Re: Coil size to faraday cage size ratio

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>

Hi Finn,

At 12:30 PM 11/18/2004, you wrote:
>All,
>
>I`ve had my OLTC coil tested for EMI, and since it exceeds the legal limit 
>a 100 times, inside a faradays cage with 50db damping. This corresponds to 
>a 4Km (3miles)radius inside which the legal limit is violated.
>I am going to need a better cage.

Oh good!!  The EMI is not serious :o)))

Do you know if that was "conducted" or "radiated" or just blew up their 
meter :o))

Any spectral data as to exactly what frequencies my have slightly crept 
over the limit?

What standards were they using?  All kinds of equipment has to meter 
different standards and I doubt they had a Tesla coil standard which your 
shielded coil would have passed :o))


>Question: For the same coil, will a big faraday cage offer better damping 
>than a small one.
>My reasoning says yes, since the longer distance to the cage, in the case 
>of a big cage, will result in a weaker field than as in a small cage.
>If the coil produces 600kV and the distance to the cage is 1meter in the 
>small cage and 2 meters in the big cage, then the small cage has to damp 
>from 600kV/meter, whereas the big cage only sees 300kV/meter.

Probably a dual cage would be the next step.  But you have to be sure that 
stuff was not blasting out through the grounds or the cage it's self was 
not acting like an antenna.


>Is this correct?, and will it matter? If yes, by which factor 1/2? :-|
>1/4? :-\    1/16? ;-)

If the first cage dropped it -50dB then the second cage should drop it to 
-100 dB.  But that is assuming it is all working right.

Normally a good cage should drop the EMI vastly down.  But I am not sure if 
their standard was way to low or the cage is leaky.  "100 times" is only 20 
dB ;-))

Cheers,

         Terry



>Cheers, Finn Hammer
>
>
>