How do I identify a ferrite core material. - Page 1
Forum section: electronics / rf-microwave

author: Qmavam
author_rank: Regular Contributor
timestamp: September 04, 2019, 06:03:10 pm
content: I have this ferrite E core that had a most of the center leg removed but not all.I have since remove the portion that was there.Now I want to verify the material, but don't now how to with an airgap.If I could find the AsubL I may have some reference to find the material.But with an air gap?Thanks, Mikek

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: September 06, 2019, 02:54:34 pm
content: A ham radio hangout , lots discussion about this subject ,http://forums.qrz.com/index.php?threads/identifying-toroidal-cores.168925/page-2

author: Qmavam
author_rank: Regular Contributor
timestamp: September 09, 2019, 12:09:08 am
content: Quote from: KD0CAC John on September 06, 2019, 02:54:34 pmSorry been out of town.That link give me some help, I like the idea of finding were Q=1 for the core and then comparing that frequency to permeability graphs to find what matches.Now, how do I measure a Q of 1? I have a Q meter, but anything below Q=20 is difficult.Would the phase angle be 45* when the core has a Q of 1?The fact that cores even have a Q is a new concept to me, about two weeks old.Thanks, Mikek

author: Qmavam
author_rank: Regular Contributor
timestamp: September 10, 2019, 12:26:38 am
content: [ Specified attachment is not available ]Here's what the poster on the other group said about a method to ID the material."I identify cores with a MFJ259 by winding a few turns and looking for the frequency where R=X c values. That would be where Q is 1.Then I look on a list of cores for the point where the reactance and resistance curves cross at or near the same frequency.If the Q=1 point is out of range, I look at turns and reactance and try to match a known core.I have the same impedance measuring test set most manufacturers use to evaluate core materials, but most cases the MFJ259 works good enough."Here's a permeability graph showing how the lines cross, different materials cross at different frequencies.This one crosses right at 400kHz.I have found to the best of my ability the Q=1 frequency. It is approximately 365kHz.Several materials are close to that.3C11 =375kHz Permeability =43003E25 = 395kHz u' = 60003E26 = 310kHz u' = 70003E5 = 350kHz u' = 10000I have gathered some other data, but I can't make it fit any material.The asubL is near 3500, measured with 337 turns, 387 t and 724 t, 3530, 3525, and 3470 respectively. When I measured with 100 turns I got 2900.All of those are with a gap of 0.225" Measurement frequency 100kHz.(I filled the gap with a toroid of permeability 5000 and it only increased AsubL by 7%, This surprised me. I lapped the toroid so when I put it in the E core gap, it was tight, no gap. I don't know what the (small) 7% change means?) As in this picture, although without the wire, I put the core completely inside the gap.If you have any info on how to identify my E core, please chime in.Here are the dimensions of my E core.

author: duak
author_rank: Super Contributor
timestamp: September 10, 2019, 06:33:15 pm
content: This problem is like trying to figure out what's actually in a hot dog wiener. Do you know what the core was from? A power supply or a CRT flyback transformer?100 KHz is close to the Q=1 frequency. Do the AsubL values change much when at a lower frequency, say 10 KHz, 1 KHz or even 100 Hz?The parasitic winding capacitance may have some effect.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 10, 2019, 06:53:37 pm
content: Measuring the core Q in a gapped configuration isn't very easy. The effective permeability (including the loss factor) is diluted by the air gap.It's probably easier to sample a small part of the core, or grind it down flat (in which case, it won't fit on any bobbin it was designed for, if you have any such bobbins), and measure it properly that way.In the mean time, I would assume worst case, ZnMn, Bsat >= 0.3T, Fc >= 100kHz, mu_r >= 2000, etc.Tim