dual inductor on a ferrite core

[frankyengtips]

Hi All,
I am new here. I don't have much EE background so bare with me.
I am trying to build a dual inductor on a ferrite core. I hope this is the correct terminology. Basically I have a rectangular ferrite core and want to inductance produced. So my thinking is it should have 2 windings, each at the desired inductance value. So one I want in the uH range and the other in the mH range.

One of my first step is to wind the core with some wire, 20 turns. It crated 2 rows. I tried to make the wires tight between each turn. I put duct tape between each row to hold the windings. After I measrured the inductor and was able to measure 40uH. One test I wanted to do was to see if the inductance changes if i placed it near another metal (i.e copper, or nickel). Well, the inductance didn't change. I have an inductor that I purchased from the electronic store and that one changed inductance when I put a metal on it or near it.

What could be wrong? Could be it the wire has duct tape on it? Could it be the wire I am using, magnet wire? Please help.
thanks

 

[Skogsgurra]

It isn't easy to understand what you are saying. Or trying to do.
A few questions:

1. Is it a slab of ferrite? Or is it a square core (like an E I core or similar)?
2. Are two windings supposed to be active simultaneously? Or do you work with one winding at a time?
3. I hope that you are aware that "another metal (i.e copper, or nickel)" doesn't change inductivity much. It reduces the Q factor of the inductor and not the inductivity. OK, Ni may also change inductivity a bit.
4. Are you sure you work with hogh wnough frequencies so you do not just see the resistance of the winding?
5. Are you building another metal detector or proximity switch?
6. School project?

Answer to the duct tape question: If it is duct tape (and not Al tape), it shouldn't have any influence.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[VEBill]

Two inductors on one core is also called a "transformer". One can have two inductors on one core only if you use them one-at-a-time. If you use them both at the same time, then they'll act as a transformer.

Closed cores (such as toroidal or rectangular) contain the magnetic field lines mostly within the core. So they're not influenced (much) by nearby metal. Open cores (such as a rod) would have the magnetic field lines going out/in from each end; so they will interact with (for example) nearby metal.

 

[frankyengtips]

@Skogsgurra :
1 - it is a rectangular shape core.
2 - Yes, two windings active simultaneously.
3 - Okay. Those were just examples. But I see what you mean.
4 - There are some typos? So I don't know what you are asking?
5 and 6 - building a voltage control oscilator for a project (not school).
What is AI tape?

@VE1BLL
"Two inductors on one core is also called a "transformer". One can have two inductors on one core only if you use them one-at-a-time. If you use them both at the same time, then they'll act as a transformer."
-Does it matter if the windings are separated or on top of each other?

 

[VEBill]

"Does it matter if the windings are separated or on top of each other?"

Not really. If you can visuaslize where the magnetic lines are located within the core, it'll be obvious why it doesn't really make very much difference precisely where the windings are located around the core.

There may be minor variations from secondary effects.

 

[Skogsgurra]

"4 - There are some typos?" Sure, look at a keyboard and see what's close to w and o. You may be able to figure it out.

Al is aluminum. Or aluminium if you are in that part of the world.

If the two windings are active simultaneously, I hope that you are aware that only one of them can successfully be driven.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.