Windings vs Diameter
Date: Thu, 29 Jun 2006 23:28:07 -0600
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Windings vs. Diameter
Original poster: Vardan
<vardan01@twfpowerelectronics.com>
Hi,
Just for the record...
The coil I just wound:
http://drsstc.com/~sisg/files/SISG-coil/P6290127.JPG
is 11.50 long with #30 wire. There are 985.00 turns on it via digital counter.
The wire is 0.0116 inches in diameter via a new Starrett 436 micrometer.
985 x 0.0116 = 11.426 inches. Pretty close ;-)) I pushed the wire with a
finger nail all the way during the wind so it is tight and the wire torque was
high. The wire is "cheap" and had a few rough spots
I could feel as it was going out my fingers.
There is a "wiring percentage" number of 91% for this wire that seems all
wrong...
If you can measure the wire diameter really well and wind it tight and forced,
the "wire diameter x turns" seems to work out just fine... Thin wire like this
forces more easily than thicker...
Cheers,
Terry
Date: Fri, 30 Jun 2006 15:03:11 -0600
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Windings vs. Diameter
Original
poster: Vardan <vardan01@twfpowerelectronics.com>
Hi Curt,
When wire is wound it tends to twist and roll some leaving spaces between the
windings so there are a lot of charts around that predict how much space that
is.
Page 8 below is a very common chart that lists #30 wire at 90.5 Turns Per Inch.
http://hot-streamer.com/temp/FormulasForTeslaCoils.pdf
Here is the Nexans chart:
Winding percentages:
AWG %
10-11 99
12-13 98
14-15 97
16-17 96
18-19 95
20-21 94
22-23 93
24-28 92
29-33 91
34-38 90
39-42 89
43 88
Of course, when I started the wind and could see this space, so I used my finger
to force them together. If I had not done that then the chart might have been
very good!! But it looks like I was able to push out "all" the space between
the windings. 99.9999% of the coils on earth are machine wound so the chart is
probably fine.
However for Tesla coil secondaries, we almost always do them by hand so there
can be significant differences in turns per inch. We run into the problem when
trying to predict secondary inductances using standard turns per inch charts.
There is also a significant variation in wire coating thicknesses. I never had
a good feel for how much this variation could be until now. it can probably
make a 20% difference in the secondary coil inductance!!
Hardly anyone ever really "counts" the turns exactly, so we always have to
guess... I knew that there was a lot of variation but know I know "why" *:-))
The next time I have to figure out someone's
secondary coil, I will add this to the questions I ask ;-)) If they just let
the wire fall naturally, then the chart above is good. If they pushed the
windings together, then it is a pure wire diameter x
distance thing. And that is a big difference!!
Cheers,
Terry
Date: Fri, 30 Jun 2006 19:55:08 -0600
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Windings vs. Diameter
Original
poster: "Jon Danniken" <danniken@comcast.net>
> Hardly anyone ever really "counts" the turns
exactly, so we always
> have to guess...
Hehe, I actually use a reed switch with a magnet to switch a counter to count
out my windings. Probably overkill, but the counter was cheap enough at the
time when I bought it from the local (now gone, sadly) surplus shop.
Jon
Date: Fri, 30 Jun 2006 19:55:53 -0600
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Windings vs. Diameter
Original
poster: "Peter Terren" <pterren@iinet.net.au>
To get my turns estimate, I usually place a piece of paper on the coil and run a
pencil over it. This gives a tracing of each turn and makes it easy to place
flat on a table in good light with a ruler to
count turns per inch, to whatever precision you want. eg 19G wire is .0335 in
diameter by my micrometer. Over 2 inches on my 4 inch coil there are 58 turns
ie .0345 inches /turn. Gives a wiring percentage of 97% which is "better" than
machine wound 19G of 95% by your table.
Peter
http://tesladownunder.com/
Date: Sat, 01 Jul 2006 16:39:24 -0600
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Windings vs. Diameter – errors
Original
poster: Vardan <vardan01@twfpowerelectronics.com>
At 07:05 PM 6/30/2006, you wrote:
>To get my turns estimate, I usually place a piece
of paper on the
>coil and run a pencil over it. This gives a
tracing of each turn
>and makes it easy to place flat on a table in
good light with a
>ruler to count turns per inch, to whatever
precision you want. eg
>19G wire is .0335 in diameter by my micrometer.
Over 2 inches on my
>4 inch coil there are 58 turns ie .0345 inches
/turn. Gives a wiring
>percentage of 97% which is "better" than machine
wound 19G of 95% by
>your table.
