Re: [TCML] NST Measurements

[sparktron01@xxxxxxxxxxx]

Bart

Is it possible that the inductance varying is hosing the apple cart?

Instanteous voltage for an inductor (complete) is:
V = iR + L (di/dt) + i (dL/dt)

The last term in "linear" circuits tends to zero and (usually) has
no bearing on circuit.  But with a magnetically shunted circuit
the third term starts influencing the second, and vice versa
(i.e the whole circuit becomes VERY non-linear...)

Regards
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA. USA
 -------------- Original message ----------------------
From: bartb <bartb@xxxxxxxxxxxxxxxx>
> Hi Gary,
> 
> This average ratio I was looking at is not working. I used a second 
> 15/30 to power the test NST measuring HV up to 17kV output open circuit. 
> I started at 1250V in and the average ratio then was high (200 falling 
> down to 160 as voltage was increased). The numbers I received were 
> simply coincidental at the low 124V feed I guess (funny how that seems 
> to happen more times than it should).
> 
> Back to the drawing board.
> 
> Even with primary feeds and secondary measurements, only at 10V input 
> did the turns ratio equal the rated Vout/Vin. Below and above this 
> value, it varied. However, in the data below which is all measured, I 
> show the ratio's and although it goes above the rated value of the 
> transformer (in open circuit), it is not overly high when actually measured.
> 
> Using methods like feeding the secondary is not working out (yet). As 
> you can see, I was looking at low voltages, but I never went below 10V. 
> When I did, the ratio just kept falling, so that upsets my apple cart. 
> Everything else is strait forward, but the turns ratio measurement is 
> not (quite the opposite of what I took for granted). Neat problem to 
> solve. I think these shunted transformers are a bit more complex than 
> anyone assumes. If we know the transformer ratings, were ok, but if not, 
> then large error is probable.
> 
> Feed     Meas.
> Pri      Sec      Ratio
> -----    -----    --------
> 10.0     1250     125.00
> 20.1     2680     133.33
> 30.0     4130     137.67
> 40.2     5590     139.05
> 50.1     7030     140.32
> 60.0     8380     139.67
> 70.1     9770     139.37
> 80.0     10970    137.13
> 90.0     12350    137.22
> 100.2    13550    135.23
> 110.3    14850    134.63
> 120.2    16390    136.36
> 130.0    17120    131.69
> 
> Take care,
> Bart
> PS. Anyone know any Neon Sign Transformer engineers?
> 
> 
> bartb wrote:
> > Hi Gary,
> >
> > I have done this, but not checked it. So, I did just now. The 15/30 
> > measured 175X at 124.2Vin. So this presents a possible large error 
> > depending on where the input is in the stream.
> >
> > I believe we should be looking at both sides equivalently. If you feed 
> > 120V to sec and measure 0.784V at the primary, you should then feed 
> > 0.784V (or as near as you can get) to the primary and measure the 
> > secondary. Take the both ratio's and average. So I checked this.
> >
> > Measurements of my 15/30:
> >
> > Feed sec = 124.2V, pri = 0.708V = ratio of 175.4
> > Feed pri = 0.76V, sec = 55.0V = ratio of 72.4
> > Average (72.4 + 175.4) / 2 = 124 turns ratio (125 expected)
> >
> > Decent considering meter error (and using a single meter). I'll try to 
> > go through this at various voltages to see how it plays out.
> >
> > Gary, can you confirm on your NST's? If this works out decent on your 
> > NST's, then it's an easy procedure to ensure turns ratio accuracy as 
> > well as inductance ratio on transformers with no data (or confusing 
> > data).
> >
> > Thanks for looking at that.
> > Bart
> >
> > Lau, Gary wrote:
> >> Hi Bart,
> >>
> >> As often as I have dispensed the same advice to measure and feed the 
> >> mains voltage into the NST secondary and measure the primary to 
> >> determine the sec/pri ratio, I don't recall ever having actually done 
> >> that to mine.  So, I just pulled out a 15/30 and a 15/60 NST. 
> >> The 15/30 measured a ratio of 153X, so assuming a 120V primary, 
> >> predicts a 18.3kV secondary.
> >>
> >> The 15/60 measured a ratio of 145X, so assuming a 120V primary, 
> >> predicts a 17.4kV secondary.
> >>
> >> The meter that I used is a simple Fluke DMM, not RMS.  But given that 
> >> the NST is going backwards, I wouldn't think that it's getting near 
> >> saturation and the associated waveform weirdness.  Unfortunately I 
> >> don't own a HV probe that I would trust to measure it in the normal 
> >> operating sense.  Have you done this and gotten closer to the 
> >> faceplate voltage rating?
> >>
> >> Regards, Gary Lau
> >> MA, USA
> >>  
> > _______________________________________________
> > Tesla mailing list
> > Tesla@xxxxxxxxxxxxxx
> > http://www.pupman.com/mailman/listinfo/tesla
> >
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla

_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla