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 -

I agree the input power and spark length don't scale in the same proportions
but that does not mean that watts/ft of spark can't be used as an indicator
of TC efficiency. You only need to know what these proportions are and we
have this information from actual tests.

watts in/ft spark = watt secs/spark energy = joules/joules

At present tests have shown that for a TC output spark range of 1 to 40 ft
the watts/ft of spark is about 200 to 1200. This represents TC inputs of 200
to 48000 watts input. This gives us the proportions we need. Assuming the TC
efficiency of the 1 ft spark coil is 50% the efficiency for coils up to 40
ft can be found as follows
        48 KW eff = .50 x 200/1200 = .083 or 8.3%

Tests may indicate this equation is non linear. In this event we  may have
to adjust it to agree with tests when they are made. The lamp test appears
to be a good test for verification. This would be only for classical coils
so the design/geometry would be well defined. It is obvious from the above
that when the TC is increased in size the efficiency decreases.

Keep in mind that the lamp test is not dependent on the charateristics of
the lamp. Only a single light level is used for each test and the
calibration for that level is made after and not before each test. Of
course, there is still the question as to how accurately the lamp test
represents the TC spark operation. This will have to be determined by tests.
Refer to my posts to Dave and Bart.

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. This method may indicate
that the TC efficiency can increase or decrease with an increase in the size
of the TC as I mentioned in an earlier post. The TC efficiency found in this
manner would always be greater than the TC efficiency found by the lamp
method because of the omitted losses. One of these losses is related to when
the energy in the toroid (.5CV^2) is converted to the energy in the spark.
Would this spark discharge loss be 50% of the energy in the toroid?

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

John Couture

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


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Saturday, June 29, 2002 9:15 PM
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>

Dave Larkin wrote:

> IMHO watts/ft has nothing to do with efficiency, it is
> independent of a coil's design and is merely a scale effect

Well said.  Input power and spark length don't scale in the
same proportions, so it would only do as a comparitive performance
measure for coils of similar design/geometry, and is useless as
an efficiency metric.  Keep it for the scoreboard at a Teslathon.

> How exactly is the incandescent lamp connected to simulate
> the streamer load?

Indeed.  Doesn't the bulb test just measure the efficiency of
power coupling to that particular bulb?  Change the bulb, or
alter the way it's coupled and you'll get a completely different
figure for efficiency.  Seems to me that the bulb testing is
limited to optimising the efficiency of the supply-side of the
primary cap, where you're just interested in maximising the
bang energy and gap efficiency.  But then only as a relative
indicator for a particular coil.

I don't see any defects with the method proposed by Malcolm.
You can arrive at an unambiguous figure for efficiency: the
percentage of bang energy going into the streamers.  What more
could you want?  And you don't have to decide whether 3 streamers
at 4 foot length is equivalent to 2 at 6 foot length, etc.
Instead you get an actual percentage efficiency which you can
multiply by the input power to determine the watts delivered to
streamers.

But, what John is striving for is a test that can be carried
out simply, without needing a fancy scope.  Perhaps we can think
of a way in which the decay rate of the secondary base current
beat envelope can be metered easily?  Something like a bridge
arrangement in which an adjustable RC decay is compared with
a peak-detected base current sample?

And to satisfy Bart, we *are* still using the spark output as a
performance metric, just that by looking at the beat decay we
are getting directly at the energy involved, instead of by the
rather more indirectly related 'spark length'.

And just a slight variation on the theme gives you the percentage
bang energy dissipated in the gap.  The words gifthorse and mouth
come to mind, as well as mountain and molehill.
--
Paul Nicholson
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