Permanently magnetised toroid - Page 1
Forum section: electronics / projects

author: ricko_uk
author_rank: Super Contributor
timestamp: October 02, 2020, 12:36:09 am
content: Hi,I wanted to try some experiments/ideas (nothing to do with electronic circuits) with toroids.1) Are there any standard toroids made with materials that magnetise with relatively low currents and remain permanently magnetised?2) Speaking just of materials, what materials are most easily permanently magnetised with relatively low currents?Thank you

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 02, 2020, 12:45:46 am
content: Quote from: ricko_uk on October 02, 2020, 12:36:09 amThat's called "magnetic hysteresis" and is usually an undesirable property of core materials. There was, however, an application that put it to good use - core memory.

author: profdc9
author_rank: Frequent Contributor
timestamp: October 02, 2020, 01:03:48 am
content: Perhaps you can find some of the toroids that were used with magnetic core memory. They are usually teeny tiny though, as a typical core memory might be thousands or tens of thousands of cores, each core being a single bit of memory.https://en.wikipedia.org/wiki/Magnetic-core_memory

author: srb1954
author_rank: Super Contributor
timestamp: October 02, 2020, 01:35:45 am
content: Quote from: profdc9 on October 02, 2020, 01:03:48 amIn ancient times large cores with a very square hysteresis loop were manufactured for use in magnetic amplifiers. Probably the only place you would find such cores today is in a dark and dusty corner of an obscure technical museum.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 02, 2020, 01:39:19 am
content: Any ferrite will do, if you don't mind that the remenance simply isn't very much, and is a relatively small fraction of saturation.Tim

author: ricko_uk
author_rank: Super Contributor
timestamp: October 02, 2020, 02:34:15 pm
content: Thank you all

author: uer166
author_rank: Super Contributor
timestamp: October 02, 2020, 05:40:33 pm
content: Search "square BH curve" and "nanocrystalline/amorphous" magamp cores. Their remanence is basically same as the saturation value. They're used in magamps, fluxgate current sensors/compasses, and as noise suppression.Here is one with a lot of hysteresis that I designed a fluxgate with:https://www.digikey.com/en/products/detail/toshiba-semiconductor-and-storage/MS-21X14X4-5-W/4701157?s=N4IgTCBcDaICoHsDOALAlgIwIYAICyAyiALoC%2BQAThe saturation current is tiny, in the order of ~100mA-turns

author: uer166
author_rank: Super Contributor
timestamp: October 02, 2020, 05:46:53 pm
content: Quote from: srb1954 on October 02, 2020, 01:35:45 amThese cores are still manufactured in huge volumes by the likes of Hitachi, although maybe not for magamps. They;re easy to find if you know where to look, for example:https://dxtmagnetics.com/?s=metglas&post_type=product&type_aws=true

author: ricko_uk
author_rank: Super Contributor
timestamp: October 02, 2020, 10:27:44 pm
content: Thank you all!So, with reference to the attached screenshot lets consider the blue curve and lets say that it crosses the horizontal axis at roughly 80 A/m and saturates at 200 A/m. If instead of saturating the core at 200 A/m it is driven only to 100 A/m then the current is removed, does it:a) go back following/tracing the initial rising blue line so the Mag field strength goes back to 0 orb) does it go back horizontally (parallelthe top horizontal line) so that the field strength remains permanently at roughly 0.2 T?Thank you

author: uer166
author_rank: Super Contributor
timestamp: October 02, 2020, 10:34:44 pm
content: Quote from: ricko_uk on October 02, 2020, 10:27:44 pmSomewhere in-between, you would need to generate multiple BH-loops at the different excitation levels and see how it goes. See attached, in that example it would go back somewhere horizontally back to 0A/m, keeping most of of the magnetization. I think it's generally closer to your option "b".

author: julian1
author_rank: Frequent Contributor
timestamp: October 02, 2020, 10:51:37 pm
content: QuoteWhatever the hell this thing is made off. You turn it off or on with a pulse, and it stays magnetized, without more power draw.https://youtu.be/5SFnZIZa_ZI?t=870

author: David Hess
author_rank: Super Contributor
timestamp: October 03, 2020, 04:47:55 am
content: Quote from: srb1954 on October 02, 2020, 01:35:45 amThey are still common in computer power supplies that have multiple outputs. The 5 and 3.3 volt outputs may use a simple magnetic amplifier fed from the 12 volt output allowing independent regulation of all outputs.

author: jbay
author_rank: Newbie
timestamp: October 03, 2020, 05:01:30 pm
content: I recommend *not* using typical magnetic core materials, such as ferrite or silicon strel, because they've mostly been optimized for minimal hysteresis. Unless you care a lot about minimizing eddy currents too.Buy a round piece of D2 tool steel and drill a hole in it, perhaps? I've tested it and found that it has a very high hysteresis compared to most other steels.

author: MosherIV
author_rank: Super Contributor
timestamp: October 03, 2020, 05:49:56 pm
content: Yes, I was thinking about using steel washer.Problem is winding.

author: ricko_uk
author_rank: Super Contributor
timestamp: October 03, 2020, 09:04:52 pm
content: Thank you all!