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Re: Barts Coil Desing (was flashing vs. whatever)
From: Bert Hickman[SMTP:bert.hickman-at-aquila-dot-com]
Reply To: bert.hickman-at-aquila-dot-com
Sent: Saturday, November 29, 1997 12:43 AM
To: Tesla List
Subject: Re: Barts Coil Desing (was flashing vs. whatever)
Tesla List wrote:
>
> From: Barton B. Anderson[SMTP:mopar-at-mn.uswest-dot-net]
> Sent: Thursday, November 27, 1997 7:15 PM
> To: Tesla List
> Subject: Re: Barts Coil Desing (was flashing vs. whatever)
>
<SNIP>
> > I suspect that because of the problems you had in estimating too low an
> > operating frequency, this also caused you to need an abnormally high
> > tank cap value. To bring your system into tune, you'll only need a bit
> > over 0.05 uF. I'd also recommend adding a few more turns to your primary
> > to give you a bit more tuning range.
> >
>
> Bert, Malcolm, All,Here, I run into a conflict. When I calculate the cap off of
> transformer impedance matching for 60Hz, I come up with 0.256uF.14.4KV x .707 =
> 10,181Vrms
> 10KVA / 10,181Vrms = 982mA
> 10,181Vrms / 982mA = 10,368ohms
>
> C = 1/(2pi x Z x F)
> C = 1/(6.28 x 10,368 x 60Hz)
> C = 0.256uF
>
> However, if I design off the resonator specs, I come up with 0.05uF as the cap of
> choice (using Ed Sondermans Excel spreadsheet). Here's where I need come
> clarification. I know I can swap C for L to keeping mutual reactance the same
> lowering my cap value, which is what Malcolm is suggesting, and may very well be
> what I end up doing. But what of the capacitor matching to the line frequency? Is
> this all hogwash or did I just make some wrong assumptions?
NOW I understand the source of the discrepency! It is essential that
your tank cap and primary be tuned to your secondary/toroid's operating
frequency. Now, for maximum power output you may also choose to "size"
the tank cap to the transformer/ballast power delivery capability.
However, you must STILL keep the system in tune. BTW, the 14.4 KV term
in the above equation is already RMS volts, so it does not need to be
derated by 0.707. This results in a properly "sized" cap value of about
0.128 uF to match 10 KVA. However, you can easily run the pig
intermittently at 20 KVA which will bring you up to the 0.256 uF cap
previously computed.
However, when you increase the size of the tank cap, you also directly
increase the amount of energy per "bang". Going from 0.05 uF to 0.256 uF
basically quintuples the energy available when the gap fires. For
example, if your gap fires at 16 KV, you'll have 6.4 Joules of energy
per bang with a 0.05 uF cap, but a whopping 32.7 Joules with the 0.256
uF cap. All other things being the same, the output voltage of the coil
would also increase by a factor of about SQRT(5) or 2.24 times...
<SNIP>
> <(SNIP from Malcolm)
> >Whoa!! IMHO your secondary is *far too short* for the voltage that
> >your primary energy will develop in it!!! Go for a *much* smaller cap
> >and higher primary inductance. I wouldn't build a secondary less
> >than ten feet high for that cap value. I might be shot down in flames
> >by coilers who have built such high energy coils but I'm placing my
> >bets.
> >> What size toroid are you contemplating using?
>
> Malcolm, as mentioned, the toroid is 8 x 30. Interesting point though on the size of
> the secondary for the "POWER" of this coil as based on the cap size of .256uF. It's
> interesting to me because I have ran across articles identifying to stay away from
> long narrow forms. Also, to consider the ratio of primary to secondary depending on
> the type of primary in use. And with flat pancake primary's, the ratio between the
> two should be near 1:1. My ratio is 1.5:1 which I felt was a pretty good one. Maybe
> not?
>
Malcolm is absolutely correct - this size tank cap WILL undoubtedly
overvolt your 33" high coil. You'll need to "scale up" the secondary
coilform height, diameter, and wire diameter by at least a factor of 2-3
to withstand the higher voltage stress and keep the number of turns
similar as before. The toroid size will also need to scale upwards to
increase both the breakout voltage and top-load capacitance. Doubling
the height and diameter of the coilform and using #12 AWG would be about
right. The toroid should scale to perhaps 60" x 12", with the
combination having an operating frequency of around 50 kHz. This would
"tune" at about turn 5 on your primary. However, your spark gap needs to
be able to handle 1500 Amp peaks, and you may need to go to 0.5" or
0.75" copper tubing on the primary. You'll also need a very robust RF
grounding system.
<SNIP>
>
> Heat wave in MN (40+),
> Bart
Safe coilin' to you, Bart!
-- Bert H --