Re: FW: Re: Tesla Coil Efficiency Test

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

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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