User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:24.0) Gecko/20100101 Thunderbird/24.3.0
On 3/19/14 6:05 PM, alfred erpel wrote:
Hello All,
I am preparing to wind a flat spiral coil using stranded steel cable.
The steel cable is galvanized and has a .030 thick vinyl coating.
(this may be used for a choke or other purposes at 60hz, but NOT as a
primary in a tesla coil).
Steel is pretty high resistance compared to copper, but if your
application isn't using a lot of power, this might not be an issue.
It is 7x19 cable measuring .125 diameter
without the insulation. The 7 part of the "7x19" means there are 7
big wires, one in the middle with 6 wires twisted around it. The 19
part of the "7x19" means each of the 7 wires is comprised of 19
really small wires twisted together. The seven big (composite) wires
are rotating clockwise down the wire. Each of the 7 wires has the 19
wires rotating counter-clockwise. See this image for the cross
section which I just explained above.
http://www.steelwirerope.com/images/Constructions%20Images/General%20Purpose%20Ropes/MainImages/7x19Main.jpg
question 1: I want maximum induction from my flat spiral. Can it be
determined from the information provided whether to wind clockwise or
counterclockwise? Also, this If so, please explain.
Makes no real difference. The weaving in and out of the spiral strands
relative to the overall big coil is a very small effect.
question 2: [not related to example described above] If someone were
winding a flat spiral primary with 10 gage stranded copper wire
created with ALL the strands wound clockwise, would the resultant
inductance be affected by whether way the flat spiral coil was wound
clockwise or counterclockwise?
Nope. at least not that you could measure.
Here's a gedanken experiment: say your 10AWG wire were a flat ribbon
cable like zip cord or Romex with 2 strands, and and say you are winding
a flat spiral with 10 turns that is 20" in diameter (so the turns are 1"
apart. You could wind your flat spiral two different ways:
First, with the long axis of the ribbon parallel to the axis of the
spiral (the easy way to wind it).
The inductance of the two strands, individually, are identical: they're
the same distance from the center, etc.
Now wind that coil with the long axis of the ribbon cross section
perpendicular to the coil's axis (this is the hard way).. that whole
think lays flat. Compare the inductance of the two windings. They'll
be slightly different, because one has a slightly smaller overall
dimeter, and all the turns are slightly closer to the inside. But it is
a small difference.
Now imagine you wind that coil with the ribbon cable twisted. Each
strand spends about the same amount of distance from the center as it
moves in and out. So all the strands will be the same inductance.
