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Re: Calculating Sec. Voltage
Rodney Graham Davies wrote:
> I'm searching for some formulas that may give results close to actual
> values, when calculating the secondary's output voltage.
>
> For now, I've been using a silly little formula I retrieved from my old
> high school physics book which is an ideal (I mean for an "ideal"
> xformer) equation -
>
> Vs Vp Ip
> -- = -- = --
> Ns Np Is
[snip]
> Now, I've applied this formula to a known coil (Yup, the Super Model 9
> from Bill Wysock, yet again...fine coil system too I might add!)..
>
> Ok, specs -
> Ns = 800
> Np = 4.5
> Vp = 20,000v
>
> So, Vs = 800 x 20000
> -----------
> 4.5
> = 3,555,555.556 volts
>
> The coil is actually noted in the gallery (Questacon Nat. Sci. & Tech.
> Centre, Canberra) as being a 3.5 MV coil...
> Although, most of the time it's only running on about 103v on the
> primary of the xformer as apposed to 250v.
>
> Well, this formula is a little too "easy" so to speak, so does anyone
> have any formulas, preferably of the "hairy" type which one could use for
> this problem?
A hairy equation is not required, if you apply the Conservation of Energy
to this problem.
The energy that ends up the secondary capacitance (Csec) is simply equal to
the initial energy in the Cpri, times the efficiency of the coil system.
So given:
Epri = 0.5CpriVpri^2
Esec = 0.5CsecVsec^2
and a typical coil efficiency of 50%,
Vsec = SQRT(0.5Cpri/Csec) x Vpri.
If you run some actual numbers, it may seem that this equation yields results
for Vsec that are far too low. But remember that the Tesla Coil arc dynamics
allow for streamers that are much longer than 20kV/cm would suggest.
The 3.5MV claim listed above is merely specsmanship, and blatantly violates
the Conservation of Energy. Perhaps it was (erroneously) calculated using
the standard dielectric breakdown strength of air.
-GL