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Re: [TCML] Charging a cap to 63% V

NST's can behave in unexpected ways with regard to power processed, vs.
applied voltage and capacitive load.  I performed an experiment to
determine the optimum capacitor value for 15/30 and 15/60 NST's, at 120V
and max Variac (~135V) input voltage.  The experiment
and results are documented at

While the optimum cap value is less than definitive, one thing is certain.
 Running at a Variac-elevated primary voltage produces a
dramatic increase in processed power.  Further, using a LTR cap value,
particularly at elevated primary voltages, results in far higher charging
currents than indicated by the NST faceplate rating.  I measured the actual
RMS power throughput to the cap from a 15/60 at max Variac, as 939 Watts.
 Bear in mind that this figure is the real power - gap and transformer
losses are excluded from this figure.  So *IF* there were no gap or
transformer losses, the 15kV NST would be charging the cap at an RMS
current of 62.6mA.  Given that actual gap and NST losses are considerable
(I wish I had an actual number...), the actual charging current is FAR
higher than 62 mA.

The short answer is, always run with the Variac set to "11".

Regards, Gary Lau

On Mon, Mar 19, 2012 at 9:04 AM, jeff mill <jeffmill2@xxxxxxxxxxx> wrote:

> The reason why I ask this is that I want to get as much out of my nts's as
> possible. With them just sitting there shorting the output they pull around
> 18.5 amps @ 120v. When connected to the TC, which has around a 64nf tank
> cap and run it , it also pulls around 18.5 amp @120v. So can I assume I am
> maxed out on the capabilities of the nts's as far as getting the most out
> of them ? T map says the ideal for a rotary is 161nf but wow I don't think
> I can get anymore out of my nts's. I know that in the real world they
> cannot output 210ma @ 9000v  and I think T map does . Am I correct on this.
> If so in reality what could I estimate the output of the nts's to be, maybe
> 210ma @ 4500v. Does Tmap take 8.33ms ,210ma and V (9000) and come up with
> the cap size ?
> -----Original Message----- From: Grenadier
> Sent: Sunday, March 18, 2012 11:44 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Charging a cap to 63% V
> impedance * capacitance
> On Sun, Mar 18, 2012 at 9:59 PM, jeff mill <jeffmill2@xxxxxxxxxxx> wrote:
>  Say I have 4 nts’s paralled with a total output of 9000v @ 210ma rating.
>> What is the formula to calculate the charge time of a cap in this current
>> limited situation.
>> Thx JM
>> ______________________________**_________________
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