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Measuring Secondary Coils
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From: John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
Sent: Friday, August 21, 1998 8:55 AM
To: Tesla List
Subject: Re: Measuring Secondary Coils
Chris, Reinhard, All -
I agree with Reinhard that the calcs and testing of Tesla coils are not
to be taken lightly. For over 10 years I have been hearing coilers say that
the equations and calculations do not work because they do not agree with
tests. In all of the cases where I have had enough info I found that these
coilers did not understand how to do the calcs or tests properly. When the
calcs and tests were done properly the calcs and tests would agree.
The problem is that many of the usual tests shown in the literature are
not well suited for Tesla coil work and it is easy to misunderstand the
results. I wrote three books which gave some of the necessary information
but there is a lot more that can be written about how to do the calcs and
tests adequately for Tesla coil systems. Of course, now the Internet is
providing more info but this information is scattered and not coordinated.
What is needed is for someone to write a book on testing Tesla coils,
including waveforms. JHC Engineering has no plans for such a book.
Any coiler who has written a computer program for Tesla coils knows that
the calculated outputs will only agree with tests when the user provides
accurate values for the inputs and the tests are done right. The biggest
pitfall is understanding how to handle the secondary terminal capacitance
and the coil self capacitance. The next in importance is in finding the
correct test frequency values which are sometimes squared in the calcs.
There are several tests that can be used to measure the inductance of a
coil and the capacitance of a capacitor but only certain tests are best for
Tesla coils. There are many other pitfalls of which the coiler must be
aware.
John Couture
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At 11:16 PM 8/20/98 -0500, you wrote:
>
>----------
>From: RWB355-at-aol-dot-com [SMTP:RWB355-at-aol-dot-com]
>Sent: Thursday, August 20, 1998 5:18 PM
>To: fwd
>Subject: Re:Measuring Secondary Coils
>
>---------
>From: chris.swinson [SMTP:chris.swinson-at-zetnet.co.uk]
>Sent: Wednesday, August 19, 1998 7:44 AM
>To: Tesla List
>Subject: Secondary Frequency
><SNIP>
>
>Hi Chris, all !!
>
>Chris
>
>I hope you are not thinking of just "plugging" a capacitor and/or inductance
> meter across your secondary coil and then just reading what the meter tells
> you. That doesnīt work !! The measuring frequency of these meters is way too
> low to give an accurate reading of the inductance (capacitance) the coil has
> at "our" operating frequencies. Typical DMMīs run at about 200Hz better ones
> at 400Hz or 1000Hz. I donīt know, however, if there are RF "adjusted" meters
> that would be able to really measure the values correctly.
>
>Otherwise, the only way I think you could do it properly, would be to connect
> a frequency gen and an O-scope to the coil via a Wheatstone bridge. That way
> you could find the frequency at which the coil resonates, but you would
still
> have to calc the (unknown) inductance/ capacitance part of the bridge (read:
> your coil). So you would be back to square one.
> I suppose you stepped into the same bear trap I did and used wire length
as a
> grounds for your calculations. And as many coilers have proven (and if you
> think about it is pretty logical, too) the 1/4 wave theory will sink you
like
> a leaky submarine.
>
>Regards and safe coiling,
>Reinhard