[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

RE: NST power rating -- another perspective



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


John F. -

When I tested the NST with only a capacitor load the input wattage was very
low as would be expected for a reactive load. The NST was 7.5KV, 30 ma, 225
watts.

For .00267 uf load
Input V=120  A=1.08  VA=129.6  W=20  PF=15.4
Output V=5000  ma=8.4  VA=42
Note that input VA > output VA

For .01623 uf load
Input V=120  A=0.80  VA=96  W=50  PF=52.1
Output V=6600 ma+36.5  VA=240.9
Note that input VA < output VA

I tested several other sizes of capacitors. The tests gave me data for
several types of curves. For example I made a graph showing two curves, one
for input VA and one for output VA. The two curves crossed at about 0.0088
uf and gave the opposing VA conditions shown above.

I don't understand how you can get a high wattage input or output if the
load is only a capacitor. The joules (energy) in a  capacitor would normally
be returned to the source with little wattage loss. Are you referring to TC
operation which is a different test setup? The non-current limited
transformer with a spark output is another story.

The 25% maximum output is only for a NST with  varying resistor loads and is
an important test for NST operation only and is not a TC operation. This is
a simple but instructive test that should be familiar to all coilers. The
tests for Tesla coil operations are a different group of RCL load tests.

John Couture

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



-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Tuesday, October 14, 2003 1:33 AM
To: tesla-at-pupman-dot-com
Subject: Re: NST power rating -- another perspective


Original poster: FutureT-at-aol-dot-com

In a message dated 10/13/03 12:43:22 PM Eastern Daylight Time,
tesla-at-pupman-dot-com writes:

 >When a coiler tests a NST with different resistance loads he will find that
 >the maximum wattage output that he will get from the NST will be about 25%
 >of the nameplate rating on the NST. The reason for this is that as the
 >resistance is reduced the NST current  increases but the output voltage
 >decreases (to zero). The output power (watts) will be the product of
current
 >times voltage and will never be more than about 25% of the nameplate
rating.
 >Coilers who say that their NST is producing 50% of nameplate watts output
 >are not metering their systems correctly. It is obvious the maximum power
 >theorem does not apply to NST's. The power  transformers that are not
 >current limited are another story.


John,

When using NST's with a capacitive load as in a Tesla coil, it appears
to me that the NST can supply approximately its rated wattage output
without over-volting the NST input.  I'm basing this on measurements I did
of the peak capacitor voltage and capacitance, which permitted me
to calculate the joules, and then the output "wattage" based on the
breakrate.

Another test which supports the above statement is that comparisons
with non-current limited transformers gave a similar spark length for a
similar input power to that of the NST.

When you speak of the 25% of rated output capability of an NST,
are you saying this is true for TC usage?

John