Re: the toroids size?
You can find the capacitance of your sec coil with the frequency equation.
You have three variables: frequency, inductance, and capacitance. You have
measured your freq and inductance, so using these values just solve the
equation for capacitance and plug in your values. The result will be your
sec coil capacitance (self-capacitance). This is increased only slightly
by your environment, so be sure to elevate the sec coil approx 12 to 16
inches off any ground plane object such as a table or concrete, etc.
You now the the calculated cap together with your measured toroid cap for
the final value of total system cap.
With a primary cap of around .02 MFD and 120 ma of driving (charging
current) in the range of 9 to 15 kV you will have a nice output spark.
When you first set up your primary use lots of turns (16-20) of scrap wire,
and then after tuning, replace with nice-looking and more efficient copper
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: the toroids size?
> Date: Tuesday, January 05, 1999 9:37 PM
> Original Poster: Finn Hammer <f-hammer-at-post5.tele.dk>
> I have now finished rolling the secondary for my coil, and I setteled
> for a polypropylene former, 7 inches dia, with 900 turns of wire, 0.75
> mm dia. That`s in between 20 and 21 AWG. 19.4 ohms DCR
> Aspect ratio is 1:4,1 .
> Tesla coil cad predicts 31.3 mH, and I have measured 31.4mH
> Self cap: 13.54, I don`t know how to measure picofarads.
> The resulting resonant frequency is approx. 244 kHz and the quarter
> wawelength resonant frequency is 147 kHz. This is met with a topload of
> 23.73 pF.
> Question is:
> Should I proceed to make a 1/4 wawe resonator out of this coil, ie.
> stick with the 23 pF, or is it ok to go higher, like 30pF for example?
> I admit to designing this coil, at least to some extent, according to
> how it looks. Does it look harmonic? I think that a toroid slightly
> bigger in diametre than the secondary coil itself, and slightly smaller
> in OD, than the primary, (which in turn has a diametre equal to the sec.
> coil hight.) makes the whole unit look good.
> Nice, fat toroid.
> Such a toroid would be 8" Dia. allu. duct. 20" center to center dia.
> and be 31.15 pF. Allow more primary turns in use, all else equal.
> I will, in due time, have 3 kVA to pour into the thing.
> Cheers, Finn ( getting closer to sparking time )