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Bifilar coil for electromagnet

Posted: Thu Aug 08, 2013 9:46 pm
by samitch26
a patent by tesla uses whats called a bifilar coil to create an electromagnet that has twice the efficency. Has anyone considered this for the polywell device?

Re: Bifilar coil for electromagnet

Posted: Fri Aug 09, 2013 1:02 pm
by mattman
A Bifilar is a winding with two different types of wire. For example, Copper and Aluminum wiring. Both would be clad in some kind of sheathing. Could this winding somehow lower the resistance through the wires?


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I ask, because the main issue with the coils is how much amps you can push through them. We want to drive up the number of Amp-Turns. This means pushing more current through, or, making more wraps of wiring inside. If the resistance drops we can push more amps through. Dan Tibbets, Tom Ligon and others have suggested superconductors as a possible improvement to this issue. They maybe other options, IDK.

Re: Bifilar coil for electromagnet

Posted: Fri Aug 09, 2013 2:27 pm
by DeltaV
Mattman,

You are confusing bifilar with bimetallic.

filar --> filament

BTW, your picture on Wikipedia has one current loop in the wrong direction:

http://upload.wikimedia.org/wikipedia/commons/a/a1/Biconic_Cusps.jpeg
Image

Re: Bifilar coil for electromagnet

Posted: Tue Aug 13, 2013 12:29 am
by samitch26
a bifilar coil, as per the tesla patent, runs two insulated wires in paralell and then connects them in series. You then connect the start of the first wire to the positive and the end of the second wire to the negative of the battery. this then increases the efficiency of the electromagnet.

Re: Bifilar coil for electromagnet

Posted: Wed Aug 14, 2013 8:18 pm
by ltgbrown
Thus making a single strand of wire that folds back on itself?? I am confused.

Re: Bifilar coil for electromagnet

Posted: Thu Aug 15, 2013 4:57 am
by mvanwink5
It is interesting, but for superconductor electromagnets, the reasoning doesn't seem to me to follow. However for test coils where the magnets are pulsed on due to inability to run continuously, it would seem that there is a big advantage. Insulation between adjacent magnet wires would have to be better, so there is that tradeoff. I am not a motorshop man so that would have to be a point of inquiry to him, varnish is not usually intended for high voltage for adjacent magnet wires in the coil, but maybe it would work.
Thanks.

Re: Bifilar coil for electromagnet

Posted: Thu Aug 15, 2013 12:36 pm
by ladajo
ltgbrown wrote:Thus making a single strand of wire that folds back on itself?? I am confused.



Me too.

If you fold a wire back against itself it nulls the field.

I guess I need to go and read the patent. Samitch, it is not clear what you are describing.

Re: Bifilar coil for electromagnet

Posted: Thu Aug 15, 2013 11:32 pm
by KitemanSA
This.
Image

Re: Bifilar coil for electromagnet

Posted: Tue Aug 20, 2013 6:38 pm
by ladajo
So what is the advantage of that over just having twice the turns?

Is it related to voltage droop and making up for that by merging the front half of the winding field with the mid point field?

Re: Bifilar coil for electromagnet

Posted: Sat Aug 24, 2013 6:28 pm
by paperburn1
makes a stronger field if ran in parallel
http://www.magnetricity.com/Bifilar.php

Re: Bifilar coil for electromagnet

Posted: Sat Aug 24, 2013 6:41 pm
by ladajo
what is the advantage of that over just having twice the turns?


I get that, but is it not the same as just having twice the turns? Is it simply a manufacturing advantage?

Re: Bifilar coil for electromagnet

Posted: Sat Aug 24, 2013 7:05 pm
by paperburn1
one long has a higher internal resistance than two short wires, lowers the resistance without reducing the number of coils , makes for a stronger magnet force, the only other option would be to use large wire then your number of turns in a set volume would go down.

Re: Bifilar coil for electromagnet

Posted: Sat Aug 24, 2013 7:11 pm
by ladajo
It still looks like the fields would cancel. I followed the link, and it appears that the winding just loops back on itself. If not, then it is just doubled up (twice the turns).

(e-) enters winding.
loops around in a clockwise right hand twist.
comes to end of coil.
crosses connection,
runs in reverse direction along parallel wire with a left hand twist.
(fields cancel)
pops out second lead back at start.

OR

(e-) enters winding.
loops around in a clockwise right hand twist.
comes to end of coil.
crosses connection,
runs now right to left, but with right hand twist,
(field doubles)
pops out second lead back at start.

OR
(e-) enters winding,
loops around (left to right) clockwise righthand twist.
For twice the number of turns as above but in same length of space, say 6 inches,
(field doubles)
pops out end lead on right hand end of coil.

Where am I seeing this wrong?

Re: Bifilar coil for electromagnet

Posted: Sat Aug 24, 2013 7:16 pm
by ladajo
paperburn1 wrote:one long has a higher internal resistance than two short wires, lowers the resistance without reducing the number of coils , makes for a stronger magnet force, the only other option would be to use large wire then your number of turns in a set volume would go down.


I also get that I can hook up several leads and wrap them in parallel, hook up the ends to the same power source for reduced resistance over one fatter lead.
But the end result is pretty similar, as the current would develop from the same potential, but now split over several leads. It is basic ohms law.
The only advantage I could see is that you potentially reduced the resistance a smidge over single lead, but that would not be a significant difference at the scales we are talking IMO.

I want to get it, but I must be missing some part of the puzzle.

I see this as a simple exercise in parallel verses series circuits.

Is the trick in a center tap? I need to go play with a bit of wire I think.

Re: Bifilar coil for electromagnet

Posted: Sat Aug 24, 2013 7:58 pm
by paperburn1
I remember running two wire in the same direction and close spacing had something to do with increasing the effective force as well, Dagnabit now I am going to have to look some stuff up.