns-primary is not universally advocated, even for
small coils. There are many experts who just as strongly advocate
a very small number of turns. I myself have not explored the issue
enough.
> So, is there some mechanism inherent in really big coils that allow for
> these low primary turns counts, or are the newcomers making a lot of
> primary turns in vain, for the sake of a (perhaps) outdated tradition.
My guess is there's nothing different about the large coils that would
demand fewer turns, especially if the coils are physically proportioned
the same.
> If not, I would feel tempted to push for 30 kV in my next design, for
> low C, high L, even though I alresdy have experienced some of the
> problems of insulating to 20 kV in my present tank circuit.
In some tests I did of small cap vs. large cap, I didn't really see any
difference. The voltage was varied to keep bang size the same, and
the spark length was the same. I used a .0077uF cap, vs. .0147uF
cap, and adjusted the voltage input, to keep bang size the same;
the spark output was the same length. So this test could also be
considered to be a voltage comparison test depending on how you
look at it. If the gap losses were greater at the low voltage, it didn't
show up in the spark length. So any theoretical differences must
be slight in the real world. (Reinhard will be glad to read this ! :)
I agree there is still much work to be done to completely explore
the issues you raised.
Cheers,
John Freau
> Cheers, Finn
>>