Hi gang,

Anyone know what differentiates a Tesla coil from any other old coil?
Is it simply that they all seem to be EHT types or is there some
particular quirk concerning the way they're wound? IOW, what sets 'em
apart?

thanks,

p.
--

"What is now proved was once only imagin'd." - William Blake, 1793.

"Paul Burridge" wrote in message
...
Hi gang,

Anyone know what differentiates a Tesla coil from any other old coil?
Is it simply that they all seem to be EHT types or is there some
particular quirk concerning the way they're wound? IOW, what sets 'em
apart?

They are operated in a resonant system, unlike an ordinary HV transformer.

Leon

On Sat, 27 Nov 2004 15:00:36 -0000, "Leon Heller"
wrote:

"Paul Burridge" wrote in message
.. .
Hi gang,

Anyone know what differentiates a Tesla coil from any other old coil?
Is it simply that they all seem to be EHT types or is there some
particular quirk concerning the way they're wound? IOW, what sets 'em
apart?

They are operated in a resonant system, unlike an ordinary HV transformer.

Thanks, Leon. Can you expand a bit? Are you suggesting that one or
both windings have some sort of parallel/series/real/parasitic
capacitance to bring the winding into resonance and if so, what's the
purpose behind it?
--

"What is now proved was once only imagin'd." - William Blake, 1793.

The secondary and primary are resonant with each other.

The self-capacitance of the secondary is all that is required.
(Compare with early Xtal sets that had an FGL, but
no tuning capacitor (or condenser for those days) in evidence.

"Paul Burridge" wrote in message
...
Anyone know what differentiates a Tesla coil from any other old coil?
Is it simply that they all seem to be EHT types or is there some
particular quirk concerning the way they're wound? IOW, what sets 'em
apart?

"Paul Burridge" wrote in message
...
On Sat, 27 Nov 2004 15:00:36 -0000, "Leon Heller"
wrote:

"Paul Burridge" wrote in message
. ..
Hi gang,

Anyone know what differentiates a Tesla coil from any other old coil?
Is it simply that they all seem to be EHT types or is there some
particular quirk concerning the way they're wound? IOW, what sets 'em
apart?

They are operated in a resonant system, unlike an ordinary HV transformer.

Thanks, Leon. Can you expand a bit? Are you suggesting that one or
both windings have some sort of parallel/series/real/parasitic
capacitance to bring the winding into resonance and if so, what's the
purpose behind it?

Try Googling, you'll find lots of stuff.

Leon

Anyone know what differentiates a Tesla coil from any other old coil?
Is it simply that they all seem to be EHT types or is there some
particular quirk concerning the way they're wound? IOW, what sets 'em
apart?
============================

Paul, I've never seen a Tesla coil or even recollect seeing a photo of one.
But I can imagine.

They are a means of generating very high voltages at relatively low radio
frequencies.

Low radio frequencies to minimise RF radiation losses.

The coil is quite an ordinary, single-layer, solenoid, close-wound or
relatively close wound in the form of a helix. Grounded at the lower end.
Open circuit at the top, high-voltage end.

It is coupled to the RF generator via a few turns link winding at the bottom
end.

Or the generator may be tapped into the bottom few turns.

The working frequency is that at which the coil is self-resonant with its
own distributed self-capacitance.

The generator, by virtue of the number of turns on the coil and the number
of the turns on the link coupling, is impedance-matched to the Q of the coil
such that all the generator power is dissipated in the coil's RF resistance.
This, of course, corresponds to maximum voltage at the top of the coil.

The situation is identical to a short HF helical antenna without a whip on
the top, operating say in the 160 or 80 metre band - but without the
radiation loss.

The radiation loss in the Tesla is low because its operating frequency is
low. Most of the power being dissipated in the wire resistance.

The theory is very simple. The coil inductance with its self-capacitance
must resonate at the working frequency. The coil Q must be very high and
the wire resistance must be low to generate a very high voltage.

Many turns of wire are needed to resonate at LF but the wire diameter must
be large enough to have a low resistance. Hence the larger the physical
size of the coil the higher is the attainable voltage.

The few number of turns on the link (or tap) coupling is calculable but is
better determined by experiment. One will always end up by pruning to match
to a particular generator impedance for maximum Tesla voltage.

The coil's inductance is easily calculated from well known formlae. The
coil's self-capacitance is more complicated. But what is really required is
the resonant frequency. Or it can be found by experiment. (Which is what
Tesla must have done.)

It so happens that my program SOLNOID3 will calculate the isolated
self-resonant frequency of a solenoidal coil from its dimensions. For Tesla
coils dimensions will be in metres and inductances of 10's of milli-henrys.

The practical design problem is insulation between adjacent coil turns. And
of course the driving power. Having never seen one my instinct guides me
towards a coil length to diameter ratio of 15-to-1.

Have you any intentions of making one?
----
Reg, G4FGQ

On Sat, 27 Nov 2004 13:52:07 +0000, Paul Burridge
wrote:

Hi gang,

Anyone know what differentiates a Tesla coil from any other old coil?
Is it simply that they all seem to be EHT types or is there some
particular quirk concerning the way they're wound? IOW, what sets 'em
apart?

thanks,

p.
Primary coil is a tank circuit (parallel LC usually) resonant with
the secondary coil. The secondary is usually placed inside the
primary coil.