>Peter
>http://tesladownunder.com/
Neat idea!! I have also put marked tape on coils and taken high res digital
photos. Blow them up on the computer in a graphics program to mark off the
turns... But easier still just to count them in the
first place ;-))
The new little coil measures 17.41mH.
It measures:
985 turns (exact)
2.992 inches in diameter of the form but not with the wire diameter added (#30
at 0.0116 inches in diameter via a new Starrett 436 micrometer.)
11.50? long
That works out to.... r = 1.4989... 16.965mH by Medhurst.
So the wound coil is 2.6% over Medhurst predicted. That is vastly better than I
have ever guessed before ;-))
If we assume I made an error in the diameter, it would work out to 3.042 inches
which is far inside what I can measure. So I might be seeing the Medhurst
formula's error now ;-))
MandK gives 17.06422mH which is only 2% low. But the "other" meter (I don't
normally trust it) "matches" that at 17.06mH... So probably all down in the
measurement noise errors now... I have "standard" caps somewhere...
But I think "I know the details" for such things now ;-)) Coils that have their
turns "packed or not packed" is a big deal.
Cheers, Terry
Date: Sat, 01 Jul 2006 16:43:05 -0600
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Windings vs. Diameter
Original
poster: "Barton B. Anderson" <bartb@classictesla.com>
Yep, I to use a counter and proximity switch.
Bart
Tesla list wrote:
>Original poster: "Jon Danniken" <danniken@comcast.net>
>
> > Hardly anyone ever really "counts" the turns
exactly, so we always
> > have to guess...
>
>Hehe, I actually use a reed switch with a magnet
to switch a counter to
>count out my windings. Probably overkill, but
the counter was cheap enough
>at the time when I bought it from the local (now
gone, sadly) surplus shop.
>
>Jon
Date: Sat, 01 Jul 2006 16:47:14 -0600
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Windings vs. Diameter
Original
poster: Vardan <vardan01@twfpowerelectronics.com>
I converted to a Radio Shack security magnet reed switch too for the turns
counter (don't know part number). It works perfectly ;-)))
http://drsstc.com/~sisg/files/SISG-coil/MagSwitch.JPG
Cheers,
Terry
At 04:06 PM 7/1/2006, you wrote:
>Yep, I to use a counter and proximity switch.
>Bart
>
>Tesla list wrote:
>
Date: Sat, 01 Jul 2006 18:25:26 -0600
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Windings vs. Diameter – errors
Original poster: Vardan
<vardan01@twfpowerelectronics.com>
Just to follow up...
My new coil's "official numbers" are:
Diameter 3.000 inches (center to center of wire) (Starrett #120A-6) Wire
diameter 0.0116 with insulation (Starrett #436-1) 985 turns (electronic counter
during winding) 11.500 inches long (Starrett #120-12) Lexan coil form with
Envirotex coating. Lexan end caps with none ferrous end terminals.
DC resistance (HP34401A) = 83.30 ohms
Medhurst inductance = 16.988mH
MandK inductance = 17.088mH
JAVATC (Ldc)= 17.155mH
B&K meter = 17.06mH
Elenco meter (LCR-1801 very trusted) = 17.40mH
Wavetek 37XR = 17.35mH
HP 33120A, 34401, TEK TDS312, Standard cap = 17.47mH
I'll go with the Elenco at 17.40mH since it is always right ;-))
http://drsstc.com/~sisg/files/SISG-coil/CoatedCoil.JPG
At 300kHz, I am getting in Rac of 196 ohms "in series" with the 83.3 ohms of DC
resistance for a total of 279 ohms. MandK predicts 238 ohms, but I am not sure
if that is total resistance or just the AC part. But there are a lot of error
details with this measurement.
Cheers,
Terry
Date: Sun, 02 Jul 2006 11:57:51 -0600
From: Tesla list <tesla@pupman.com>
To: tesla@pupman.com
Subject: Re: Windings vs. Diameter – errors
Original
poster: Ed Phillips <evp@pacbell.net>
One easy way to get a pretty good check on the total wire length is to measure
the DC resistance and divide by the "table values" for resistance of that wire
size. Knowing the wire length, diameter, and the OD of the form you can
calculate the number of turns easily, remembering that the effective turn
diameter is the OD plus the wire diameter. I've found it checks within a
percent or so at the worst. Of course, just counting the turns as you
wind is still the easiest and best way.
Ed
As for "Medhurst inductance", remember that there is more than one approximate
formula, depending on the L/D ratio, and that there are simple and more accurate
formulae readily available. Considering the effective operating bandwidth of our
coils, is great accuracy of any interest other than as a subject unto itself?