On 8/22/2019 5:11 AM, John S wrote:
On 8/22/2019 3:42 AM, amdx wrote:
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.
Â*Â*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.
Â*Â*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.
Â*Â*btw, the coils are 6 inches in diameter on a styrene form wound with
660/46 litz wire.
Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* Thanks for the response, Mikek
Could you measure the Q with a known resistor value in shunt or in
series with the coil (to put in range of your meter) and calculate the
coil's actual Q?
I have been all around the idea of series or parallel resistors in an
effort to measure higher Q, Always some inaccuarcy and non-linerity
shows up very quickly. It has never made any sense! I'm aware of
parasitics and minimize them. I thought it wouldbe simple just install a
1 ohm series resistor, measure Q and then mathmatically back out the
resistor. It never worked. I can not figure out why.
The method I described is well known and works fine and accurately. This
week I was looking through a 1977 Ferroxcube Databook of ferrite
materials, I found a paragraph that even describes the method. It uses
the same HP meter I have and adjust the drive voltage down to 4mV.
I'm using the Boonton 260A, THe Q meter goes to 250. For higher Q's you
reduce the drive form the original 20mV to 10. There is a meter that
reads as multiplier. Full scale is 1x, when you reduce drive so the
meter reads 2X, now you multiply theQ meter by a multiplier of 2.
That meter is only marked to 2.5. That meter is scaled very
non-linearly.So 4mV just barely reads on the scale.
Mikek
Mikek