How to Identify Ferrite materials

V

VK3YNV

Guest
Here is a video describing a fairly simple method to identify the ferrite type for an unknown core. It works by measuring the magnetic permeability and comparing with the data on the Fair-Rite web site.


The spreadsheet is here https://www.fair-rite.com/wp-content/uploads/2020/05/Toroid-and-Rod-Perm-Calc-003.xls

Might be handy if like me you have ferrite toroids of unknown origin and properties.

Edit: I have added XLS to the accepted file types, so I've attached the spreadsheet.
 

Attachments

Last edited by a moderator:
V

VK3YNV

Guest
Testing some toriods using the above method.

First up is a toroid that somehow ended up in the junk parts bin..

IMG_3681.JPG


10 turns gives me 135 uH, so entering that into the spreadsheet

OD(mm)​
ID(mm)​
HT(mm)​
C1​
C2​
le(mm)​
Ae(mm2)​
Ve(mm3)​
N​
Lo(nH)​
Ls (uH)​
µI​
Sample1​
61​
36​
12.67​
0.94035​
0.00608​
145.52​
154.75​
22520.46​
10​
133.636​
134.93​
1010​

So the initial magnetic permeability ui at 10 KHz is 1010

Looking up the material properties on the fair-rite website the closest match is type 43.

Just to check, I tested some toroids i bought from Farnell that is supposed to be type 61.

IMG_3682.JPG


So entering the numbers into the spreadsheet.

Sample2​
35.46​
22.94​
12.6​
1.14495​
0.01475​
88.89​
77.64​
6901.87​
10​
109.755​
17.02​
155​

So the initial magnetic permeability at 10 KHz is 155

The nearest type from the fair-rite website is type 61, which is what it's supposed to be. :)

The type 43 is ok for inductive applications ( like rf transformers ) up to 10 MHz, and suppression applications from 20 MHz to 200 MHz

Type 61 is ok for inductive applications up to 40 Mhz and suppression applications 200 MHz to 2000 MHz
 
V

VK3YNV

Guest
Rob kindly sent me some data on the Jaycar LO1238 Toroid, which I was curious to check, our local Jaycar has sold out.
Inductance measured At 50 KHz
OD(mm)​
ID(mm)​
HT(mm)​
C1​
C2​
le(mm)​
Ae(mm2)​
Ve(mm3)​
N​
Lo(nH)​
Ls (uH)​
µI​
34.4​
20.8​
12.56​
0.99431​
0.01189​
83.15​
83.62​
6953.99​
10​
126.383​
108​
855​

Might be a bit higher inductance if we extrapolate down to 10 KHz ( Which is where Fair-Rite specify their initial permeability data. )

So what's the result if we guess around 120 nH

OD(mm)​
ID(mm)​
HT(mm)​
C1​
C2​
le(mm)​
Ae(mm2)​
Ve(mm3)​
N​
Lo(nH)​
Ls (uH)​
µI​
34.4​
20.8​
12.56​
0.99431​
0.01189​
83.15​
83.62​
6953.99​
10​
126.383​
120​
949​

Turns out it doesn't change the conclusion as to the material type, the closest ferrite type is type 43.

So we can conclude the Jaycar LO1238 ferrites are equivalent to type 43.
 
Last edited by a moderator:
V

VK3YNV

Guest
I was in Jaycar earlier today and noticed that the LO1238 Ferrite Toroids are back in stock, so I got a packet of 2 to check the ferrite type.

OD(mm)​
ID(mm)​
HT(mm)​
C1​
C2​
le(mm)​
Ae(mm2)​
Ve(mm3)​
N​
Lo(nH)​
Ls (uH)​
µI​
34.31​
20.6​
12.52​
0.98371​
0.01171​
82.61​
83.98​
6938.97​
10​
127.744​
90.8​
711​

The closest initial permability mix is Fair-Rite Type 43.
 
B

BillC

Guest
I have a few toroids here some from old unused gear . Would it be possible to do a frequency sweep with a TG. and Analyzer to obtain an indication of loss/frequency etc. How best to couple into a toroid, we could possibly make a simple test jig with sockets and terminals ,what do you think Ray?
 
V

VK3YNV

Guest
Hi Bill,
It's a complex topic, and I don't really know if an S21 sweep would be enough to identify the ferrite material. It would of course give you a pretty good idea of how inductance changes across the frequency range caused by way permeability changes with frequency. That might provide a good clue as to the ferrite type. It would be a good project to build something and test the concept.

I think the best approach for baluns is to build it and then do the measurements under the conditions the balun is going to operate.
 
B

BillC

Guest
Thanks Ray, . When I get a chance I might build a simple test fixture with sockets and terminals ready mounted , it could come in handy for testing various devices. Cheers.
 
Top