# FW: Corrected definition of pancake R (formula OK)

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From:  SBJohnston-at-aol-dot-com [SMTP:SBJohnston-at-aol-dot-com]
Sent:  Tuesday, February 17, 1998 11:23 AM
To:  aerpel-at-op-dot-net; tesla-at-pupman-dot-com
Subject:  Corrected definition of pancake R (formula OK)

Alfred (aerpel-at-op-dot-net) wrote:

>Below is the body of a post I can't get onto the Tesla list
>because my email is screwed up, so you might not see it right
>either.  You were given incorrect information for pancake
>primary inductance calculation.

Yes... your email is looking a bit strange.  Lots of control characters and
stuff like:    +AHw-.   I'll post your comment to this list for you...

Alfred wrote:

>R is from the center of the pancake to the center of the
>windings.  This will only equal A/2 by accident.

I cannot make out your ASCII drawing, Alfred, but here's a copy of Bert's
orginal drawing...

Center
Line
|
O 0 0 0 0 0 0 0     |     0 0 0 0 0 0 0 O
|
|<----------------->|<--->|
a             b

a = outer radius at turn "N" (inches)
N = turn number
R = Ave. Radius = (a+b)/2
W = coil width at turn "N" = a-b

L = (R^2 )*(N^2)/(8*R + 11*W) in MicroHenries

Alfred, if I understand correctly you're saying the dimension R should be the
average radius of the windings -- but the formula should be like this...

Center
Line
|
O 0 0 0 0 0 0 0     |     0 0 0 0 0 0 0 O
|
|<----------->|
R      |
|<----------------->|<--->|
a            b

If this big headache of mine is not blocking my algebra, your definition of R
would be...     R = [(a-b)/2]+b
...right?

Steve Johnston

sbjohnston-at-aol-dot-com

PS -- do you think it would help a headache to ground my body and use my
Tesla Coil to send a few strikes into my head???  Not that I'm desperate or
anything... but, whew.

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