Re: Input power measurement

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

Original poster: "Skip Greiner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <sgreiner-at-wwnet-dot-com>

Hi Bart and Gary

The 9/120 NST that I described in my original post is a standard unit still
in its original case. It draws 17A when running in resonant mode. At least
that is what the iron vane meter reads. I have "calibrated" the meter using
a 1600W resistance heater and the reading is dead nuts.
Skip

-----Original Message-----
From: Tesla list <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Tuesday, March 11, 2003 6:52 AM
Subject: Re: Input power measurement


 >Original poster: "Barton B. Anderson by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <classictesla-at-netzero-dot-com>
 >
 >Hi Gary,
 >
 >You know, your right. I was trying to talk about the resonant condition
 >just a little, but mainly to point to Richie's site. I should not have
 >stated that this was the cause to the high current draw. I mainly wanted to
 >point out the maximum current "characteristic" of a resonant circuit (which
 >of course is true). Actually, what I said in that first line is just
 >opposite of what it should say. When the cap is resonant, we cancel
 >reactance's to a large degree and by doing so, we actually "reduce" the
 >current draw required to charge a cap to x-voltage, thus decreasing the
 >charge time. It's the maximum current characteristic of resonance that
 >allows this. As we move off resonance (either direction), reactance's feed
 >back into the line. This opposes and we need more current if we are to
 >charge the cap in the same time frame. So if Skip moved off a resonant cap
 >size, he will probably see a larger current draw.
 >
 >I agree that the face plate rating is not the limit and really isn't for
 >most transformers unless poorly designed. That point probably vary's for
 >each NST manf., size, and model. Skip had 17A, which for a modified NST,
 >isn't all that surprising. It's the removal of shunts that is the probable
 >cause for the higher current. Can't be the cap size. If he were to move
 >towards LTR, the draw would increase, however, he may be near saturation
now.
 >
 >Thanks and take care,
 >Bart
 >
 >Tesla list wrote:
 >
 >>Original poster: "Lau, Gary by way of Terry Fritz <teslalist-at-qwest-dot-net>"
 >><Gary.Lau-at-hp-dot-com>
 >>
 >>I don't think that the cap being mains-resonant results in the maximum
 >>current draw.  With my 15/60 NST, I've noted OK performance with a
 >>mains-resonant 0.01uF cap, better-still performance (and comparably higher
 >>mains current) with a 0.02uF cap, and unstable performance with
 >>breaker-popping current draw with a 0.03uF cap.
 >>
 >>It appears that when driving a Tesla Coil load, the faceplate rating on an
 >>NST is irrelevant, grossly understating the maximum possible VA draw.  I
 >>"think" it has to do with a near-resonant mains condition of the NST
 >>secondary and the tank cap.  If you have a LTR cap trading energy to the
 >>NST, a larger cap will dump more energy into the NST, resulting in a
 >>higher secondary current, saturating the current shunts.
 >>
 >>Gary Lau
 >>MA, USA
 >>
 >>  -----Original Message-----
 >>From:     Tesla list [mailto:tesla-at-pupman-dot-com]
 >>Sent:    Sunday, March 09, 2003 1:32 PM
 >>To:    tesla-at-pupman-dot-com
 >>Subject:    Re: Input power measurement
 >>
 >>Original poster: "Barton B. Anderson by way of Terry Fritz
 >><teslalist-at-qwest-dot-net>" <classictesla-at-netzero-dot-com>
 >>
 >>Hi Skip,
 >>
 >>Resonant mode running is causing the high charging current. The cap value
 >>is designed to be resonant with the transformer at mains frequency
 >>(charging frequency). At resonance, LC reactances are ideally removed and
 >>leave only the winding resistance in the circuit. Thus, a maximum current
 >>characteristic is achieved (which is the purpose of running in a resonant
 >>mode). Richie Burnett has a good write up of this (sometimes ok, sometimes
 >>not).
 >>
 >>http://www.richieburnett.co.uk/resonant.html#resonant
 >>
 >>Take care,
 >>Bart
 >>
 >>Tesla list wrote:
 >>
 >> >Original poster: "Skip Greiner by way of Terry Fritz
 >> ><teslalist-at-qwest-dot-net>" <sgreiner-at-wwnet-dot-com>
 >> >
 >> >Hi all
 >> >I am using a 9kv at 120ma NST. In operation I use an iron vane ammeter
 >> >(known to be within 5% accuracy) to monitor current. My mains voltage is
 >> >nominally 117V. Interestingly the current into the NST is about 17A when
 >> >running in resonant mode. It is my understanding that an iron vane meter
 >> >reads true input current regardless of waveform. Therefore my input
power to
 >> >the NST is nearly 2000 watts.
 >> >
 >> >I would appreciate comments from anyone who can help explain the
discrepancy
 >> >between the 1080va rating of the "current limited NST and the measured
input
 >> >in resonant mode operation.
 >> >Skip
 >> >
 >> >
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