[TCML] primary-secondary tuning
bunnikillr at cox.net
Thu Sep 10 19:37:35 MDT 2009
Wintesla is a good tool to start with but I have found that JAVATC is
very good at producing more information that is useful to design a Tesla
Since you have built your secondary, and I suppose you already have a
toroid, you have now set the scene to have a need to design your primary
and cap system.
Once you have built your secondary, you have set a frequency for the
coil, ( the 430.78KHz) add a toroid to it and the frequency of the
combo drops... ( in your case 230.61 KHz)...
Now you need to design a primary that will oscilate at 230.61 KHz. This
will depend upon the capacitor you plan to use... since you are going
with a 15KV 30mA unit, a cap in the 30+ KV range is a good start ( I
prefer 40KV rating). WinTesla will give you a cap rating that is
resonate to the transformer for "best" results... only problem is that
the "best" results IS resonate to the transformer and that can mean
certian death for an NST. Go for a capacitor that has a larger than
resonate value in capacitance. WinTesla told me that you would see a
rating for .0053 uF for a 15KV @30mA unit ( remember that is resonate)
bump it up to .01 uF @ 30+KV.
Since you plan to use 1/4" Cu tubing, space the tubing 1/2" apart (
center of tube to center of tube... or 1/4" gap between tubes). Plan on
approximately 15 turns with a tune point at somewhere near 11 turns...
the tune point is not exact... depending on how much wire length you
have between the cap and primary will "mess" with the tune point of your
To answer your question on the corellation between the primary/cap setup
and the secondary/toroid setup....
The primary and power cap work in combination when the spark gap
conducts to produce an oscillation of what ever Hz ( depends upon the
size of cap and number of turns of the primary.. along with other
variables.... ) to produce a sinusoidal wave that "pulses" back and
forth between the cap and coil until the resistances of the coil and cap
eventually weaken the "wave action" to where the gap no longer can
conduct. This so called wave action has to have the same pulse rate as
the secondary/toroid combo to recieve and build up voltage in the
secondary/toroid combo. Basically, the primary/cap combo produces a
field that is imposed upon the secondary/toroid thru induction to excite
the secondary/toroid to a voltage which can be increased to create
streamers... ( that is another complete chapter in this story).
As far as spark gap length ( width), the width of the gap determines
when the cap has enough voltage in it to ionize the air between the gaps
to produce a conductive arc. For 15KV, the maximum gap width should be
approximately .3 inches total ( if using multiple gaps, divide .3 by the
number of gaps in the multigap system for each gap width). To be on the
safe side, don't go much beyond .285" width... this should set the gap
firing voltage to about 13,500 V. If you are using a safety gap ( highly
advised) set it to .3 - .290 of an inch width. Another thing to
consider is the type of gap geometry to employ... spherical ( copper or
brass balls approximately 1" dia for the safety gap or 1" dia copper
tubes will give you the best results in controlling the distance/arc
Since you have a set parameter of the secondary/toroid, primary voltage
supply, the only two things left to change easily is the capacitor value
or the tune point on the primary. The easier of the two things to change
is the tap point of the primary as compared to the capacitor value.
Sooooo... stay with the secondary size, toroid size, voltage output,
and cap size. Adjust the primary tap point...
and remember.... Tesla coils never work the first time you fire them
up... dont be dissapointed, try a new tap point ( considering that you
wired everything up properly ;)~....
hope this helped...
Brian Hall wrote:
>I am coming along nicely with the design of my TC, and am using WinTesla to help with the calculations.
>One thing I am not sure of is how the secondary KHz and topload capacitance relates to the tank capacitor/sg and where to tap the primary.
>Numbers given to me on WinTesla's secondary coil (which I already made) are:
>Frequency: 430.78 KHz
>1/4 wave: 571.21 ft
>Frequency: 230.61 KHz (why does it list frequency twice? is this the 1/4 wave freq?)
>w/Topload C of: 17.67 pf
>so - how do those numbers (or which of them) tell me what the resonant frequency should be for the primary?
>I am choosing a flat archemidies spiral from 1/4" copper tubing but want to know what length/spacing I will need and where abouts to tap it - so that I can get it in tune without an oscilliscope. Some easier to understand way of plugging in the numbers and getting out whatever the matching frequency should be to resonate with the secondary.
>I will be running it off a 15kv/30ma NST, so it sounds like i will need about 30kv for the tank cap, right? How much does the microfarad rating of the tank cap have to do with the primary frequency, as compared to the spark gap length? I don't have an oscilliscope so I want to get the numbers right for best performance.
>And since radio shack has discontinued their power conditioners (to prevent backfeed into your house) does anyone else know where to get them? the NST as you can tell runs at 450 watts max so .. like a reverse surge protector? protects from surges coming into the appliance as opposed to out from the wall socket
>Get back to school stuff for them and cashback for you.
>Tesla mailing list
>Tesla at www.pupman.com
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