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Re: AC Resistance of wires - was 8 kHz Tesla Coil



Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Thankyou Malcom,

I never did learn how to spell :o))

Gerry R

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>
On 4 Oct 2005, at 5:27, Tesla list wrote:
> Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
>
> Hi Kurt,
>
> The Medhurst resistance tables assume "high frequency" and that the
> proximitry effect is "fully saturated".  The table was also developed
> for coils with a small number of turns (30-50).  The proximitry effect
> may be overestimated.
It should be "proximity" as in "close to".
Malcolm
> Gerry R
>
> >Original poster: "Kurt Schraner" <k.schraner@xxxxxxxxxxx>
> >
> >Hi Bart,Gerry,
> >
> >Medhurst's empirical Method for HF-Resistance of solenoids is
> >implemented in my TC-Plan Excel:
> >http://home.datacomm.ch/k.schraner/TCplan.zip
> >The relevant sheets are "Skineff." and "Proxi-eff.", whose results
> >are transferred to "TC calc."' cells E34:E38. In the light of more up
> >to date, more general methods, Medhurst may soon become of lesser
> >relevance, but I've tried to compare results from it, with Q of some
> >of my coils, estimated from bandwidth measurements at Fres. A summary
> > Excel of the results can be had at:
> >http://home.datacomm.ch/k.schraner/Qsec2.xls or here (view in fixed
> >width font, sorry for the possible mess!):
> >
> >      TC-Secondary Q-Estimation by Medhurst's Empirical Method
> >       for some of my Coils
> >
> >      Geometric Data
> >      Secondary Diameter Length Aspect L/D Turns
> >      Name      [cm]     [cm]     [ - ]    [ - ]
> >      Sk-Seibt   4      150.3     37.58     4187
> >      Sk-UBTT  12.54     60.3      4.81     1680
> >      Sk-5cm    5.11     41.1      8.04      934
> >      Sk-12cm  12.12     58.5      4.83      894
> >      Sk-Long  16.1     140.2      8.71     1976
> >      Sk-20cm  20.52     66.8      3.26      943
> >      Sk-38cm  38.4      44        1.15      346
> >      Sk-B&W *)40.13    177        4.41      813
> >      Sk-B&W *)40.13    177        4.41      813
> >
> >      Geometric Data (cont.)
> >      Secondary Wire-Copper  Pitch Comment
> >      Name        [mm]       [mm]
> >      Sk-Seibt   0.319       0.359 Big error unexplained!
> >      Sk-UBTT    0.319       0.359 Test-signal via low-Z amp.
> >      Sk-5cm     0.4         0.434 no experiment
> >      Sk-12cm    0.6         0.654 Test-signal via low-Z amp.
> >      Sk-Long    0.64        0.71  Test-signal via low-Z amp.
> >      Sk-20cm    0.63        0.708 no experiment
> >      Sk-38cm    1           1.2   cardoard/cotton insul. wire
> >      Sk-B&W *) 1.268        2.177 Test-signal via low-Z amp.
> >      Sk-B&W *) 1.268        2.177 if R Sig-Gen=136 Ohm
> >
> >
> >      Electrical Data
> >      Secondary at1kHz  Fres,bare DC Resist. Wire straigt
> >      Name    Lexp[mH]  exp.[kHz] exp.[Ohm]  with Skineff.
> >      Sk-Seibt 18.13   366.11     114        240.82
> >      Sk-UBTT  66.59   205.4     147.8       147.86
> >      Sk-5cm   5.203   923.8      21.7        n.a.
> >      Sk-12cm  18.2    402.8      21         27.61
> >      Sk-Long  67.7    147.4      55.2       61.05
> >      Sk-20cm  49      202.7      34.8       40.5
> >      Sk-38cm  28.12   217.95      9.2       16.32
> >      Sk-B&W *)54.67   119        14.5       22.3
> >      Sk-B&W *)54.67   119      14.5+136     22.3+136
> >
> >      Electrical Data (cont.)
> >      Secondary Rac-calc. Qexp     Qmedh. Qerror
> >      Name    with Proxy.E  [ - ]  [ - ]    [%]
> >      Sk-Seibt    698.9     156.5  70.8    54.8%
> >      Sk-UBTT     440.65    211.8  186     12.2%
> >      Sk-5cm       n.a.      n.a.   n.a.    n.a.
> >      Sk-12cm     91.01     269    270     -0.4%
> >      Sk-Long     190.6     164.4  168.4   -2.4%
> >      Sk-20cm     128.0      n.a.  478.3    n.a.
> >      Sk-38cm     49.79     104.3  803.7  -670.6%
> >      Sk-B&W *)   44.02     141.7  576    -306.5%
> >      Sk-B&W *) 44.02+136   141.7  141.7    0.0%
> >
> >
> >The method seems to underestimate Q of my small diameter coils, and
> >to (heavily) overestimate the Q of the big diameter coils. What seems
> >obvious is the dominant proximity effect over skineffect for usual TC
> >frequencies, as mentioned before on the relevant treads. Maybe
> >dielectric loss, not considered in the calculations, come to play
> >here...
> >
> >*) For the bandwidth measurements it seems important using a low-Z
> >signal source (--> Terry's low-Z amp), which was not the case for
> >"Sk-B&W". Otherwise the generators internal resistance will reduce
> >measured Q value. Anyway, bandwidth measurements seem prone to higher
> >error, 'cause of amplitude reading on the scope and frequency
> >precision reading from the sig-gen.
> >
> >Well ... my 2cents for the interesting threads about coil Q. If I see
> >coming out a method estimating Q with perhaps 10% error, I'd readily
> >adapt it!
> >
> >Best regards
> >Kurt
> >
> >
>
>
>
>
>