Re: [TCML] Low power Tesla Coils producing DC spark phenomena

[<pterren@xxxxxxxxxxxx>]

I could be completely wrong here but a few thoughts on DC in Tesla coils.

Firstly, an induction coil is fed by a sharp spike in one direction as 
contacts meet and DC is fed to the coil primary. The back EMF when the 
contacts open is dampened by a "condensor" across the points.  The induction 
coil should give an asymmetrical output and be more DC in nature.
One commercial induction coil advertising 100kv had a positive and negative 
polarity switch, presumably on this principle.  Note there is no resonance 
to give an AC ringing to counteract the DC.

Secondly I believe that small TC's tend to be a bit polarised and I base 
this on the performance with an ion spinner. These work great on my small 
briefcase TC which is not tuned.  They do not work at all on my medium TC 
with 4 foot sparks.  Even with a 14 foot spinner just 60 kV DC will send it 
happily spinning but the TC will not budge it in the slightest. The 
difference perhaps is that a properly resonant system will be AC rather than 
a pulse of DC.

Jes sayin'.
Peter
http://tesladownunder.com/Lifters.htm#IonicSpinners
(new bigger site has taken 2 years and should be ready in 6 months)



-----Original Message----- 
From: Jeff Behary
Sent: Monday, September 02, 2013 11:34 AM
To: tesla@xxxxxxxxxx
Subject: [TCML] Low power Tesla Coils producing DC spark phenomena

Most know the story of how I came across the glass plate negatives of TB 
Kinraide, and the mysteries discussed over the years concerning why his 
spark photos made
with high frequency coils showed distinct positive and negative polarities. 
In replicating his work, the output my low power coils was exactly the same 
as his,
faint brush or corona discharges of unusually distinct shapes, 1/2" thick 
forked positive discharges and unusual feather shaped plume-like negative 
discharge - often
appearing with little logic as to why, united back-to-back, and even 
changing polarity with even minute (1/10,000th of an inch) adjustments of 
the spark gap.

The following video shows a 3.5kV 8mA NST connected to a .01 mfd condenser. 
A small micrometer spark gap was inserted in series with an 
Oscilloscope/Ondoscope tube used to show polarity for induction coils. 
These tubes were little more than geissler tubes with two very closely 
spaced wires that almost meet in the middle.  When operated from oscillatory 
currents both wires glow evenly (as in the start of the video).  When 
operated with pure DC the negative wire lights brightly. When operated with 
"dirty" DC (as in an induction coil with a lot of "inverse currents") the 
negative lights as well as part of the positive wire.  In the early X-Ray 
days spark gaps were often inserted in series with the X-Rays tubes to 
correct the inverse currents, and when an oscilloscope is used to show 
polarity the condition will change from an impure DC to a pure DC once the 
gap was opened beyond the voltage of the induced currents in the "make" of 
the circuit.  This filtered them out to a certain
extent and left only the desirable "break" currents...

https://www.youtube.com/watch?v=j0A0-izBdnI

In the video you can see that the polarity is rather distinct positive or 
negative at some moments and partially DC with oscillations present at other 
times, and still purely oscillatory at other times.  The only thing changing 
is the length of the spark gap.

So at low powers, there is a sort of rectification taking place somehow with 
the inductance of the transformer and capacity of the cap in combination 
with a spark gap.  By replacing the tube with a Pancake Coil of relatively 
few turns (2 1/2 turns on the primary, 200 on the secondary) these unusual 
discharges take place, forked branches 1/2" thick in all directions and over 
a foot long under certain conditions of the gap when favorable.  At other 
instances shorter 2-3" negative plumes can be seen interspaced, often with a 
positive oscillation occurring from the surrounding air.  And still at other 
instances it operates like a normal oscillatory Tesla Coil.
It explains the unusual nature of Kinraide's spark photos.   The sound of 
the spark gap is unusual as well, some of these effects can be heard or 
distinguished by the sound of the gap without even looking at the coil/tube. 
It's strange, but consistent.

I've shared this in person with some of the top lightning experts in the 
country.  The distinct polarity of little more than  a normal TC circuit 
operated with low powers was not expected, but definitely is the case.  A 
proper explanation might be given by others, Bert I'm sure will comment 
better.   Funny to think a low powered Tesla coil actually behaves 
differently (and drastically so) from a normal powered coil.

Jeff

_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla