[Prev][Next][Index][Thread]

Re: Power in a TC System

Hi Gavin,

At 11:17 PM 05/19/2000 +0100, you wrote:
>Hi John,
>I know a bit about coiling, but tend to get lost with definitions (I only 
>learnt
>the other day what an MMC was, but had been using them for the last few 
>years!).
>

Really!  The first use of today's modern MMCs with high current
polypropylene caps has been credited to Reinhard in the summer of 1998, so
far...  We are kind of wondering who was the first to use them?  Not that
there is any great pot of gold for being the "first" but if you have used
them before all of us you should get some kind of honorable mention...
Other mini caps have been used for a decade plus but only the modern poly
caps have really worked well.

>A matched primary capacitor? Is this when the capacitors impedance matches 
>the NST
>secondary's at the line frequency, i.e. forms a resonant circuit?

This is referred to as a "resonant matched primary capacitor value".  The
impedance of the cap at 60Hz cancels the output impedance of the NST. 

>
>What is LTR? Is this when the impedance of the primary capacitor loads the 
>NST to
>it's maximum power capacity:-
>
>Xc = Vout / Imax

LTR is really any value above the resonant capacitor size.  You can charge
capacitors larger than the resonant value to the full NST rated voltage
easily.  This gives you greater stored energy (but perhaps a lower BPS).
This is around 1.5 times the resonant value.  With a rotary sync gap, you
can go further still.  My 15/60 NST uses 28nF and my 9/30 NST uses 24nF.
Far above the 10.6nF and 8.8nF resonant values.  With a static gap, my
15/60 NST used 17nF.

>
>Sorry for these elementary questions, but I have got to know some time!

Sure!

Cheers,

	Terry
 

>
>Thanks for your help,
>
>Gavin.
>
>Tesla List wrote:
>
>> Gavin,
>>
>> Using the standard formula to obtain a "matched" size cap for a
>> 12/30 NST gives about 0.006uF.  This particular size cap does seem
>> to "neutralize" the NST's leakage reactance and permits a lot of
>> current to be drawn.  My 12/30 NST drew 620 watts (as measured
>> with a wattmeter) with that sized cap, and the VA was about the
>> same when I used PFC.  Although I used a similar sized cap for
>> a few years in my coil with no trouble, some folks on the list
>> questioned the wisdom of letting the resonant voltage build up
>> so high, and they advocated used a larger (LTR) sized cap.  The
>> LTR sized cap draws about the same input power as far as I can
>> tell, and gives the same spark length for a given power input,
>> although I do use a 140V step up type variac.  One test that I did
>> seemed to show that a NST can draw more than its rated power
>> only with a matched sized cap, if the step up variac is not used
>> (I'd have to check my notes to be sure).  In any case, I'd say that
>> the use of this LTR sized cap is simply to keep the voltage lower to
>> protect the NST.  Inductive kick charging permits the NST to
>> deliver a good amount of power to an LTR cap.  If you use a non-
>> shunted transformer such as a pole pig, these can use a larger
>> than expected capacitor because a pig can deliver a lot more power
>> than it's rated for.  In addition the external ballast can be adjusted for
>> various capacitor sizes.
>>
>>
>> Cheers,
>> John Freau
>>
>
>
>
References: