# Magnetics permeability **URL:** \ **Category:** PLECS\ **Tags:** magnetic\ **Created:** [March 31, 2025, 12:53pm UTC](https://forum.plexim.com/t/magnetics-permeability/1988 "2025-03-31T12:53:08Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![Florian](https://avatars.discourse-cdn.com/v4/letter/f/898d66/32.png) [@Florian](https://forum.plexim.com/u/Florian)\ **Post date:** [March 31, 2025, 12:53pm UTC](https://forum.plexim.com/t/magnetics-permeability/1988/1 "2025-03-31T12:53:08Z")
Hello, I am using the saturable core in PLECS. What exactly is meant with µ\_r,unsat and µ\_r,sat? I am using Ferrxocube cores, in the datasheet I can find values for the AL value of the specific core or the µ\_i initial permeability of the core material. How can I calculate or find the values needed for the saturable core in PLECS? Or can I use the µ\_i as µ\_r,unsat? Thank you. ---
**Author:** ![Bryan\_Lieblick](https://dub1.discourse-cdn.com/flex006/user_avatar/forum.plexim.com/bryan_lieblick/32/10_2.png) [@Bryan\_Lieblick](https://forum.plexim.com/u/Bryan_Lieblick)\ **Post date:** [April 2, 2025, 4:27pm UTC](https://forum.plexim.com/t/magnetics-permeability/1988/2 "2025-04-02T16:27:05Z")
The Saturable Core component documentation shows the how the µ\_unsat and µ\_sat relates to the BH curve. [Ferroxcube application notes](https://www.ferroxcube.com/en-global/download/download/11) define a clear difference between initial permeability μ\_i (pg. 7 eq. 4) and effective permeability μ\_e (pg. 7 eq. 5). One is a purely material property while the other takes into account gapping. The inductance factor (AL) is defined in the same document on page 9 / eq 27 and is a function of μ\_e, which takes into account gapping. So in PLECS, you can have a Saturable Core component that models the material based on μ\_i, with the gap seperately modeled, or of the core based on μ\_e which includes the gapping effects in the Saturable Core component. You should be able to define a consistent relationship between all three variables, although if they are inconsistent it could be due to fringing effects for larger air gaps that Ferroxcube might include in AL/μ\_e. ![image](https://europe1.discourse-cdn.com/flex006/uploads/plecs/original/2X/c/c248249d0002f6c9bb3afcde481cc0cbaad5f3fb.png). ---
**Author:** ![Florian](https://avatars.discourse-cdn.com/v4/letter/f/898d66/32.png) [@Florian](https://forum.plexim.com/u/Florian)\ **Post date:** [April 3, 2025, 6:54am UTC](https://forum.plexim.com/t/magnetics-permeability/1988/3 "2025-04-03T06:54:56Z")
Hello Bryan, thank you for your answer. This clarifies it. I looked at the “flyback\_converter\_with\_magnetics” [demo model](https://www.plexim.com/de/support/application-examples/186). The model description says, a Ferroxcube 2616 pot-core made of 3C91 material is used. The core dimensional parameters in PLECS are exactly like in the core datasheet, but µ\_r,unsat = 9550. When I look in the [Ferroxcube datasheet for the 3C91](https://www.ferroxcube.com/upload/media/product/file/MDS/3c91.pdf) material, I can’t find this value, only µ\_i = 3000. Where does this value 9550 come from? There is also a leakage flux path included. Can I get this value also from the datasheet? Or do I have to take real measurements to include it in the simulation? Thank you ---
**Author:** ![Bryan\_Lieblick](https://dub1.discourse-cdn.com/flex006/user_avatar/forum.plexim.com/bryan_lieblick/32/10_2.png) [@Bryan\_Lieblick](https://forum.plexim.com/u/Bryan_Lieblick)\ **Post date:** [April 3, 2025, 6:21pm UTC](https://forum.plexim.com/t/magnetics-permeability/1988/4 "2025-04-03T18:21:50Z")
> Where does this value 9550 come from? The derivation of this value is not part of the demo model documentation. However, the 3000 value of µ\_i from the 3C91 datasheet is actually at 0.25 mT and not at 0 mT as the Ferroxcube material I linked would have suggested. Looking at the 3C91 data close to 0 mT, as would be the relevant conditions in the PLECS model, the slopes are noticeably steeper and the value was closer to 10k. I would say that explains the discrepancy. > Can I get this value also from the datasheet? Or do I have to take real measurements to include it in the simulation? Leakage inductance is effected by winding techniques (i.e. interleaving) and so it isn’t something you can find on a datasheet. Measurements are ideal, although in the absence of a prototype I’ve come across a rule of thumb, that the leakage is typically 3-5% of the magnetizing inductance for a flyback transformer. ---
**Author:** ![Florian](https://avatars.discourse-cdn.com/v4/letter/f/898d66/32.png) [@Florian](https://forum.plexim.com/u/Florian)\ **Post date:** [April 3, 2025, 7:07pm UTC](https://forum.plexim.com/t/magnetics-permeability/1988/5 "2025-04-03T19:07:56Z")
> [@Bryan\_Lieblick](#): > > Looking at the 3C91 data close to 0 mT, as would be the relevant conditions in the PLECS model, the slopes are noticeably steeper and the value was closer to 10k. I would say that explains the discrepancy. What data figure in the datasheet do you mean here? ---
**Author:** ![Bryan\_Lieblick](https://dub1.discourse-cdn.com/flex006/user_avatar/forum.plexim.com/bryan_lieblick/32/10_2.png) [@Bryan\_Lieblick](https://forum.plexim.com/u/Bryan_Lieblick)\ **Post date:** [April 4, 2025, 5:50pm UTC](https://forum.plexim.com/t/magnetics-permeability/1988/6 "2025-04-04T17:50:59Z")
Fig.3 Typical B-H loops in the 3C91 material sheet. ---
**Author:** ![Florian](https://avatars.discourse-cdn.com/v4/letter/f/898d66/32.png) [@Florian](https://forum.plexim.com/u/Florian)\ **Post date:** [April 4, 2025, 8:12pm UTC](https://forum.plexim.com/t/magnetics-permeability/1988/7 "2025-04-04T20:12:41Z")
![grafik](https://europe1.discourse-cdn.com/flex006/uploads/plecs/original/2X/5/5a3b15f87d79649599dc0e569e637b1d7b4ab198.png) Hello Bryan, when looking at the graph, I can’t really see a difference between 0mT and 0.25mT. The graph reaches up to 500mT, so a 0.25mT difference is not really visible, or am I missing something? Are there any additional information/documents about this topic? I am not really sure what value for µr\_unsat I should use for my specific core. In the other demo models where the saturable core is used, the µr\_unsat is also different to datasheet values and also not documented in the model description. ---
**Author:** ![Bryan\_Lieblick](https://dub1.discourse-cdn.com/flex006/user_avatar/forum.plexim.com/bryan_lieblick/32/10_2.png) [@Bryan\_Lieblick](https://forum.plexim.com/u/Bryan_Lieblick)\ **Post date:** [April 4, 2025, 8:31pm UTC](https://forum.plexim.com/t/magnetics-permeability/1988/8 "2025-04-04T20:31:47Z")
Sorry, that was a typo in my original post - it’s 25 mT as shown in the datasheet. Fundamentally you’re trying to fit a square peg (hysteretic BH curve) into a round hole (Saturable Core component). To use the Saturable Core you need to make some engineering assumptions and pick a point on the curve or average the slopes of the BH curve. The Hysteretic core might be a better fit. The component documentation shows how the BH curve relates to the various parameters. ---
**Author:** ![Florian](https://avatars.discourse-cdn.com/v4/letter/f/898d66/32.png) [@Florian](https://forum.plexim.com/u/Florian)\ **Post date:** [April 4, 2025, 8:47pm UTC](https://forum.plexim.com/t/magnetics-permeability/1988/9 "2025-04-04T20:47:17Z")
Thank you for the explanation, I will take a look at the hysteretic core. Actually, the 0.25mT in your previous answer were right, the ferroxcube datasheet gives µi for 0.25mT. ---
**Author:** ![ATYIA](https://avatars.discourse-cdn.com/v4/letter/a/fbc32d/32.png) [@ATYIA](https://forum.plexim.com/u/ATYIA)\ **Post date:** [July 19, 2025, 8:17pm UTC](https://forum.plexim.com/t/magnetics-permeability/1988/10 "2025-07-19T20:17:31Z")
Hi, I really do not understand from where , the value of the unsaturated releative permeability is used, and also the saturated releative permeability is 1 , is it ok the unsaturated releative permeabiltiy is 9950 and the saturated releative permeability is 1 Thanks ---
**Author:** ![Kris\_Eberle](https://dub1.discourse-cdn.com/flex006/user_avatar/forum.plexim.com/kris_eberle/32/6_2.png) [@Kris\_Eberle](https://forum.plexim.com/u/Kris_Eberle)\ **Post date:** [July 21, 2025, 6:19pm UTC](https://forum.plexim.com/t/magnetics-permeability/1988/11 "2025-07-21T18:19:41Z")
The 9550 value is an approximation. Looking at the BH curves in the material datasheet, you will need to determine the slope of the curve around H=0. Since neither temperature curve actually goes through the origin with these being the hysteresis curves, you are basically needing to eyeball the midpoint and do your own rise-over-run determination. As an example, if you draw a straight line from B=0 to B=100mT, this would bring us close to H=8A/m. Then, to determine mu\_r,unsat, you need to divide this slope by mu\_0: (0.1 T / 8 A/m) / (4_pi_10^-7) = 9947, which was then rounded up to 9550. ---
**Author:** ![ATYIA](https://avatars.discourse-cdn.com/v4/letter/a/fbc32d/32.png) [@ATYIA](https://forum.plexim.com/u/ATYIA)\ **Post date:** [July 22, 2025, 2:24pm UTC](https://forum.plexim.com/t/magnetics-permeability/1988/12 "2025-07-22T14:24:49Z")
Thanks for your reply, now it is very clear, I would like to verify this thing, you have taken into account the BH curve at 100 degree Celsius. Regards, ---
**Author:** ![Kris\_Eberle](https://dub1.discourse-cdn.com/flex006/user_avatar/forum.plexim.com/kris_eberle/32/6_2.png) [@Kris\_Eberle](https://forum.plexim.com/u/Kris_Eberle)\ **Post date:** [July 22, 2025, 2:43pm UTC](https://forum.plexim.com/t/magnetics-permeability/1988/13 "2025-07-22T14:43:30Z")
That is correct. So you can feel free to adjust for temperature in your application as needed. Using the 25 C curves doesn’t result in a big difference in H using the slope around H=0 (~5 A/m), but I understand that leads to a pretty significantly different value of mu\_r,unsat. ---
**Author:** ![ATYIA](https://avatars.discourse-cdn.com/v4/letter/a/fbc32d/32.png) [@ATYIA](https://forum.plexim.com/u/ATYIA)\ **Post date:** [July 22, 2025, 2:53pm UTC](https://forum.plexim.com/t/magnetics-permeability/1988/14 "2025-07-22T14:53:43Z")
Thank you indeed, really thank you