RE: Practical limit to number of turns on primary ? ? ?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "John H. Couture by way of Terry Fritz <teslalist-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>


Dan -

I'm not sure I understand what you mean by constant source and primary
capacitor. Do you mean the power transformer like a 15 KV 60 ma NST would be
constant? If this is correct you can use the JHCTES Ver 3.3 computer program
for calcs using a constant power source. The primary capacitor is an input
and can be made any size you wish for a constant.

With the default secondary parameters the program automatically finds the
proper number of primary turns (9.98) for the system to be in tune. You can
change the number of primary turns by changing any of the secondary inputs
of the program.

To my knowledge there are no programs to find the efficiencies for TC
systems. However, there are many possibilities when TC  efficiencies are
involved and here is one of them. In general the efficiency in the primary
or secondary circuit of the TC system can be found by the equation
     J = .5 C x V^2

For the Ver 3.3 example we have
     J = 900W/120bks = 7.5 joules per bang input
     Cp = .02 uf   Vp = 15000 V RMS = 21000 V peak
     J = 4.41 joules

The efficiency at the primary capacitor
   Eff = energy out/energy in = 4.41/7.5 = .588 = 58.8%

If the losses are 41.2% the .02 uf capacitor would give the optimum
efficiency for the primary circuit. If this capacitor is reduced or
increased the capacitor would not be matched to the input energy and the
efficiency would be less than optimum (similar to the tuning) This is
because the capacitor would be charged to the pri voltage too soon or too
late in the cycle causing increased losses. You can see this if you make the
proper graph showing these three capacitor charging curves.

The above calcs will give you the maximum utilisation of the available
energy from the power source in charging the pri capacitor. You can keep the
pri cap constant and can change the number of primary turns and resonant
frequency by changing the secondary inputs of the program. You will then
have to do the calcs for the new efficiency.

Note that series impedance losses and coupling do not enter into these
calcs. However, it is obvious there is a lot more involved to finish the
job. Note that the optimum efficiencies for both the primary and secondary
circuits would give the maximum spark length and the best overall
efficiency.

  The main problem is to determine the exact input watt-second energy needed
to create the extra long random spark length. In other words the longer
output spark means the coiler has found a better overall efficiency for his
TC system. But how do you find the true input energy for that particular
spark (input J above)? And how do you find the true losses? Terry and a few
coilers have done tests along these lines. But more tests are required.

The JHCTES Ver 3.3 program can be found by clicking

     http://www.mgte-dot-com

Click on TESLA, then JHCTES (books)
At bottom of book page click on JHCTES Ver 3.3 for online program or
download the program. Click "Calculate" when changes are made.

John Couture

---------------------------------------


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Wednesday, January 29, 2003 10:00 AM
To: tesla-at-pupman-dot-com
Subject: RE: Practical limit to number of turns on primary ? ? ?


Original poster: "Mccauley, Daniel H by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>



Thanks for the response.  But what if we could pull the primary capacitor
out of the equations.
If we set the primary source and capacitor as a constant and assumed we had
a secondary which we could vary the resonant
frequency without really changing its load or coupling characteristics.  How
would number of turns on the primary affect
efficiency in that case???  I think the two important parameters here are
series impedance losses and the coupling between
a relatively small diameter primary and relatively large diameter primary.


Dan -

The limit to the number of primary turns is dependent on the primary
capacitor. This capacitor is an energy storing device and must be able to
store the proper amount of energy required for efficient operation of the
primary coil. This means the capacitor must meet several conditions, the
tuning requirement, the energy requirement, etc. You have to solve several
equations simultaneously. This is why engineering handbooks say "The design
of Tesla coils is empirical".

Start with the energy requirement -

        Cp = J/V^2    Assumes 50% efficiency

       J = Joules per bang
       V = Power supply secondary voltage

The tuning requirement is   LpCp = LsCs

Note that as you change the joules the Cp changes, the primary turns
changes, the efficiency changes, etc. There are other parameters and
equations involved. In general as the Cp is made smaller the primary turns
increase, and the efficiency decreases. A very small Cp gives you many
primary turns at very low efficiency. The trick is to find the optimum
operating parameters. Solving this problem with an NST only enhances the
challenge.

Your question in many forms has been asked many times in the past on the
List. The answers are always interesting.

John Couture

-----------------------------






-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Monday, January 27, 2003 1:29 AM
To: tesla-at-pupman-dot-com
Subject: Re: Practical limit to number of turns on primary ? ? ?


Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>"
<dhmccauley-at-spacecatlighting-dot-com>

Thanks for the replies, however they do not answer my question.  I am
already aware about the resonant relations between primary and secondary
etc...
My question, was what is the practical limit for size of the primary in
relation to the secondary coil.  This isn't a tuning question.  Its one of
efficiency and performance vs.
primary number of turns.  Of course this efficiency and performance vs.
primary number of turns would assume constant primary conductor size and
spacing.

Thanks

Dan