Suppose if I have 2 coils that are identical with same value of inductance and interconnect them on the same core, is it possible to get net inductance as zero?

 

Yes, it is called a bifilar coil or bifilar winding.

You can create a low inductance resistive load by folding the wire in half and then winding it on the core as show in the diagram:

 

0.000 - no. Close to zero - yes. Many wire-wound resistors are available with a "non-inductive" construction. A telephone hybrid transformer uses opposing windings to prevent energy transfer, a form of inductance cancellation.

For a non-inductive resistor, the resistance wire is wound in one direction around a ceramic core for half the length of the core, then the direction of rotation is reversed and the wire is wound in the other direction for the rest of the core. A ceramic core is not the same as a magnetic material, so the effect is two air-core inductors of the same size but opposite winding direction, in series.

ak

 

Suppose if I have 2 coils that are identical with same value of inductance and interconnect them on the same core, is it possible to get net inductance as zero?

Hello,

What do you mean by 'net' inductance, where do you intend to make the measurement?

Assuming you have two equal coils you can either connect them in series or in parallel, and wind them series aiding or opposing.

If you measure the total inductance then the following...
If you connect them in series and wind them series opposing, then the inductance as well as the current will drop to close to zero.
If you connect them in parallel and wind them opposing, then the inductance as well as the voltage drops to near zero.

If you measure the inductance between the two windings then the best way is bifilar. That would be considered mutual inductance and it would drop as low as you can get it with a simple structure.

 

Hello,

What do you mean by 'net' inductance, where do you intend to make the measurement?

Assuming you have two equal coils you can either connect them in series or in parallel, and wind them series aiding or opposing.

If you measure the total inductance then the following...
If you connect them in series and wind them series opposing, then the inductance as well as the current will drop to close to zero.
If you connect them in parallel and wind them opposing, then the inductance as well as the voltage drops to near zero.

If you measure the inductance between the two windings then the best way is bifilar. That would be considered mutual inductance and it would drop as low as you can get it with a simple structure.

I meant that if I connect two equal inductors (say both are 5 mH) in series opposing manner and I want to measure the net inductance of the combination.

 

I meant that if I connect two equal inductors (say both are 5 mH) in series opposing manner and I want to measure the net inductance of the combination.

If the magnetic fields of the two coils are not interacting (physically distant), the two individual inductors will simply add and not care about the other inductor.

 

If the magnetic fields of the two coils are not interacting (physically distant), the two individual inductors will simply add and not care about the other inductor.

And please correct me if I'm wrong, but if you connect two inductors in series, it won't matter if their coils have different orientation, i.e. one is left-wound, and the other one is right-wound.

 

Suppose if I have 2 coils that are identical with same value of inductance and interconnect them on the same core, is it possible to get net inductance as zero?

hmmm...why use inductors if you don’t want inductance...

 

I meant that if I connect two equal inductors (say both are 5 mH) in series opposing manner and I want to measure the net inductance of the combination.

In order for "opposing manner" to have any meaning, the magnetic fields of the two inductors must interact to create mutual inductance. If these are physically separate inductors, then you are going to have a very hard time getting a really high coupling coefficient. But to the degree that you do, you will lower the net inductance. Putting them on the same core will help.

 

hmmm...why use inductors if you don’t want inductance...

May need the coil but don't want the inductance -- wire wound resistors are the obvious example.

 

Yes, it is called a bifilar coil or bifilar winding.

You can create a low inductance resistive load by folding the wire in half and then winding it on the core as show in the diagram:

There's always a bit of parasitic - but that's the standard way for lowest possible inductance.

 

I meant that if I connect two equal inductors (say both are 5 mH) in series opposing manner and I want to measure the net inductance of the combination.

Hello again,

Taking your statement at face value, if you have two inductors of equal measured value L1 and connect them in series, then the inductance is:
Ltotal=2*L1

 

May need the coil but don't want the inductance -- wire wound resistors are the obvious example.

Ok...but then you want a resistor.

 

Ok...but then you want a resistor.

Yes, but you are using an inductor (what you asked) to get it even though you don't want the inductance.

 

Yes, but you are using an inductor (what you asked) to get it even though you don't want the inductance.

umm..no...you are using a resistor that happens to have inductance...

 

Then this is this Moebius Resistor that is noninductive.



Non-Inductive Resistor

 

Ok...but then you want a resistor.

This is exactly what a wire wound low inductance resistor is. Yes, in this case, you want a resistor. High power so it is wound with resistive wire. But a lot of times you don't want the inductance that would come with it if it was just a straight wind.

 

Hello again,

Taking your statement at face value, if you have two inductors of equal measured value L1 and connect them in series, then the inductance is:
Ltotal=2*L1

What about the mutual inductance between them?
Theoretically, it would be something like this based upon the formula.


But practically, inductors don't have zero resistance and hence I was wondering whether net zero inductance is possible.

 

To have inductance cancelling out both coils must share the same magnetic field. If the don't, then the inductance add. And net zero inductance is probably close to Impossible as any trace or lead has some inductance. But practical zero inductance for each application is possible. It just depends on how fine you want to split hairs
And resistance of an inductor is not inductance.

 

hmmm...why use inductors if you don’t want inductance...

Just for thoughts. I am just thinking whether its possible or not. Like when I saw those equations and substituted the same L values and got zero, I was just wondering whether its possible. I am not building something out of it in a lab.