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RE: NST power rating con



Original poster: "John H. Couture" <couturejh-at-mgte-dot-com> 


Tom -

There is only one test to find the maximum watts output of your NST. You
need a HV voltmeter, ma meter, and a bunch of "power" resistors. Then make a
graph of output watts vs the resistive load. I did this with a 7500 V, 30
ma, 225 watt NST. The maximum secondary watts output was 59.3 watts, 3900
volts, 15.2 ma. The input was 120 volts, 1.45 amps, 174 VA, 60 watts, 34.5%
PF. The NST overall efficiency was 98.8% at maximum output!! The efficiency
drops to 22% with an 8.0 Kohms load.

    Overall efficiency % = 59.3/60 = 98.8%

Many other tests (1980's) gave surprising results. With certain combination
loads of resistors and capacitors it was possible to make graphs with VA
output greater than VA input! It is obvious the NST with a TC load can be an
interesting challenge when it comes to creating an equation for output spark
length. John Freau's equation is about as good as it gets.

This all means that for TC's the NST nameplate rating must be used with the
utmost caution.

John Couture

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

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Thursday, October 02, 2003 8:52 AM
To: tesla-at-pupman-dot-com
Subject: NST power rating con


Original poster: Thomas <tom-at-pwrcom-dot-com.au>

The more I look into this the more proof I get that the actual power
available from an NST is only half of the face plate values' product, i.e.

P =(V x I)/2

It's the only way I could get this to work out:

http://www.users.bigpond-dot-net.au/broken.trout/Rotary_eqns.pdf

Also it gives an extremely close value (+10%err) for spark length when half
the secondary VA is used for P in: L = 1.7sqrt(P) for my coil.

I think the +10% length measured is due to the primary cap being resonant
with the NST, and a slightly too wide spark gap.

Why is this con(fidence trick) by NST manufacturers not mentioned on any
Tesla coil design web sites (that I've seen)?

It's almost as bad as the *peak music power* con used by cheap audio gear
manufacturers.

Tom L.