Magnets on the work bench
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From: Tim Williams on 11 Feb 2010 11:00 "Chris" <christofire(a)talktalk.net> wrote in message news:9f794283-f986-4e41-93af-5600bd2dbe34(a)z26g2000yqm.googlegroups.com... > Those are all about 1 tesla according to their table at > http://www.supermagnete.nl/eng/data_table.php, which seems typical for > Neodymium (-Iron-Boron) magnets, and those are 'the strongest magnets > in the world' according to that web site! > > Tesla is the unit of flux density. The number around 40 is an 'energy > product' apparently: the square of B, in Tesla, divided by mu0 for > air, although the unit MegaGaussOersted must involve a strange > conversion. The type 50M shows a particularly high remenance of 1.40-1.46T, from a magnetization of 860-995kA/m (which means, for a 1 cm thick magnet in a steel fixture, you need to pulse about 10kAt around it -- 100A * 100 turns let's say!). Assuming the B-H curve is exactly that square, the "energy product" is: 1.4527M T*A/m = Wb*A/m^3 = V*s*A/m^3 = J/m^3. (Webers are volt-seconds, the amount of flux applied. Volts get into it because integrating EMF over time gives flux, hence, V*s. Flux actually has nothing to do with amps, which sounds funny for magnetism which is all about amps, but it's like how current and voltage are dependent on resistance, there's a connection, it's just not a direct connection.) > I wonder if it's significant that I ordered an even number?! Perhaps > if you order three, they send you a fourth one free of charge! But then you'd have to magnetize it yourself! <rimshot> Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Tim Williams on 11 Feb 2010 11:02 "Spehro Pefhany" <speffSNIP(a)interlogDOTyou.knowwhat> wrote in message news:lh58n5tms6k40duke11c1o2n4fl9neevpo(a)4ax.com... > The 400-series (ferritic) stainlesses are quite ferromagnetic- you can > pick up big chunks with an electromagnet. 300 series stainlesses (304 and 316 are the most common) are slightly magnetic, more so when work hardened. A flat panel of 316 might not be particularly magnetic, but a sharp bend in the same sheet may be sticky enough to hold a light magnet. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Jan Panteltje on 11 Feb 2010 11:35 On a sunny day (Thu, 11 Feb 2010 09:50:45 -0600) it happened "Tim Williams" <tmoranwms(a)charter.net> wrote in <hl190l$8ft$1(a)news.eternal-september.org>: >"Spehro Pefhany" <speffSNIP(a)interlogDOTyou.knowwhat> wrote in message >news:jl58n5ldh993a68e3hb7jr83usr874a5be(a)4ax.com... >> If you feel like experimenting, it would be interesting to see if a >> BFM (big fat magnet) would kill an energized SMPS wall wart. > >Hmm, depending on orientation, it might enhance efficiency. > >Tim Core saturation would _enhance_ efficiency?
From: Dirk Bruere at NeoPax on 11 Feb 2010 11:36 Tim Williams wrote: > "Chris" <christofire(a)talktalk.net> wrote in message > news:9f794283-f986-4e41-93af-5600bd2dbe34(a)z26g2000yqm.googlegroups.com... >> Those are all about 1 tesla according to their table at >> http://www.supermagnete.nl/eng/data_table.php, which seems typical for >> Neodymium (-Iron-Boron) magnets, and those are 'the strongest magnets >> in the world' according to that web site! >> >> Tesla is the unit of flux density. The number around 40 is an 'energy >> product' apparently: the square of B, in Tesla, divided by mu0 for >> air, although the unit MegaGaussOersted must involve a strange >> conversion. > > The type 50M shows a particularly high remenance of 1.40-1.46T, from a > magnetization of 860-995kA/m (which means, for a 1 cm thick magnet in a > steel fixture, you need to pulse about 10kAt around it -- 100A * 100 turns > let's say!). > > Assuming the B-H curve is exactly that square, the "energy product" is: > 1.4527M T*A/m = Wb*A/m^3 = V*s*A/m^3 = J/m^3. > > (Webers are volt-seconds, the amount of flux applied. Volts get into it > because integrating EMF over time gives flux, hence, V*s. Flux actually has > nothing to do with amps, which sounds funny for magnetism which is all about > amps, but it's like how current and voltage are dependent on resistance, > there's a connection, it's just not a direct connection.) > >> I wonder if it's significant that I ordered an even number?! Perhaps >> if you order three, they send you a fourth one free of charge! > > But then you'd have to magnetize it yourself! <rimshot> > > Tim > I've known people stick floppy discs to filing cabinets with magnets. No harm done apparently -- Dirk http://www.transcendence.me.uk/ - Transcendence UK http://www.theconsensus.org/ - A UK political party http://www.blogtalkradio.com/onetribe - Occult Talk Show
From: Jan Panteltje on 11 Feb 2010 11:49
On a sunny day (Thu, 11 Feb 2010 21:20:24 +0800) it happened "Royston Vasey" <royston(a)vasey.com> wrote in <rtSdnVRqufGHmenWnZ2dnUVZ_oSdnZ2d(a)westnet.com.au>: > >"Jan Panteltje" <pNaonStpealmtje(a)yahoo.com> wrote in message >news:hl0uf3$u1m$1(a)news.albasani.net... >> On a sunny day (Thu, 11 Feb 2010 06:45:06 -0500) it happened legg >> <legg(a)nospam.magma.ca> wrote in >> <gcr7n51ah8qfbeugdfhsviqggptlkukt9q(a)4ax.com>: >> >>>On Wed, 10 Feb 2010 20:09:08 GMT, Jan Panteltje >>><pNaonStpealmtje(a)yahoo.com> wrote: >>> >>>>Just got myself some small magnets, these are not very strong, >>>>specified as about 1.2 Tesla IIRC, but anyways, >>>>had to take some stuff apart, and had them on the work bench. >>>>Normally screws are all over the place, but with these magnets everything >>>>just jumped to it :-) >>>>Very easy, also used the magnets to magnetise my screwdrivers... >>>>Works much easier. >>> >>>Magnetized tools can make manual smd placement a nightmare. >>> >>>RL >> > > >> I just tried the magnets on some 5.6 and 10 pF SMD caps, and they do not >> stick? > > > >I had some cheap s/steel tweezers, they got magnetised and would pull 805 >resistors around. I just tried a strip of SMD zeners, those are attracted indeed! |