RE: FW: Re: Tesla Coil Efficiency Test

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

Original poster: "John H. Couture by way of Terry Fritz <twftesla-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>


Paul -

How the loss of energy is determined when the energy is transfered between
the secondary coil and the lamp is a problem that will have to be solved for
this test. One possible test is to use the coupling test I show in the TC
Construction Guide. The coupling factor is found by
        K = sqrt(1-(Fo/Fs))

With the pickup coil wire wound tightly around the bottom of the secondary
coil the coupling would be high, something like 0.6 or higher. The wattage
output found by the lamp test could then be divided by this coupling giving
a new larger wattage output. This could give the true overall TC efficiency.
However, this would be a secondary coil to load loss only for a particular
type of lamp load.

The problem that you mentioned regarding how the lamp load can be made to
represent the streamer load may be even more difficult to resolve. How do
you make a continuous constant electrical load represent an intermittent
spark load? For example at 120 BPS does dividing the total watts of the lamp
load by 120 to represent a spark output make sense?

There is still another problem that will have to be solved. How to find the
optimum test lamp voltage and wattage as the Tesla coil becomes larger. I
tried to estimate this voltage and wattage in my original meager research
but things got complicated and I ran out of time. In general I found the
larger the TC the higher the lamp voltage and wattage that was needed.

I agree it appears that we can define a measurable "efficiency" of a TC
provided we make clear what type of output we are using, such as lamp
output, spark discharge, ringdown, etc.

John Couture

-------------------------------


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Friday, July 05, 2002 11:48 AM
To: tesla-at-pupman-dot-com
Subject: Re: FW: Re: Tesla Coil Efficiency Test


Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<paul-at-abelian.demon.co.uk>

John Couture wrote:

> Keep in mind that the lamp test is not dependent on the
> charateristics of the lamp.

It's appreciated that the single level comparison avoids
calibration or linearity issues.

However, the problem with the lamp test is that the number it
produces refers to the efficiency of energy transfer to that
particular lamp with that particular degree of coupling to the
secondary coil.

If you run the test with the lamp fairly loosely coupled to
the coil, you'll get a smaller value for the apparent efficiency
than you would if the lamp was coupled more tightly.

For the lamp test to be a viable method for assessing the
efficiency of the coil when operating into a streamer loading,
then somehow you will have to adjust the coupling of the lamp
so that it dissipates the same fraction of stored energy per
cycle (on average) as does the streamer load during operation.

> Malcolm's transfer method for finding the TC efficiency does
> have merit.  However, it must be understood that this represents
> only the efficiency of a part of the TC system and some losses
> sre left out.

Yes, I agree. We only get the efficiency of the RF parts of the
system by using methods based on ringdown.  Losses in supply
transformers, ballasts, PFC, etc are invisible.  The lamp test
does give an overall efficiency, rather than just an RF efficiency.

I don't see any fundamental problem with defining a measurable
'efficiency' of a TC, providing you are clear on what you consider
the 'output' to be.  For example, if you choose the streamers to
be the output (as opposed to spark discharges to ground, or energy
coupled to a receiver coil), then by measuring the ringdown times
at just above and just below breakout, and treating these as loaded
and unloaded Q factors respectively, the RF efficiency can be
calculated in the normal way just as you would for any other tank
circuit.  As another example, if you were wanting to transfer
power to a wireless load, for example an inductively coupled lamp,
then you would measure the ringdown times with and without the
lamp circuit closed to obtain the RF efficiency of coupling to the
lamp.   Similarly for other loads which give a meaningful
average decay rate to the stored energy.  Spark discharges to
earth don't meet this qualification and a modification to the
ringdown test is required for this, but the RF efficiency is still
obtainable.

> The decay rate of the secondary base current sounds interesting.
> How would you do the metering to find the energies?

The RF efficiency obtained by ringdown tests must be qualified by
an input power measurement, the BPS, and either a firing voltage or
a peak primary current measurement in order to obtain the energies
and an overall efficiency figure

All in all, the lamp test would be a much simpler and more
accessible method, if some way could be found to ensure that the
lamp loaded the resonator down to the same Q (and same Fres for
that matter) as the operational streamer load (or some other
definition of output) does.
--
Paul Nicholson
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