[Prev][Next][Index][Thread]

# Quarter Wave Calculations, HELP!!!

```
----------
From:  Andrew Chin [SMTP:chinny-at-ozemail-dot-com.au]
Sent:  Friday, April 17, 1998 11:13 AM
To:  'Tesla List'
Subject:  RE: Quarter Wave Calculations, HELP!!!

Sorry bout the carriage return.  The word wrap gives
me the impression that it will send like that.  Oh well.

Could you please tell me Wheeler's L formula?  I already
know Medhurst's C formula.

I missed that point about the correct topload bit in my
explanation.  So did I miss something in my reasoning?

I myself thought that this formula was way too simple but
I had no other way to prove it other than plugging values
into various Tesla Coil design programs.  By doing so I
found that this method was fine.

With that formula confirmed, I then used the formula

F = 1/[2pisqrt(LC)]

Where the inductance of a single layer air core coil is
calculated using

L = N^2.r^2/[254(0.9r+l)]

Where 	L = inductance in mH
N = number of turns
l = coil length in mm
r = coil radius in mm

Solving for C would give me the total capacitance of the
secondary circuit required for resonance.  So I used
Medhurst's C equation to find the self C of the coil.  I
subtracted this from the total C and this got me the required
C for the top load.

Now all these were confirmed using other values plugged
into other design programs and gave me the same answers
(within 3 decimals.)

Could I have made a fluke?

PS I hope this time the hard returns made it in.

-----Original Message-----
From:	Tesla List [SMTP:tesla-at-pupman-dot-com]
Sent:	Friday, April 17, 1998 1:57 PM
To:	'Tesla List'
Subject:	Quarter Wave Calculations, HELP!!!

----------
From:  Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent:  Thursday, April 16, 1998 2:38 PM
To:  Tesla List
Subject:  Re: Quarter Wave Calculations, HELP!!!

Hi Andrew,
First off, would you please insert the odd carriage
return. Ireceived your message truncated to a single line of ???
characters.

> From:  Andrew Chin [SMTP:chinny-at-ozemail-dot-com.au]
> Sent:  Wednesday, April 15, 1998 2:22 PM
> To:  'Tesla List'
> Subject:  RE: Quarter Wave Calculations, HELP!!!
>

> I simply used a physics formula Frequency = Speed of light /
> Wavelength.  In the case of a quarter wavelength tesla coil, the
> wavelength in this case would be 4 times the length of wire used
> to wind

The length of wire won't correspond with the coil self-F like that
i.e. a bare resonator will never resonate at a frequency such that
the wire is 1/4 wavelength long in it. You can do it by adding the
correct amount of Ctop but I haven't yet seen any good reason to do
so (other than providing some top energy storage). If you don't
believe me, measure all of your resonators without a topload. Just
use Wheeler's L formula and Medhurst's C formula to predict your
coil's frequency.

Malcolm

```