RE: FW: Re: Tesla Coil Efficiency Test

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

Original poster: "Dave Larkin by way of Terry Fritz <twftesla-at-qwest-dot-net>" <teslaman15-at-hotmail-dot-com>

>Tesla coil efficiency is a tricky business. I found that out several years
>ago when I was developing the JHCTES computer programs. At that time 
>coilers
>were mostly interested in how to make the calculations work. That is the
>tuning equation  LpCp = LsCs  could not be made to work (to agree with
>tests) so building a TC was a matter of trial and error construction.
>
>Of course today we know why this tuning equation did not work and now
>consider it elementary. However, for someone trying to make a computer

Why exactly?  LpCp = LsCs seems to hold pretty well for all my coils.  Maybe 
in the old days people's calculations of the circuit values were a bit 
wonky?

>program that resonably represents the TC system the problem with this 
>tuning
>equation had to be solved. This tuning equation was fundamental to any TC
>program and something like TC efficiency was considered to be of secondary
>importance.
>
>The JHCTES Ver 3.3 TC program represents the latest product in my struggle
>to come up with a program that could easily be used by any coiler with a
>high school education. This program not only solves the tuning equation
>correctly but it also produces outputs that are always in tune with the
>inputs. This was an improvement compared to other programs available at the
>time. These programs could result in untuned coil designs.
>
>  Over the years this program has been used by many coilers to design their
>coils. It was natural that many questions regarding TC design would by
>raised. One of the many questions that came up had to do with TC 
>efficiency.
>The JHCTES program does not show a parameter for efficiency. However,
>coilers could estimate TC efficiency  by using the "watts/Ft of spark" in

Ahhhh......  You mean larger coils are less 'efficient' in terms of watts/ft 
of spark length, whereas I meant they are more efficient in the conventional 
sense, ie. power in vs. power out.  IMHO watts/ft has nothing to do with 
efficiency, it is independent of a coil's design and is merely a scale 
effect as one trys to extend the spark channel.

>the JHCTES Ver 3.3 program output. It came as a surprise to me to find out
>that the program showed the TC efficiency not only as increasing with
>increasing TC size but also decreasing with increasing TC size.
>
>With this increasing/decreasing situation it was obvious that coilers would
>have a hard time deciding how to interpret what the program was showing and
>this appears to be the position we are in today. For example, the JHCTES 
>Ver
>3.3 program shows that if you increase only the number of turns on the
>secondary the "watts/Ft of spark" will decrease indicating that the TC
>efficiency increases as the TC is made larger. This can give a coiler the
>false impression that larger TC's are more efficient. You can find other
>examples if you experiment with the program.
>
>It should be noted, however, that when the TC system is truly increased in
>size by increasing the input wattage the "watts\Ft of spark" will always
>increase indicating the TC efficiency decreases when the TC is made larger.
>In other words with the TC system if you take only a PART of the system you
>can sometimes show that the TC efficiency increases with an increase of one
>of the parameters. This occurs because we are then talking about a 
>different
>coil. However, the total TC system efficiency will always decrease when the
>TC system is increased in size by increasing the watts input.
>
>Most coilers today prefer to design their coils using a TC computer program
>so an understanding of how the program works is important. You can find 
>many
>other parameters with the program than the ones actually shown. The TC
>efficiency is one of these parameters. There is much more to TC efficiency
>and I will be posting more information that shows how the TC efficiency can
>be determined when the correct tests are made.
>
>You say the TC efficiency increases when the TC is made larger. All the 
>data
>I have seen indicates that TC efficiency decreases as the TC is made 
>larger.

Well..... analysis by Terry Fritz and Greg Leyh would suggest that small 
coils (~0.5kVA) normally burn ~50% of their input power in the spark gap, 
whereas big coils (~45kVA) burn less than 20% of their power in the spark 
gap. Admittedly the 45kVA datapoint was an estimated value for only one 
large coil system, but from my own experience in the 10kW region I have a 
lot of trouble believing that my spark gap is burning more than 2kW, and 
certainly nowhere near 5kW.

>I would be interested in the data and calculations you have available that
>shows the TC efficiency increases when the TC is made larger.
>
>The black box efficiency is easily measured by measuring the watts input 
>and
>the watts output.
>Energy = watts x seconds
>The TC efficiency is   Eff = watts out/watts in
>A problem arises when measuring the watts out when using sparks as outputs.
>However, there is no problem if an incandescent lamp is used as an output.

How exactly is the incandescent lamp connected to simulate the streamer 
load?  I would have thought a suitably proportioned resistor string in the 
region of 100-200kOhms would provide a more accurate (although still pretty 
poor) dummy load.

-Dave-