Re: High amperage in tank circuit

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

Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>

Hi John,

At 01:32 PM 3/30/2003 -0600, you wrote:
>Hello,
>
>I have a few questions that I was hoping someone could answer in beginners 
>terminology, or could possibly give me a link with basic explanations:
>
>First, I hear everyone talking about the importance of large wire in tank 
>connections, and the explanations that I have read all point to the fact 
>that the currents can reach potentials of hundreds of amps.  The thing 
>that I am not understanding, is how can we reach this kind of potential 
>from supplies which are putting out much less than an amp?  I can see the 
>potential for high amperages in capacitor discharge experiments, where the 
>charge time for a cap bank can exceed several minutes or more with a small 
>power supply (like a neon), but we are talking about discharging the 
>capacitor in a TC a minimum of 120 times/sec.  How is it possible to reach 
>these high currents in short periods of time?

Tank circuits run at a few hundred to a few thousand amps.  We could guess 
about 700 amps is typical.  We can charge our relatively small caps to 
about 5 Joules in 1/120 of a second with the power from an NST.  If we have 
a cap charged to say 20,000 volts and we short it, there are two things 
that limit the current, resistance of the tank circuit and the inductance 
of the primary coil.  The spark gap is the largest resistance by far at 
about 3 ohms.  If we just short the cap with that resistance we get 20000 / 
3 = 6666 amps!  That is why you don't want to directly short Tesla tank 
caps.  That high current will damage them.

The real current limiter is the inductance of the primary coil (the 
secondary has some effect too, but will ignore it).  The primary coil has 
an inductive "reactance" that acts much like a resistance.  This reactance 
is say 80 ohms and really defines the primary tank current.  20000 / 80 = 
250 amps.

Inductive Reactance = Xl = SQRT( Lpri / Cpri )

So If we have a 25nF cap at 20000 volts and a 100uH primary coil, the peak 
current is:

Xl = SQRT( Lpri / Cpri ) = SQRT ( 100uH / 25nF ) = 63.25 ohms

I = V / R = 20000 / 63.25 = 316 amps peak.


>
>Second, it is well known that in a synch RSG, everyone strives for 
>electrode alignment at the peak of the 120 or 240 input sine wave.  I was 
>under the understanding that during transformer action, a voltage is 
>induced when the magnetic field collapses, not as it rises.  In light of 
>this, it would seem to me that secondary voltage would rise to a peak as 
>the primary field collapses, and to extrapolate this further, the 
>secondary voltage rise would top out as the primary approaches zero on the 
>sine wave.  Therefore, the RSG electrodes should be aligned somewhere 
>between 45 and 90 degrees after the input peak, which is when the 
>secondary would be topping out voltage wise and the capacitor would be 
>fully charged.  Obviously this isn't correct, but I need some help to 
>understand what is really happening.

We do want to fire on the peak voltage.  However, the inductances, stored 
energies and all skew the timing.  May big coil fires a few milliseconds 
off from the AC line.  So we do use the AC line as a reference, but one 
usually has to adjust the timing differently than just the AC line 
timing.  One can calculate this timing, but it is afar easier just to 
fiddle with it for the best spark output.

LTR Tesla coils actually fire significantly after the voltage peak since 
they are trying to such extra power out of the energy stored in the NSTs 
secondary inductance.

http://hot-streamer-dot-com/TeslaCoils/MyPapers/modact/modact.html


>
>Finally, could someone point me to a link which explains the theory behind 
>a voltage multiplier?  I have been checking like crazy, and can't find an 
>explanation that I can understand.  It's hard for me to grasp the concept 
>of diodes and capacitors multiplying voltage.

I could not find any good links on this.  But here is a cool one :o))

http://members.tm-dot-net/lapointe/Cockcroft_Walton.htm

These are usually called "Cockcroft Walton Voltage Multipliers" so that is 
the term you should search on.

BTW - This person has a very interesting page!!!

http://members.tm-dot-net/lapointe/Main.html

Cheers,

         Terry



>
>Thanks, and the simpler the explanation or the link, the better.
>
>John Richardson