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Re: [TCML] Primary selfC



Hi Bart,

6.4nF sounds more than I thought :S in fact if this is the case I could just re-work my primary to give 3nF in SelfC and not even have to bother having the tank/tuning cap..

Would it be possible to add your formula into your flat primary strap calculator ?

I am not sure about the effects of the secodnary on my primary... K is about 0.05K so hopefully it will have have too much effect... though I need to get some ballpark figure with the primary itself before I can start to worry about other factors...

I will assume that the primary SelfC will increase when the secodnary is inserted ? If it works out a ballpark of 1nF for example, then I will re-work my primary to say 2nF....

Chris




----- Original Message ----- From: "bartb" <bartb@xxxxxxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Friday, July 25, 2008 2:45 AM
Subject: Re: [TCML] Primary selfC


Hi Paul, Chris,

It might be more accurate to look at the total length of the ribbon and width to determine area and treat it as rolled capacitor separated by 1mm, using air as the dielectric, and determine C as one would with any flat plate capacitor, but in this case, as a "rolled capacitor".

C = 0.2248*k*A*(N-1)/(d*x)  (in pF)
   where
    k = Dielectric constant (1.0006 for air)
    A = Effective plate area in square inches (length x width)
    N = Number of conductive plates (3 for a rolled cap)
    d = individual dielectric film thickness (.03937" in this case)
x = number of stacked sheets of dielectric between plates (1 in this case)

I think Chris is looking at about 6.4nF for the ribbon primary. So he's probably correct to ask the question given the very low tank capacitance. Primary C may be much higher than expected (a good deal of area at about 557 square inches). Should be able to verify by inserting a signal to the primary as one would with a secondary and looking in the range of 470kHz assuming inductance is about 18uH.

Regards,
Bart

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