I have a Toroidal inductor core (from an old circuit) (OD-25mm, ID-14mm, H-11mm, color-Gray). inductance measured for different turns are as follows (T-L)
"2 - 0.01mH
3 - 0.04mH
4 - 0.09mH
5 - 0.15mH
6 - 0.21mH
7 - 0.29mH
8 - 0.38mH
9 - 0.49mH
10 - 0.6mH
11 - 0.73mH
12 - 0.86mH
13 - 0.98mH
14 - 1.14mH
15 - 1.31mH
16 - 1.48mH
17 - 1.67mH
18 - 1.86mH
19 - 2.07mH
20 - 2.28mH "
I want to use it for an SMPS circuit
can anyone pls identify the core model, material, max flux, saturation current etc.

 

Inductance is proportional to the square of the number of turns.
Therefore the inductance for 20 turns should be four times the inductance for 10 turns.
So you can work out the permeance, but that isn't enough to know how it would be have.
If it's ferrite then you can't use it as an energy storage inductor, unless it has a gap (you would be able to see the gap under the varnish)
If you want to know if it is ferrite or iron powder cut it apart. Iron powder will cut with a hacksaw, ferrite needs a diamond saw.
It could be one of dozens of other materials:- Sendust, Molypermalloy etc. all with different characteristics.
With those inductance values, it is probably ferrite.

 

If it's ferrite then you can't use it as an energy storage inductor, unless it has a gap

Can you explain this? Are the toroids you often see on DC to DC converters not ferrite or are they gapped? I was not aware of this.

 

Can you explain this? Are the toroids you often see on DC to DC converters not ferrite or are they gapped? I was not aware of this.

Almost certainly some distributed-gap material, usually iron powder (because it’s cheaper than sendust, molypermalloy etc.)
If the cores are painted two colours, then they are Micrometals iron powder cores, you will usually see yellow-white (type 26) at 50kHz and blue-green (type 52) at 100kHz.
Ferroxcube did some gapped ferrite toroids, but they are rare.
I’ve tried to gap some myself with a diamond saw in a Dremel, but they become a real pain to wind unless you can neatly fill the gap with something.

 

Okay, but I was looking for an explanation of why ferrite ungapped does not work?

 

Okay, but I was looking for an explanation of why ferrite ungapped does not work?

A large amount of permeance and a small value of Bsat.
The gap adds reluctance, which therefore needs more magnetomotive force to produce a given amount of flux.