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Re: Reactance
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> From: Tesla List <tesla-at-poodle.pupman-dot-com>
> To: Tesla-list-subscribers-at-poodle.pupman-dot-com
> Subject: Reactance
> Date: Sunday, February 02, 1997 12:10 AM
>
> Subscriber: Rodney.Davies-at-anu.edu.au Sat Feb 1 21:56:48 1997
> Date: Sun, 2 Feb 1997 04:18:04 +1100 (EST)
> From: Rodney Graham Davies <Rodney.Davies-at-anu.edu.au>
> To: tesla-at-pupman-dot-com
> Subject: Reactance
>
> Hi All,
>
> After reading through some extremely helpful documentation here on the
> list, I've found some formulas and concepts I've been looking for...
> Thank you too all contributing! Much appreciated and helpful!
>
> Ok, well, I'm just trying to make sure I've got a firm grasp on tuning
> and the primary LC circuit.
> As I understand, the inductive reactance in the primary has to be
> cancelled out by the capacitive reactance of the capacitors.
> Now I've got the formulas for calculating the I.R. of the primary, and
> the capacitors -
>
> X = 1/(2*Pi*F*L) for inductive reactance, where
> X is on ohms
> F is in Hz
> L is in Henries
>
> X = 1/2(2*Pi*F*C) for capacitive reactance, where
> X is on ohms
> F is in Hz
> L is in Henries
>
HERE'S YOUR ERROR! X=2*Pi*F*L for inductive reactance
Also, F here is the RESONANT Frequency you want, NOT 50Hz!!
> Am I doing alright so far?
>
> Ok, now, if the inductance of the primary coil is known, and the value of
> the capacitor(s) is known, how do you get these formulas to work out as
> to find the resonant frequency of the known series LC circuit?
>
> Ok, Scenario -
>
> Capacitors - 0.1uF -at- 50KVDC (Pulse type)
> Primary "Flat Pancake Archimedes" -
> - 5 turns 3/8" Cu Pipe
> - spacing 1" from turn-to-turn
>
> |<--------- 5.75" ------->|
> _ _ _ _ _
> -(_)---(_)---(_)---(_)---(_)- <-------primary coil
> | | |<-1"->|
> ^---- 3/8"
>
> - Outside Diameter 26.5"
> - Inside Diameter 7.5"
> - Width = 5.75"
>
> Anyway, using the formula -
>
> L = R^2 * N^2 / (8*R + W)
>
> where, L = uH
> R = average radius
> N = # of turns
>
> I get a calculation of 18.40 uH. I think I did it right.
>
> Ok, now we know L for the primary.
> Next, calculate L-Reactance -
>
> XL = 1/( 2*Pi*50*18.40*10^(-6) )
> where F = 50 Hz (Australian Frequency)
>
> = 696.5 Ohms
>
HERE'S YOUR ERROR! XL=2*Pi*F*L not the reciprocal as you used.
Also, F here is the RESONANT Frequency you want, NOT 50Hz!! Try using
140Khz instead.
> * * * * * * * * * * * * * * * * * * * * *
>
> This is probably where I'm stuffing up as F should be the frequency at
> which the C-Reactance cancels the L-Reactance...???
>
> Should I be working backwards from the known self-resontant frequency of
> the secondary-coil and plug that value into the equation to work out what
> sort of capacitors I need for this particular primary and secondary coil?
> (Using the C&L Reactance equations)
>
YES! The resonant frequency of the SECONDARY is the prime item to be
using!!!
The 50Hz resonant thing with the neon transformer boils down to this: It
is NICE to match the power input stuff, but NOT ABSOLUTELY NECESSARY!
A good rule of thumb with a 30 ma neon is to use .005mfd for every 15KV of
neon voltage. So a 60 ma 12KV neon would use (60/30)*.005*(12/15)
This is just a guideline. MANY coilers use MUCH larger capacitance values.
> Self-resontant frequency for my secondary (with toroid) is about 140 khz.
>
> I may seem a little academic trying to calculate everything, but I've
> found that by doing this during design helps to give me an idea on how to
> build the coil. Yeah, sometimes the calculated values are out from actual
> measured values, but most of the time the margin of error is around
5-10%.
>
> Basically, the way I follow things is try to think of how many volts you
> want, and build a secondary close to size. Playing the guessing game
> here, but from passed experiences it's not so much of a guess anymore.
> Ok, from there, then measure the resontant freq.
>
> Next, design a primary coil, and try and get a near match of capacitors
> simultaneously. This is where the nice hairy equations and math comes in.
>
> Ok, concepts here -
> 1) Minimize reactance in the primary.
> 2) Find capacitor value to do so. (For series LC circuit)
> 3) Hope to buggery the value of the frequency is that of the secondary.
>
> Am I doing alright again?
Nope. 1) design secondary height, diameter, wire size.
2) calculate self-resonant frequency using hairy formulae.
3) build secondary
4) measure ACTUAL self-resonant frequency. Use THIS value in all
subsequent equations. (unless you do steps #5 & #6)
5) make toroid if desired
6) place toroid on secondary and measure ACTUAL resonant frequency.
Use THIS value in all subsequent equations.
7) design/build 14 turn flat spiral primary. ASSUME TAP at tenth turn.
USE the Tenth Turn inductance value as your working Inductance.
-or- design other type of primary if desired. 80% point is your
operational tap and initial calculation point for inductance.
This gives us tuning room for later!
8) calculate capacitance needed for resonance at tap ten such that
both the primary and secondary circuits have the same resonant
frequency. Build it and measure it if possible.
9) determine number of milliamps required from neon using approximation
formula:
10) Add enough neons to ensure that you have enough milliamp capability.
It is better to have too much current than not enough.
11) calculate any Power Correction Factor capacitance to be added to
the primary of the neon transformer to enhance performance.
12) Add in all RF chokes/bypass capacitors/safety gap, etc.
13) Build a DECENT spark gap, such as the Richard Quick Air Cooled Quench
14) wire it using good RF wiring techniques
15) make sure you have a really good RF ground
16) Wire AC mains circuitry
17) make sure all other electronic equipment is unplugged and out of way
18) make sure no modems or any thing else is wired in to any computer
19) double check wiring. Is primary tap on? Is your secondary grounded???
20) make sure spark gap is properly adjusted (if adjustable)for initial
close spacing.
21) plug it in
22) turn it on
12) Tune it for maximum output
13) Have fun!
>
> Well, even if the values come close, the primary is tunable, but one
> hopes the values are close to begin with.
>
> Does anyone use similar approaches to strict coil design?
>
> My main idea behind all of this is that I extremely interested in the
> mathematical/physics work behind the design of TC's.
> I hope I have my concepts around the right way...
>
> Oh well, we'll wait and see then!
>
> Suggestions, flames, formulas, ideas, concepts, designs, whatever are all
> welcome!
>
> Thanks for your help guys!
>
> Catchya later!
>
> Rodney
>
>
> -- 'what is the average air-speed of an electron?'
> 'Erm, European or African electron?'
> 'what?! I don't know that....<crash, bang> Whaaaaaa! ... <thud!>'
Rodney,
I hope the above remarks help you. The process is not too bad, but it does
help to have it all written down so that we can see the typical sequence. I
say typical, because there is no strict sequence. This is just the one that
seems to me to best arrive at a working coil in the shortest time.
Fr. Tom McGahee