All About Circuits Forum Bifilar Coil Inductance?
 Register Blogs FAQ Members List Today's Posts Search Today's Posts Mark Forums Read

 General Electronics Chat Discussion forum for general chat about anything electronics related, including asking questions about material in the All About Circuits E-book, Worksheets, and Videos.

#1
10-08-2010, 02:12 PM
 wes Senior Member Join Date: Aug 2007 Location: Las Vegas, NV Posts: 242
Bifilar Coil Inductance?

Hello, I have a quick question that maybe someone could answer here.

I know that if you have a Bifilar coil with the winding in a way so that the current goes in the opposite directions then your Inductance of that coil is close to zero (I know it will never reach 0, Impossible )

Now the part I am not sure about has to do with the bifilar coil when wound in series con-fig (I think it is series )

Here is a picture:
http://merlib.org/node/5516

it is the second one.

Would the this configuration have a lower inductance then a standard coil.

My reasoning for this is that since the coils are furthur apart, they would not be affected as much by the current flowing through the coils.

If you follow the flow of the current then you see that it travels withing the coil then exits back out and then goes back into the coil through the second winding?

So would the inductance be smaller or would it be the same as a standard coil or would it be bigger?
#2
10-08-2010, 02:14 PM
 marshallf3 Senior Member Join Date: Jul 2010 Location: Oklahoma City, OK. Large enough to be modern but plenty of country left around it. Posts: 2,358

Good question due to the mutual inductance.

You can compute the inductance of each coil given spacing, etc but two in perfect parallel?
__________________
-
The very first course in engineering school should be how to use Google and Wikipedia
-
I very often misspell or miss things while making posts so come back and double check a few times.
I also have a full time job and often 10 projects going on at the same time so I'm not always online.
#3
10-08-2010, 06:29 PM
 The Electrician Senior Member Join Date: Oct 2007 Posts: 1,722

When you have a bifilar pair like this, you can measure the inductance of one of the coils, ignoring the other; call that value of inductance L.

Now, if the two coils are connected in series aiding configuration, the inductance will be 4*L.

If they are connected the other way, series opposing, the inductance of the combination will be very small.
 The Following User Says Thank You to The Electrician For This Useful Post: observativetiger (02-15-2014)
#4
10-08-2010, 07:40 PM
 Bill_Marsden Super Moderator Join Date: Mar 2008 Location: Dallas, TX (GMT-5 w/ DST) Posts: 19,022 Blog Entries: 5

Which is why it is used to make resistors as opposed to conductors. All wires have some inductance, and by running next to each other, some capacitance. They also have resistance. The method of winding coils determines what characteristic is the predominant one used.

I'm willing to bet this is off a HHO site, because this quote...

Quote:
 Tesla explains that a standard coil of 1000 turns with a potential of 100 volts across it will have a difference of .1 volt between turns. A similar bifilar coil will have a potential of 50 volts between turns. In that the stored energy is a function of the square of the voltages, the energy in the bifilar will be 502/.12 = 2500/.01 = 250,000 times greater than the standard coil!
is utter BS!. A bifilar coil with opposing windings stores no energy, the two opposing coils cancel the ability to store energy out. This is why it is predominately used for resistance. Do resistors store energy?

We have heard the same tired false arguments by all the HHO fans out there before Beenthere put his foot down.

__________________
..
"Good enough is enemy of the best." An old engineering saying, Author unknown.

General info:
If you have a question, please start a thread/topic. I do not provide gratis assistance via PM nor E-mail, as that would violate the intent of this Board, which is sharing knowledge ... and deprives you of other knowledgeable input. Thanks for the verbage Wookie.

Last edited by Bill_Marsden; 10-08-2010 at 08:21 PM. Reason: Added qualification to Bifilar Coil
#5
10-08-2010, 07:47 PM
 kubeek Senior Member Join Date: Sep 2005 Location: Prague, Czech Rep Posts: 3,445

The two coils are not opposing, the current is still circulating clockwise, from A to B. Still I donīt see any point in this configuration apart from some different capacity.
#6
10-08-2010, 07:48 PM
 bertus Administrator Join Date: Apr 2008 Location: Amsterdam,Holland (GMT + 1) Posts: 12,038

Hello Bill,

You are probably right.
Take a look at post #106 of this thread from the energenicforum:
http://www.energeticforum.com/renewa...hematic-4.html

Lets see what beenthere thinks of it.

Bertus
__________________
You don't have to know everything, if you know where to find it.
When you do ask questions, you may look stupid.
When you do NOT ask questions, you will STAY stupid.

