# Re: power vs. toroid size

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• Subject: Re: power vs. toroid size
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• Date: Tue, 05 Apr 2005 08:21:31 -0600
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`Original poster: "Gerald  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>`

`Hi Skip,`

There are several ways to approach the problem. One way is to start with your power source and sparkgap type (static or SRSG). Note I have no experience with ARSG so I wont comment about them. With NST's , it is common to run LTR where (60Hz line) Cp = 1.6*Cres for a static gap and a Cp = 2.8*Cres for a sync RSG and the breakrate is 120.

`Cres (nf) = 10^9/(2*pi*60Hz*XL)`

XL = Vs_oc/Is_ss (assumes all of the transformer impedance is inductive - good assumption for NST's)

In my system using two 15KV 30ma NST's and a SRSG, the VA rating is 900VA and the measured wall power (real) was 1080 watts. Pig powered systems are often run smaller than resonance and larger breakrates are used. If you use a static gap, you can figure on about haft the VA rating for real power.

Once your Cp and secondary size are chosen, you can plot the topload voltage vs toroid size using tools like JAVATC (the program uses conservation of energy and assumes no losses) . This will probably be the "best" topload voltage you could get before breakout. As the toroid size increases, the effective topload capacitance increases and the topload voltage goes down. On the same plot, superimpose the breakout voltage vs toroid size. This voltage will go up as the toroid size increases. Where the two curves cross is probably the largest toroid you should use. If, by chance, your toroid does not breakout, you can always add a breakout point (thumb tack or roofing nail) to the toroid. Antonio has a field program that calculates the breakout voltage for various geometries of rotation. As a reference, the program predicted a 500KV breakout voltage for a 6x24 inch toroid. This voltage will scale linearly with toroids of different sizes sharing the same aspect ratio. A 12x48 inch toroid, for example, would have a breakout voltage of 1MV.

`This method work just fine for me.`

`Gerry R.`

`Original poster: Skip Greiner <sgreiner@xxxxxxxxx>`

I suspect that this subject may have been discussed before but I have been unable to locate info in the archives.
Has work been done to determine the minimum power input to a TC to drive a given sized toroid to breakout? I under stand that there are many factors that might affect breakout including the roughness of the toroid surface, humidity, etc. But I would think that, assuming some reasonable efficiency, there should be some relational ship between power input and the ability to get breakout from the toroid. I would think that when designing a new TC, one would have to take into consideration the possible sizes for the toroid when setting the parameters for the secondary. Any comments would be appreciated.
Skip