Voltage/Length (fwd)

From:  John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
Sent:  Wednesday, January 21, 1998 6:13 PM
To:  Tesla List
Subject:  Re: Voltage/Length (fwd)

  Greg -

  The equation you used to find the TC secondary circuit voltage
            Joules = .5 x C x V^2
can be used to find the joules, capacitance, or voltage in the TC primary
circuit. These joules or energy will appear in the secondary circuit with a
certain efficiency. However, this joule equation cannot be used to find the
TC secondary voltage. In the pri circuit the voltage is RMS, 60 Hz, but in
the secondary the voltage is of an instantaneous dampened wave type. The
dampened wave can be seen on an oscilloscope and the peak amplitude
estimated. However, this is not of much use because this is not the voltage
to which the secondary terminal is charged.

  The secondary terminal is charged to various voltages giving varying spark
lengths and sometimes a rare long spark that coilers use to rate their
coils. The important fact is to understand that the sparks require large
voltages, large instantaneous power, but low energies. This type of
operation is possible because the Tesla coil can magnify power but not enrgy. 

The energy and power at the wall plug and also in the TC primary circuit can
be low. However, in the secondary circuit the energy is low but the
instantaneous power can be very large producing very high sec voltages and
long sparks. A typical TC energy/power calculation is shown in the Tesla
Coil Construction Guide page 5-5. This coil was built and tested by three
scientist in 1930. The input power was 3 KW and the output  instantaneous
power was 1700 KW, a power gain of 567 at 25 % overall efficiency.

  To calculate the sec voltages requires empirical data. Programs like
PSPICE do not have this TC data so cannot estimate the sec voltages with
resonable accuracy. To circumvent this barrier the JHCTES program uses a
different approach. The program uses an equation that was derived from real
coil data to give TC sec voltages and spark lengths that appear to agree
with the real world. 

  At present the Tesla coil world is waiting for something better to come along.

  John Couture


At 08:17 AM 1/20/98 +0000, you wrote:
>From: 	Greg Leyh[SMTP:lod-at-pacbell-dot-net]
>Sent: 	Monday, January 19, 1998 1:21 PM
>To: 	Tesla List
>Subject: 	Re: Voltage/Length (fwd)

------------------------------------------  snip

>The secondary is 20000 Ohms at resonance (2pi x 62kHz x 52mH), 
>and 20000 x 25A = 500kV.  PSPICE gives values anywhere from 
>300kV to 750kV, depending on what secondary model I use!  
>I feel that I still don't have a good model.
>Multi-Megavolt estimates of output voltages are wildly optimistic 
>for most coils.  A simple energy balance calculation can show that.
>Consider a coil with 100pF of sec capacitance, and 3MV of claimed
>output voltage.  The claimed stored energy in the sec would then be 
>450 Joules, and with an coil efficiency of say 60%, gives a primary 
>cap energy of 750 Joules!! (most coils run at less than 80 Joules)
>Now at 240 breaks/sec that's 180,000 watts of req'd wallplug power!! 
>And the stored energy and power requirements would increase from here
>with the square of the claimed output voltage.  
>The Multi-Megavolt ratings do sound better in advertisements however.