It would be nice to have the Timezone ( GMT +/- x ) in the location field in the profile.
(User CP -> Edit Your Details)
#7
10-08-2010, 08:17 PM
 Bill_Marsden Super Moderator Join Date: Mar 2008 Location: Dallas, TX (GMT-5 w/ DST) Posts: 19,022 Blog Entries: 5

Quote:
 Originally Posted by kubeek The two coils are not opposing, the current is still circulating clockwise, from A to B. Still I donīt see any point in this configuration apart from some different capacity.
Look again at the second illustration, one coil is clockwise, the other counterclockwise, thereby canceling the inductance. I'm not sure what the capacitance would be. Overall I think it would have a very complex frequency response.

I thought beenthere would be interested in this thread (there is nothing wrong with it and it violates no rules), so I sent an email pointing it out.
__________________
..
"Good enough is enemy of the best." An old engineering saying, Author unknown.

General info:
If you have a question, please start a thread/topic. I do not provide gratis assistance via PM nor E-mail, as that would violate the intent of this Board, which is sharing knowledge ... and deprives you of other knowledgeable input. Thanks for the verbage Wookie.
#8
10-08-2010, 08:25 PM
 Bill_Marsden Super Moderator Join Date: Mar 2008 Location: Dallas, TX (GMT-5 w/ DST) Posts: 19,022 Blog Entries: 5

Quote:
 Originally Posted by wes Hello, I have a quick question that maybe someone could answer here. I know that if you have a Bifilar coil with the winding in a way so that the current goes in the opposite directions then your Inductance of that coil is close to zero (I know it will never reach 0, Impossible ) Now the part I am not sure about has to do with the bifilar coil when wound in series con-fig (I think it is series ) Here is a picture: http://merlib.org/node/5516 it is the second one. Would the this configuration have a lower inductance then a standard coil. My reasoning for this is that since the coils are furthur apart, they would not be affected as much by the current flowing through the coils. If you follow the flow of the current then you see that it travels withing the coil then exits back out and then goes back into the coil through the second winding? So would the inductance be smaller or would it be the same as a standard coil or would it be bigger?
You got it backwards, the first illustration is a true coil/capacitor circuit, the second has two coils in opposition to each other. I have seen it many times from HHO nuts. Tesla actually invented the first as a super simple way to build a resonant circuit. Components have gotten cheaper, so it is pretty well obsolete.
__________________
..
"Good enough is enemy of the best." An old engineering saying, Author unknown.

General info:
If you have a question, please start a thread/topic. I do not provide gratis assistance via PM nor E-mail, as that would violate the intent of this Board, which is sharing knowledge ... and deprives you of other knowledgeable input. Thanks for the verbage Wookie.
#9
10-08-2010, 09:51 PM
 timrobbins Senior Member Join Date: Aug 2009 Location: Melbourne, Australia Posts: 318

Have another close look at the winding config guys, and the comment from Tesla - and think about what Tesla was up to!

His bifilar arrangement is configured to purposefully give the opposite 'low inductance' effect that you guys are thinking of.

Imagine applying a step voltage across one of the wires only, and what is generated across the other wire. Analogous to an automotive ignition coil.

Ciao, Tim
#10
10-08-2010, 10:23 PM
 kubeek Senior Member Join Date: Sep 2005 Location: Prague, Czech Rep Posts: 3,445

Quote:
 Originally Posted by Bill_Marsden Look again at the second illustration, one coil is clockwise, the other counterclockwise
I think you should look again, both coils are clockwise.
Attached Images
 patent.jpg (206.7 KB, 16 views)

 Tags bifilar, coil, inductance

 Related Site Pages Section Title Textbook Tesla polyphase induction motors : Ac Motors Worksheet Step-up, step-down, and isolation transformers Worksheet Mutual inductance Worksheet Inductors Worksheet Inductance Textbook Mutual inductance and basic operation : Transformers Textbook Special transformers and applications : Transformers Video Lecture Inductors (Part 1) - Inductors,Capacitors,Transformers Textbook CMOS 555 LONG DURATION FLYBACK LED FLASHER : 555 Timer Circuits Textbook Inductor commutating circuits : Diodes And Rectifiers

 Similar Threads Thread Thread Starter Forum Replies Last Post Suzukiman The Projects Forum 156 06-17-2011 07:19 PM Sirisian The Projects Forum 4 05-15-2010 03:22 PM electricme The Projects Forum 2 10-15-2008 02:21 PM mentaaal Homework Help 9 12-31-2007 01:32 PM Parthasarathy General Electronics Chat 2 02-17-2004 01:25 PM

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Electronics Forums     General Electronics Chat     The Projects Forum     Homework Help     Electronics Resources Software, Microcomputing, and Communications Forums     Programmer's Corner     Embedded Systems and Microcontrollers     Computing and Networks     Radio and Communications Circuits and Projects     The Completed Projects Collection Abstract Forums     Math     Physics     General Science All About Circuits Commmunity Forums     Off-Topic     The Flea Market     Feedback and Suggestions

All times are GMT. The time now is 10:09 PM.