Engineering magnetics -- practical introduction to BH curve

A practical introduction to understanding magnetic devices such as transformers and motors. This video covers BH curves, reluctance, permeability, DC and AC magnetic circuits, and some applications.

CORRECTION: at 13:48, I say that permeability can be negative. This is not true. All permeabilities are positive. Diamagnetic materials have permeabilities that are lower than empty space (eg .95 relative permeability). There is another quantity which is called susceptibility, which describes the ratio between flux carried by a material, and the flux carried by the space which the material occupies. This quantity can be negative.

Please put questions in the comments, and I'll do my best to answer them!

I apologize that I didn't mention inductance. This video focuses only on the magnetic side of things. Inductance is how the electrical circuit interacts with the magnetics.

[TechIngredients]

Wow! It isn't often that I watch a video several times, but this may be the best presentation of magnetic principles I have ever seen. Thanks!

[PracticalEngineeringChannel]

This is such a good presentation of the topic. Really appreciate the effort that went into this video. I learned a lot.

[DanieleGiorgino]

You condensed an entire course in transformer design and magnetism in about an hour. Well done, really informative.

[pnt]

In less than an hour, you gave me a better understanding than a 5-week segment of my physics course 👍

[InssiAjaton]

Congratulations for a great presentation!
Although there was nothing new for me, I know I would not be able to present same things without the math.
Here comes some of my personal “magnetics past”. Before I started my studies, I read some radio/electronics books and found there formulas to building a transformer necessary for the radio or other gear. There was this funny constant, 1.2 T. That was listed as a constant for the steel laminations and was used tu determine how many turns of wire was needed, along with some dimensional items and the frequency. O.K, my studies added all the hysteresis loss issues, plus Eddy Current losses to the story. And one thing that I learned was how to actually distinguish between the two kinds. Hysteresis losses increase proportional to the frequency, but Eddy current losses increase proportional to the square of the frequency. So, you measure the losses at two or more frequencies.

I worked while studying and there I was introduced to Grain Oriented Steel that had saturation level indeed at 1.5 or even 1.7 T. But if you pushed your transformer design to those numbers, you started getting occasional trips of the breaker (or in our case blown fuses) and that with no load on the transformer. Why? That was because the inrush current brought the core into saturation depending on the exact moment of the AC voltage when the primary happened to be connected. The lower grade steel is more forgiving, as the hysteresis curve tails have a bit more slope or more rounded corner, while the grain oriented material settles on much flatter way or lower slope.

Then, ferrite cores have much lower saturation limits than even the basic steels. My rule of thumb is that low frequency ferrites might be as much as 0.3 T, while high frequency applications I should not design with any higher than 0.1 T. I hope these small notes might still be digested by at least some viewers.

[xXxserenityxXx]

Currently studying Electrical & Electronic Engineering at University so have come across a lot of different teaching styles and yours is clearly the best I've seen. Thank you for your public display of passion and ingenuity.

[waew]

Really nice practical review of a deceptively complex topic!

[nicktohzyu]

you have a few significant mistakes:

diamagnetic materials do NOT have negative permeabilities, just a lower slope than vacuum
superconducting magnets do not overcome the issue of ferromagnetic saturation, they simply have a buttload of amp-turns
brass has a permeability close to air, not zero

[p_mouse]

"It's typically taught heavy on the math and theory". Unfortunately this seem to be the case on many subjects actually. Most students and interns I get who really don't have a clue what's going on.
Excellent video!

[jonnyphenomenon]

BH CURVE!!! THATS WHAT ITS CALLED!! Oh man, you have no idea how helpful this video was for me. I fly fpv racing quad copters which use really powerful brushless DC motors with really strong neodymium magnets in them.. Years ago I was discussing with a friend about how these motors wear out over time. Specifically, this friend was asking what the effect was of running the motors at really high voltage/current. I tried to explain to him how magnets are made by putting them in really strong electrical fields, and how when we use them to create rotational forces we are putting them in a similar electrical field, which as long as we stayed under a certain limit, we would get work out of the magnets, but the closer we got to the limit, the more the magnets would lose their *charge* so to speak. I remembered a little bit about the BH curve from high school physics, but for the life of me couldn't remember what it was called.

[HellTriX]

I really appreciated this. I never could understand why nobody could just give a more layman's explanation of magnetic and I was not skilled enough on the subject to break it down for people as good as you have. It goes back years when I was first winding my first transformers, I was just looking for a little assistance on how many turns and how big my wire was just to get close to something that was functional, but instantly people are like, learn this 4th year college math and you can then try.

[DrakkarCalethiel]

50 minute long video? Exactly what I love!

[IntenseGrid]

I've been in electronics as a hobbiest for more than 30 years and even did some college courses in Electronics, and you surpassed any training I have had by a long shot in this one 50minute video! You are amazing! Keep up the good work I'm subscribing now!

[grins]

I watch this every now and again. It's a great break down of the BH curve and helps give a bit of an insight into magnetics. Thank you very much.

[MrMilarepa]

I really keep coming back to this video every couple of months whenever magnets come up in any form. It's the best resource on magnetism on the whole of the internet.

[UOttawaScotty]

Excellent video, and it's so nice to see a lot of my other favorite channels commenting on this video.

[mattperttula]

I have never commented on a YouTube video before, but I really appreciated all the work you put into this. Thanks for such a concise and practical intro, this outdid any university class I took on the subject and had was way more practical. Thanks again!

[WhileTrueCode]

The fact that you so succinctly stated that "you don't really need to be exposed to the math until you actually need it" summarizes an immense problem in traditional education and open forums alike! Couldn't agree more, good sir. You are a saint among scholars.

[placidesulfurik]

You're so great, man. I just love how straightforward, no non-sense and to the point your videos are, despite being quite long. I think I'd pick your channel as my favourite on YT if I had too.

[WoLpH]

I've been playing around with magnets for about 25 years now and I've figured out several of these things through trial and error... seeing the reasoning and math behind it is amazing. Thank you so much for the fantastic explanation!