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# ballast Inductor Choke coil (fwd)

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From:  David [SMTP:davmckin-at-ix-dot-netcom-dot-com]
Sent:  Saturday, April 04, 1998 2:25 AM
To:  Tesla List
Subject:  Re: ballast Inductor Choke coil (fwd)

Tesla List wrote:
>
> ----------
> From:  ESchulz531 [SMTP:ESchulz531-at-aol-dot-com]
> Sent:  Friday, April 03, 1998 5:39 PM
> To:  tesla-at-pupman-dot-com
> Subject:  Re: ballast Inductor Choke coil (fwd)
>
> WHAT,
>
>     N = SQRT (38200 * ((9 * 3) + (10 * 12))/3 * 3)
>
> Then:
>
>     N = 1475 turns would be required
>
> Sorry but you are wrong it is 789.895
>
> But you are right about the coil, anybody know the equation for a multilayer
> cylinder coil?
>
> Erik

Dear Erik & All,

The Multilayer Air Core Inductance formula is:

31.6 * N^2 * r1^2
L {uH}  =   --------------------------
6*r1 + 9*L + 10*(r2-r1)

L{uH} = Inductance in microHenries
N^2   = Total Number of turns on coil Squared
r1    = Radius of the inside of the coil {meters}
r2    = Radius of the outside of the coil {meters}
L     = Length of the coil {meters}

Note the similarity to the formula for the single layer
air core coil.  Hope this helps everyone.

David L. McKinnon

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