On 8/19/2019 9:11 PM, John S wrote:
On 8/19/2019 6:12 PM, amdx wrote:
On 8/15/2019 2:41 PM, John S wrote:
On 8/15/2019 8:46 AM, amdx wrote:
On 8/14/2019 7:11 AM, John S wrote:
On 8/13/2019 9:29 AM, amdx wrote:
On 8/9/2019 8:06 AM, John S wrote:
On 8/8/2019 11:45 AM, amdx wrote:
Hi all,
If you put two coils on one form, but wind one in the opposite
direction, Do the currents flow in opposite directions?

Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* Mikek

PS. opposite winding direction as in clockwise or counter
clockwise,
Â*Â*or like a left hand and right hand thread.

If it is a continuous coil with only two connections (start to
finish) but winding is reversed in the middle of the coil, the
current does not reverse.

Â*Â*That wasn't what I ask, but since I posted I did put an answer
together. It took me several drawing to get to a final answer that
makes it so simple I don't know why I ask the question. I took me
several hours to come to the conclusion though.
Â*Â*My answer to your question would be, the current does reverse
and for your example, the current would be very low. Probably not
zero because of time/phase concerns.

I have one drawing showing a coil and the right hand rule that
gives the answer.

file:///C:/Users/Lamont/Dropbox/contra%20wound%20coil%20with%20flux%20and%20curren t%20flow.jpg



Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* Mikek

The current can not reverse in a series connection. But the magnet
field can reverse in the two series windings if one of the windings
is reverse wound.


Â*Â*I should have added more information.
The coil(s) are put in an electromagnetic field, creating a magnetic
field around the coil. the magnetic field creates a current in each
coil.
what is the direction of each of those currents?
https://www.dropbox.com/s/c4k2hh4syd...0flow.jpg?dl=0


Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* Â*Â*Â*Â* Mikek
PS, it took me hours to get this understood and now, it's like, well
ya!


Ok. You have all the answers so go with that. Good luck.

Â*Â*That answer as stated makes me think you disagree. I would like to
have the conversation. Clearly is was a slog for me an I could easily
have something wrong.
Â*Â* I would say my strongest evidence would be that in order to make
the contracoil measure maximum inductance with a series connection,
you can't just connect the coils in the center and measure from the to
outside ends.
Â*Â*Please let me know what you think.
Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* Mikek

Ok, Mike. Are you familiar with the phasing dots of transformers shown
on some symbols and schematics?

Wind a coil and put a dot at the start of the winding. Wind another coil
in the same direction as the first coil and put a dot at the start of
the second winding:

---.UUUUU----Â* ---.UUUUU----Â*Â* (The phasing dots are periods)

Now connect the two closest ends together, and you get 4x the inductance
of one of the coils if you have perfect coupling.

Now rotate one of the coils 180 degrees and connect the closest ends
together:

---.UUUUU----Â* ----UUUUU.---

If you have perfect coupling, the inductance is zero.

I see no reason the have a contra-wound coil. And you don't have to
actually rotate the coil. By simply changing the connections you can
achieve the same thing as "contra-wound" coils.

BTW transformers and air-wound coils obey the same laws. The difference
between them is coupling factor and core losses.

I may have come to a quicker understanding of this if I had followed
through with the dots convention, but I didn't. Others did mention it.

Ok, you don't disagree with anything I said other than you don't think
it is necessary. In most cases it isn't. But the coils using the
contracoil are very high Q coils for crystal radios. The reduced
capcitance by moving the higher potential difference ends away from each
other raises the Q a few points over a normally wound coil.
As to how much, I don't know. I'm on a little quest to do an experiment
to get an idea. My Q meter only measures to 625 and I expect the Q of my
test coils to be higher, around 1000. To measure that high, I need to be
able to accurately measure a lower drive level on the Q meter (4mV at
0.5MHz to 1.7MHz) . I bought an Hp400E to do that, in fact I bought two.
They didn't agree, so I have sent one in for calibration. I expect to
try some experiments when I get that back.

btw, the coils are 6 inches in diameter on a styrene form wound with
660/46 litz wire.
Thanks for the response, Mikek