RE: [jlnlabs] TESLA COIL REVISED

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

Original poster: "John H. Couture" <couturejh-at-mgte-dot-com> 


Jaro -

Your type of question is good for Tesla coilers. These questions make the
typical coilers review their understanding of how Tesla coils works. What
you say is true that Tesla used coils with much fewer turns than today's
TC's. Tesla was an engineer and obviously knew what he was doing. How do you
explain this less turns from a theoretical standpoint?

I believe the difference in the number of turns is partially explained by
the fact that TC's relie on the flux linkages between the primary and
secondary coils.  Flux linkages are determined by ampere turns. In other
words you can either have large amperes or large number of turns and get the
same results. The problem, however, is that coilers normally ignore flux
linkages in the design of their Tesla coils. They concentrate on other TC
parameters that also affect the spark length like input power, losses,
secondary inductance, etc.

A good example of coilers ignoring flux linkages is in the design of the
primary coil. They will use small primary wire sizes and ignore the high
primary currents that the primary must carry. Coilers hardly ever use a
primary wire size that corrolates to the current carrying capacity of the
wire size to the primary current during TC operation. In other words if the
tuning of his TC requires only a few primary turns he will need a larger
wire compared to a primary with many turns. Coilers seldom if ever balance
the ampere turn parameter. Several years ago I was interested in this design
problem and developed two graphs of recommended wire sizes, one for the
primary and one for the secondary. The graphs are shown in my TC Design
Manual. As for the secondary turns, an interesting fact about reducing the
secondary turns is that the K factor is increased but that is another story.

Your one turn primary and 50 turn secondary would be OK except it would be
ignoring the other parameters that affect the spark length. Even if you had
the right primary and secondary wire sizes you would end up with a shorter
output spark length. Tesla's coils took care of the other parameters by
making the TC larger.

John Couture.

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


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Tuesday, December 30, 2003 1:01 PM
To: tesla-at-pupman-dot-com
Subject: Fwd: [jlnlabs] TESLA COIL REVISED


Original poster: Tom Stathes <newphreak_16-at-yahoo-dot-com>


Note: forwarded message attached.


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Date: Sat, 27 Dec 2003 06:54:13 -0800
Subject: [jlnlabs] TESLA COIL REVISED
Reply-To: jlnlabs-at-yahoogroups-dot-com
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I have a problem with today's Tesla coils. The way they're built these
days, is with the secondary made with SEVERAL HUNDRED turns of thin
wire, which is WRONG. When Nikola Tesla made his coils, they only had
50 to 100 turns of a THICK wire as the secondary.

The problem with hundreds of turns of a thin wire is that they have
many times bigger resistance than Tesla's original coils. This big
resistance increases losses, and so minimizes voltage increase due to
resonance. Thick secondary wire will have small losses which allows the
resonance to build higher voltages.

Here's how Tesla's Colorado Springs coil was built. Primary were 2
turns of a thick cable, and secondary 100 turns of No. 8 wire with a
diameter of 51 feet. That's 1:50 ratio between primary and secondary.
Input was 50 kV into a .004 mF capacitor which was connected to the
primary coil through a spark gap. It could resonate at frequencies from
45 to 150kHz.

Tesla's power-transmission coil patent shows almost the same coil,
except that the diameter was 8 feet, and secondary was wound as a flat
coil (also no. 8 wire), and resonance was around 250kHz, producing 2 to
4 million volts.

So if Tesla's coil could be reduced from 51' diam. to 8' diam., while
keeping the 1:50 primary/secondary ratio, then it should be no problem
to reduce that coil further to about 1' diameter, using only 50 turns
of a thick wire as a secondary.

The only problem would be the 50kV input that Tesla used, but even
using only 5kV from a neon transformer should produce 200 to 400kV
using the 1:50 ratio, since 50kV input produced 2-4 million volts.

Also, using a 1' diam. secondary will reduce its inductance, which
will increase resonant frequency to several MHz. And using a very thick
wire, copper pipe or Litz wire would be needed to reduce high frequency
losses.

So, using a 1-turn primary and 50-turn secondary on a 1-foot diameter
air-core, should make a TRUE Tesla coil which will have lower losses
and more powerful resonance than today's "Tesla coils". Plus that makes
it much easier to make than winding hundreds of turns.

Jaro