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Sigurthr

Tue Mar 22 2016, 07:27PM

Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597

I found the old reference I used: See:

Hazmatt_(The Underdog)

Wed Mar 23 2016, 03:25AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

I did quite a bit of work on this, but nobody ever really seems to give a damn, but I'll go ahead and post it one more time,

Sigurthr

Wed Mar 23 2016, 05:29AM

Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597

Interesting, Hazmatt! I was unaware of that thread and your work therein. It looks like my Phi multiplier is close to your exacted value.

Perezx

Wed Mar 23 2016, 07:29AM

Registered Member #54263 Joined: Thu Jan 15 2015, 09:54AM
Location: Perth
Posts: 35

What type of capacitors do you have? They are soooo different...
And tell us details on your primary/secondary configuration, please

Uspring

Wed Mar 23 2016, 11:54AM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
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Posts: 711

Hazmatt, I can't quite follow the math in the older thread you referenced. What would be your suggestion for the 10KV 50ma NST of the OP?

Gordie Orange

Wed Mar 23 2016, 02:11PM

Registered Member #55076 Joined: Sat May 23 2015, 08:26AM
Location:
Posts: 20

These are the caps I used
http://www.ebay.co.uk/itm/251504542592?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

I'm in the UK so the NST is 10kv, 50ma at 50hz (am i right in thinking a 6kv 100ma will give me bigger sparks?)

I have a 6" secondary thats about 30" high and a 6x24" toroid and a static gap of 6 copper tubes (i'm looking into a rotary gap but my brain is melting)

Hazmatt_(The Underdog)

Wed Mar 30 2016, 03:25AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Hi Uspring,

1. Find your Z first
2. Calculate for C using Z, this is going to give you a resonant value for C
3. Then just multiply C by 1.4, this gives you your LTR C value.
It turns out to be 1.4 because this relates to the peak current in the charging cycle. (should really be 1.414, but 1.4 or 1.5 is really close)

The actual importance of the calculations was an accurate and faithful derivation of C LTR, which was verified in simulation of course because it converges everything to impedance's, so naturally they should match up.

Uspring

Sun Apr 03 2016, 02:01PM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
Location:
Posts: 711

Thanks, Hazmatt. I'm not sure about how to obtain Z. Assuming e.g. a 50ma rated NST, does that imply a 50ma short circuit current? If that is the case, one can obtain the approximate leakage inductance by V/I = 2*pi*f*L. This is approximate since, there is also a resistive component limiting the short circuit current.
I've found by some equation jiggling, that in the case of 2 burst per primary current cycle, the burst should best be around the zero crossing of primary voltage. That gives max voltage for the tank cap. For the choice of an optimal tank cap, voltage is maximized in the resonant case, but energy is somewhat larger for a higher capacitance value. This agrees with a preferred larger than resonant value.
The best value is the result of an transcendental equation, so it is not sqrt(2)*resonant value, but not too far away from it.

Hazmatt_(The Underdog)

Sun Apr 03 2016, 03:30PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Uspring, just follow the link in my previous post, it calculates everything.

Uspring

Sun Apr 03 2016, 05:40PM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
Location:
Posts: 711

It looks like your prescription is:

Z = Zbranch + Ztankcap

First, why should be this so? Z, i.e. Vtransformer/Itransformer is not a source impedance. A good transformer should have a near zero impedance.
Secondly, Zbranch and Ztankcap don't simply add up this way. Note that Zbranch contains inductive components and Ztankcap is a capacitor. You calculated Zbranch correctly (sqrt of sum of squares), but didn't add Ztankcap in the right way.
Thirdly, you used only 61H and 17k from one side of the transformers leg. Actually you have 2 legs in series with your tank cap, so Zbranch is twice the value you calculated.

A more sensible prescription would be

Zbranch = Ztankcap

since it matches the source impedance to the tank cap impedance. But that leads basically to the resonance condition and not to a larger than resonance C. Larger than resonant C can only be explained by taking into account the discharging of the tank gap through the spark gap. That is much more involved than calculations based on impedances.

Sorry, I've been sloppy using Z. Z is a complex number. Here only its absolute value is meant.

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