Tesla Coils & MS EXCEL

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

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


For coilers who dislike to do the math required of Tesla coils the MS Excel
program is one of the best design instruments to use. It is also a great way
to use as a circuit simulation program. Just about any type TC program can
be simulated with Excel. The main problem is to be able to set up the
equations in the spreadsheet before you can proceed. You can then solve
almost any TC algebraic, calculus, or differential equation problems you are
interested in researching with no math. Note that simulations can also be
duplicated with graphs. The following is for the TC input parameters. The
tuning and output parameters are another story.

Finding the input watts of an operating TC using the "three voltages and
series resistor" method  is one of the many TC simulations you can do
without having to do the math. I was interested in doing this by using 15
variables including the three voltages and the series resistor. I wanted to
find the input watts and the power factor and produce graphs that showed how
these parameters varied with different TC parameters like a simulator would
show. It is obvious that just knowing the input wattage is not enough
because any wattage with low power factor is very inefficient.

Like simulations there are hundreds of possibilities and dozens of graphs
are required. However, once Excel is setup no calcs are required and only
four inputs are needed and you can make as many graphs as you need. The
other 11 or more parameters are calculated by the computer. I found the
curves for the input wattage and power factor varied greatly and not as you
would suspect.

I haven't completed the work and wondered if other coilers are making
similar Excel graphs. I found that you cannot just arbitrarily enter the
"three voltages" and do the calcs. If you do this you will soon find out
that it doesn't work. You can easily end up with efficiencies over 100%.
These three voltages are very special in combination (that is why they are
used) and are like the parameters for the TC tuning problem. If they are not
properly coordinated they will be "out of tune" and the answers will be
GIGO.

The way to avoid the three voltage GIGO problem is to use only one of these
variables as the input and solve for the other two. To do this you need to
solve for other variables. That is where the graphs come into use. You
develop graphs that represent many TC parameters using only four inputs. The
four inputs are the voltage across the load (V1), the series resistor ohms
(RS), the load inductance (XL), and the load resistance (RL). With Excel
properly setup you can then find all the other TC input parameters. It is
obvious that the power factors must be high to get high efficiency so you
need to find the PF.

For example take four inputs V1 = 120 volts, RS = 5 ohms, XL = 40 ohms, RL =
40 ohms. This is all the info you need to find any of the 11 plus input
parameters in your TC. The computer will give you the input impedance,
circuit current, wattage, power factor, etc. With the above inputs the input
impedance is 60.21 ohms, the RS special voltage is 9.97 volts, the voltage
across the load is 112.75 volts, the load watts is 158.9 watts, the load
power factor is 40.51%, the overall efficiency is 66.54%, etc. Look MA, no
MATH.

The computer with Excel and these four inputs will give you the other two
special voltages that tell you the wattage, power factor etc. This is the
only way to get these voltages correct except by building and testing the
coil. The voltages will also be always  "in tune". The only other way would
be to build the coils and actually test for these three voltages. You can
change the four inputs and obtain any TC input conditions of you coils
without any math and in many cases better than with a circuit simulator.

This design method will tell you how to get the most wattage and energy into
your TC for maximum efficiency. To my knowledge these design graphs have
never been developed before now.

John Couture

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