[Prev][Next][Index][Thread]
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
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
* * * * * * * * * * * * * * * * * * * * *
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)
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?
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!>'