Re: Input power measurement

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

Original poster: "Barton B. Anderson by way of Terry Fritz <teslalist-at-qwest-dot-net>" <classictesla-at-netzero-dot-com>

Hi Skip,

Yes, understood. The shunts removed was another post (sorry). So, a cap 
resonant to the transformer and no modifications and we would expect to see 
about 9 to 10 amps but your measuring 17A, correct? And measuring with an 
iron vane meter (true RMS). Have you ran a cap size off of resonance? Have 
you checked an inductive load like a motor against the meter with say any 
other meter?

Sorry for my lack of thought on this one - it's been "one of those" weeks. 
On a brighter note, my new pc board at work tested out perfectly. I think I 
had that on my mind all week among a few dozen other things. One of those 
deals where you have to make several trace routing changes just prior to 
ordering 1000 pcb's! (I fail to understand how anyone can order 1000 pcb's 
and hope it works - talk about being set-up to fail - "they" and I got 
lucky this time). Anyway, after wiping off the sweat from my brow, maybe I 
can engage think with a clearer head.

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 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
> >> >
> >> >
> >> >
> >> >
> >>
> >>
> >>
> >>
> >
> >
> >
> >
> >
>
>
>
>