# Bilifar coil inductor

1. Apr 28, 2012

### nemesiswes

I have a question about a bilifar coil. First I need to set the image,

You have a opposing bilifar coil so as to decrease the inductance of the coil.
http://en.wikipedia.org/wiki/Bifilar_coil

1 Winding will be coil A and the other coil B just so we can all know which coil turn we are all talking about.

Now the question I have is what happens when you power up the bilifar coil to steady state and then shut down, let's say coil B? What happens to coil A?
I believe that Coil A will have a temporary Voltage increase since Coil B would be inducing a voltage opposite it's own voltage.
What effect will Coil A's own inductance have on it's self since as coil B is decreasing , coil A's inductance should be increasing until Coil B is fully off.
Would this inductanc increase somehow lower Coil A's voltage and thus current and thus it's total Magnetic field porduced, it is already at steady state though and no long powering up?

2nd part of the Question is:

What happens to Coil B when it powers back up again, I mean what inductance would it encounter.

Would Coil B's inductance be that of coil B as if it was just a single coil without coil A?
or
Would Coil B's inductance be what is was before when both Coil A and B were powering up, very little because they are opposing each other?

For the 2nd Part or the question, I am not sure what will happen, or the first part for that matter. I think that since Coil A is still on and producing an opposing field to Coil Bs, that coil b's inductance would still be very little and allow it rise to steady state much much faster than if was seperate and there was no coil A creating a opposite Magnetic field.

2. Apr 28, 2012

### jim hardy

A question well stated is half answered.

I think you need to spend some time formulating your question.

3. Apr 28, 2012

### nemesiswes

Well I can't think of any simpler way to explain the question, if you read it all the way through it should be pretty straight forward. Then again maybe it is just me that it seems straight forward to and no one else, lol

4. Apr 28, 2012

### jim hardy

can you define what you mean by:

"opposing bifilar coil" , i didnt find it on the wiki page

"power up the bilifar coil to steady state "

"and then shut down"

"Coil A's own inductance "

well i need an interpreter !

Maybe somebody else can parse it.

You might print it out and see if it looks same on paper as it does on the screen. I do that a lot to clarify my wording .

old jim

5. Apr 29, 2012

### nemesiswes

Oh ok, I see where you might get mixed up now, sorry.

"opposing bifilar coil"

I meant that because a bilifar coil is composed of two opposing turns of wire wrapped around the same core, there is one turn that opposes the next turn and so, just like it says on the wiki page for opposing bilifar coils used to create a low inductance coil ( usually wire-wound resistors). Sorry, I can see how that would be confusing, lol, It made it sound like I was talking about two separate bilifar coils.

"power up the bilifar coil to steady state "

I mean exactly that, apply power to the bilifar coil, since the coil would have two separate wire turns all on the same core that are wound in such a way that the magnetic field of each is canceled out, You would actually be applying power to two separate coils, just there are both on the same core, you would apply power in one direction for one of them and the opposite direction for the other.

"and then shut down"
Well there was more to it
"and then shut down, let's say coil B? What happens to coil A? "
I mean pretty much what it says at the end. What happens to coil A if you shut down coil B since they are both on the same core and produce opposing magnetic fields, what happens to coil A when coil B is shut down?

"Coil A's own inductance "

I mean Coil A's self inductance, since Coils b is decreasing in power and so is it's magnetic field, what effect will Coil A's self inductance have on itself. When coil B was on and opposing Coil A's Magnetic field, this caused Coil A's inductance to drop from what it would normally be if it was separate from Coil B, like if you placed them on two different cores and far away from each other so they had no effect on eachother.

Sorry for the confusion, lol. I hope this helps to understand what I am trying to ask.

6. Apr 29, 2012

### Bob S

The main reason for a bifilar-wound coil is to maximize the coupling between primary and secondary windings, especially at higher frequencies. I think it also minimizes stray fields.