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Re: power vs. toroid size



Original poster: FutureT@xxxxxxx

In a message dated 3/30/05 10:30:01 PM Eastern Standard Time, tesla@xxxxxxxxxx writes:


Original poster: Skip Greiner <sgreiner@xxxxxxxxx>

I suspect that this subject may have been discussed before but I have been
unable to locate info in the archives.
Has work been done to determine the minimum power input to a TC to drive a
given sized toroid to breakout? I under stand that there are many factors
that might affect breakout including the roughness of the toroid surface,
humidity, etc. But I would think that, assuming some reasonable efficiency,
there should be some relational ship between power input and the ability to
get breakout from the toroid. I would think that when designing a new TC,
one would have to take into consideration the possible sizes for the toroid
when setting the parameters for the secondary. Any comments would be
appreciated.
Skip


Skip,

Yes, there has been postings about this in the past.  Paul N. did
some tabulations and calculations of actual coils which is probably
at his website.

I also wrote some general comments about my findings in that regard.
There's definitely a relationship as you suggested.  Consider my
TT-42 coil.  This coil uses a robust 12/30 NST and gives 42" sparks.
I normally use a 4" x 13" smooth toroid, but in a test I installed
a 6" x 24" smooth toroid.  This toroid was just on the edge of
breakout at an input wattage (wallplug) of about 800 watts or so.
Using the 6" x 24" toroid, the spark length increased to 44" or
46".  I can't seem to remember exactly, but the sparks were
longer.  I think they were 44".

I use a rule of thumb for toroid size vs. power input.  It follows
a similar square law such as I use for input power vs. spark length.

Generally folks want to obtain more than a single streamer for
a better looking discharge, so a toroid size is chosen that is
somewhat smaller than the maximum size that can break out.
For example I use the 4" x 13" toroid on the TT-42 coil, but
the spark can actually break out of the 6" x 24" toroid.
Something like  < toroid total dia in inches = 0.5sqrt input power >  can
work for a useful toroid size.

One of my articles appeared in TCBA news some time ago that gave my
complete rule of thumb equations for designing such coils.
I probably posted it on this list also.

Consider Richard Hull's nemesis coil.  THis used 11 to 13kW
and used a 60" toroid.  My formula gives 55" dia, so it's pretty
close especially since he used a corrregated toroid.  My TT-42
uses 800 watts, so the formula gives 14".  I use a 13" smooth
toroid so again the formula is close.

It seems that at higher breakrates, a smaller toroid will suffice
due to the smaller bang-size.  Not much research has been done
in this area however.

Cheers,
John