While the primary is a parallel resonant circuit with a coil and
capacitor, the secondary is just a coil and series resonant, or a coil
with a large metallic body at the end to serve as a capacitor (spheres
and toroids are used to minimize corona loss)

A few turns of relatively large diameter wire or tubing in the primary
and a lot of turns in the secondary. 6:400 turns ratio is typical
enough for small systems, but that ratio isn't carved in stone.

The primary is wound as a helix or spiral, the secondary is wound on a
tube form, much longer than the diameter as a rule. Tuning the
primary to the secondary's resonant frequency is achieved via tapping
the primary coil with a movable tap.

Tesla or Oudin coils can easily produce hundreds of thousands of
volts. Lots of different forms and techniques are used to maximize
the output voltage - that's where it gets interesting.

The theory is simple - but building good coils takes experience.

They can be driven with high voltage transformers and spark gaps (the
most common technique) or vacuum tubes or solid state devices.

They are simple to build, good for high voltage experiments, producing
ozone, great visual effects, X rays, produce some RFI, etc..

There is a Tesla coil mailing list on the net that is very good. If
you want to build one (and I recommend it) they can be an invaluable
resource. http://www.pupman.com/ Lot of links to working tesla coils
and construction ideas.

Lindsay Publications www.lindsaybks.com is another source of books on
the topic (among others). Lindsay reprints books published at the
turn of the century (that would be the 1900's) on technology. It is
fascinating reading about tesla and induction coil construction - and
you can still build the stuff today with more modern materials. They
did have a paper catalog of their books in print - may still have it.

I built a few coils and a 1KW induction coil to drive them.

"Reg Edwards" wrote in message
...

Anyone know what differentiates a Tesla coil from any other old coil?
Is it simply that they all seem to be EHT types or is there some
particular quirk concerning the way they're wound? IOW, what sets 'em
apart?
============================

Paul, I've never seen a Tesla coil or even recollect seeing a photo of
one.
But I can imagine.

They are a means of generating very high voltages at relatively low radio
frequencies.

Low radio frequencies to minimise RF radiation losses.

The coil is quite an ordinary, single-layer, solenoid, close-wound or
relatively close wound in the form of a helix. Grounded at the lower end.
Open circuit at the top, high-voltage end.

It is coupled to the RF generator via a few turns link winding at the
bottom
end.

Or the generator may be tapped into the bottom few turns.

The working frequency is that at which the coil is self-resonant with its
own distributed self-capacitance.

The generator, by virtue of the number of turns on the coil and the number
of the turns on the link coupling, is impedance-matched to the Q of the
coil
such that all the generator power is dissipated in the coil's RF
resistance.
This, of course, corresponds to maximum voltage at the top of the coil.

The situation is identical to a short HF helical antenna without a whip on
the top, operating say in the 160 or 80 metre band - but without the
radiation loss.

The radiation loss in the Tesla is low because its operating frequency is
low. Most of the power being dissipated in the wire resistance.

The theory is very simple. The coil inductance with its self-capacitance
must resonate at the working frequency. The coil Q must be very high and
the wire resistance must be low to generate a very high voltage.

Many turns of wire are needed to resonate at LF but the wire diameter must
be large enough to have a low resistance. Hence the larger the physical
size of the coil the higher is the attainable voltage.

The few number of turns on the link (or tap) coupling is calculable but is
better determined by experiment. One will always end up by pruning to
match
to a particular generator impedance for maximum Tesla voltage.

The coil's inductance is easily calculated from well known formlae. The
coil's self-capacitance is more complicated. But what is really required
is
the resonant frequency. Or it can be found by experiment. (Which is what
Tesla must have done.)

It so happens that my program SOLNOID3 will calculate the isolated
self-resonant frequency of a solenoidal coil from its dimensions. For
Tesla
coils dimensions will be in metres and inductances of 10's of
milli-henrys.

The practical design problem is insulation between adjacent coil turns.
And
of course the driving power. Having never seen one my instinct guides me
towards a coil length to diameter ratio of 15-to-1.

Have you any intentions of making one?
----
Reg, G4FGQ



Of course, one must never forget Dr. Spottiswoode's 'Great induction coil';
first exhibited at a meeting of the Royal Institution held 13th of April
1877.
The wound secondary was 0.01inch diameter wire, 280 miles long. Primary was
1/2 mile of 0.1 inch wire, in // with a capacitor of 126 sheets of tin foil.
Powered fron 30 quarts of Grove's battery cells via a steam engine driven
Brass-Ebonite-Platinum interrupter, allowing 700 to 2500 impulses a second.
Generated arcs about 3.5 foot long!.
regards
john

On Sat, 27 Nov 2004 19:49:48 +0000 (UTC), "Reg Edwards"
wrote:

[snip science]

Have you any intentions of making one?
----
Reg, G4FGQ

Er, well, I ***was*** contemplating it, Reg...
--

"What is now proved was once only imagin'd." - William Blake, 1793.

Can we consider a standard car ignition coil a Tesla coil ? A cheap,
reliable and simple one.
There is primary with capacitor in distributor and secondary with self
resonance of course.
Good high voltage insulation is achieved with coil in oil bath .

Can we consider TV line transformer a Tesla coil or purely a transformer ?
It is produced to resonate in selected line frequency

I wonder how is normal neon light high tension generated.
Do they use some kind simple tesla coil system to ionize the rare cas inside
the glastubing or are they using choke like normal fluorescent tubes.
In any case neon lights seem to be safe for public with very simple
construction.
Safety protection with fluorescent lights is much and more complicated and
failsafe.

New questions made Risto; OH2BT