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Re: Self resonance of a coil
Tesla List wrote:
All,
I previously posted a formula for estimating self-resonance of a
secondary coil. Turns out the formula's OK, but I messed up on the
numerical portion in the example. This definately will make you're
mileage vary! Also, I found I "renamed" Harri Soumalainen to "Harry"!
Very sorry on both counts!
Guess its time to go sit on the coil!
-- Bert --
<SNIP>
> The best way is simply to measure the coil after you wind it using a
> signal generator and base-driving the secondary through a pair of
> back-to-back LED's. You can try the following empirical approximation
> for "what-if" designs. This is similar to a formula which may have
> originally come from Harry Soumalainen or Richard Quick, but has been
> adjusted for feet and inch measurements:
>
> F = 984,300/((3.485X)*(L/D)^-0.304) (KHz)
> Where:
> L = Length of Winding (inches)
> D = Diameter of the winding (inches)
> X = Physically computed Length of wire (feet)
> d = effective Wire diameter (including insulation and any spacing)
> But: X = Pi*D*L/12d feet
> and: n = L/d turns
>
> Example:
> L = 31"
> D = 10.25"
> d = 0.032" (21 AWG with Dual-Thermaleze)
>
> Then: X = 2599 feet
> n = 969 turns (close-wound)
>
> and: F = 984,300/((3.485*2599)*(31/10.25)^-.304)
> = 984,300/(9304)*(3.024^-.304)
> = 984,300/6646
> = 148 kHz
>
> Since this is an approximation, your mileage may vary. On a sample of
> two coils I tested, it was within +/- 5%. Enjoy.
>
> -- Bert --