Tesla and wireless power
in [Design]
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From: Rich Grise, Plainclothes Hippie on 12 Aug 2010 21:42 On Sun, 08 Aug 2010 17:28:54 +1000, Grant wrote: > On Sun, 08 Aug 2010 01:35:31 -0400, Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >> >>I'm not talking about Tesla _coil_ enthusiasts. They're obviously doing >>worthwhile stuff--I mean, making 20-foot sparks is at least as useful as >>blowing up anthills with dynamite, for instance. Blowing up stuff is a >>logical consequence of having testosterone, it's fun, and it's >>occasionally a life saver. >> >>It's the wireless power transmission / over unity / extracting >>continuous power from permanent magnets / loony types I'm fed up with. > > Reminds of a problem a friend posed recently, if one gets a large > strong rare earth magnet, and hangs a heavy weight from it to a > steel beam in the shed, what's doing the work of the magnet holding > up that weight? Wont the magnet 'wear' out? There's no work done, because even though there's force, there's no motion. And I was surprised that there was a thing called a "keeper" that you could stick to your horseshoe magnet - as if shorting the "magnetic circuit" actually helped maintain the field! Thanks, Rich
From: Phil Hobbs on 12 Aug 2010 21:50 Rich Grise, Plainclothes Hippie wrote: > On Sun, 08 Aug 2010 17:28:54 +1000, Grant wrote: >> On Sun, 08 Aug 2010 01:35:31 -0400, Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >>> I'm not talking about Tesla _coil_ enthusiasts. They're obviously doing >>> worthwhile stuff--I mean, making 20-foot sparks is at least as useful as >>> blowing up anthills with dynamite, for instance. Blowing up stuff is a >>> logical consequence of having testosterone, it's fun, and it's >>> occasionally a life saver. >>> >>> It's the wireless power transmission / over unity / extracting >>> continuous power from permanent magnets / loony types I'm fed up with. >> Reminds of a problem a friend posed recently, if one gets a large >> strong rare earth magnet, and hangs a heavy weight from it to a >> steel beam in the shed, what's doing the work of the magnet holding >> up that weight? Wont the magnet 'wear' out? > > There's no work done, because even though there's force, there's no motion. > > And I was surprised that there was a thing called a "keeper" that you > could stick to your horseshoe magnet - as if shorting the "magnetic > circuit" actually helped maintain the field! > > Thanks, > Rich > It does. Crappy magnets gradually decay with time, due to the motion of magnetic domain walls. The keeper reduces the magnetic field gradient at the surface of the magnet, resulting in less driving force for the domain wall motion. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
From: Tim Williams on 13 Aug 2010 09:59 "Phil Hobbs" <pcdhSpamMeSenseless(a)electrooptical.net> wrote in message news:4C64A4DD.7040505(a)electrooptical.net... >> And I was surprised that there was a thing called a "keeper" that you >> could stick to your horseshoe magnet - as if shorting the "magnetic >> circuit" actually helped maintain the field! > > It does. Crappy magnets gradually decay with time, due to the motion of > magnetic domain walls. The keeper reduces the magnetic field gradient > at the surface of the magnet, resulting in less driving force for the > domain wall motion. Or from another point of view, it keeps the magnet biased with self-magnetization. Old magnets, like alnico, had a soft B-H curve, not nearly as square as later SmCo or NdFeB magnets. Alnico has a fairly impressive Bmax of 1.2T (typical of steel alloys and comparable to NdFeB's 1.5T), but it drops off to about 0.8T at 0 A/m. This is also why alnico magnets "burn in" with use (if anyone is old enough to have used new magnets..), and are easy to demagnetize when overdriven. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Tim Wescott on 13 Aug 2010 12:27 On 08/12/2010 06:50 PM, Phil Hobbs wrote: > Rich Grise, Plainclothes Hippie wrote: >> On Sun, 08 Aug 2010 17:28:54 +1000, Grant wrote: >>> On Sun, 08 Aug 2010 01:35:31 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >>>> I'm not talking about Tesla _coil_ enthusiasts. They're obviously >>>> doing worthwhile stuff--I mean, making 20-foot sparks is at least as >>>> useful as blowing up anthills with dynamite, for instance. Blowing >>>> up stuff is a logical consequence of having testosterone, it's fun, >>>> and it's occasionally a life saver. >>>> >>>> It's the wireless power transmission / over unity / extracting >>>> continuous power from permanent magnets / loony types I'm fed up with. >>> Reminds of a problem a friend posed recently, if one gets a large >>> strong rare earth magnet, and hangs a heavy weight from it to a steel >>> beam in the shed, what's doing the work of the magnet holding up that >>> weight? Wont the magnet 'wear' out? >> >> There's no work done, because even though there's force, there's no >> motion. >> >> And I was surprised that there was a thing called a "keeper" that you >> could stick to your horseshoe magnet - as if shorting the "magnetic >> circuit" actually helped maintain the field! >> >> Thanks, >> Rich >> > > It does. Crappy magnets gradually decay with time, due to the motion of > magnetic domain walls. The keeper reduces the magnetic field gradient at > the surface of the magnet, resulting in less driving force for the > domain wall motion. I wouldn't characterize AlNiCo magnets as crappy, and they demagnetize immediately without a keeper. They're great magnets, they've just got a limited amount of magnetomotive force available to maintain their flux density -- take away their keeper (or run too much current in the motor that they're the field magnets for) and they'll demagnetize. Rare earth magnets are scary-strong, and have magnetomotive force that won't stop -- but the last time I checked an AlNiCo magnet would still beat any rare earth magnet, hands down, if the application temperature was high enough. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
From: Phil Hobbs on 13 Aug 2010 13:38 On 8/13/2010 12:27 PM, Tim Wescott wrote: > On 08/12/2010 06:50 PM, Phil Hobbs wrote: >> Rich Grise, Plainclothes Hippie wrote: >>> On Sun, 08 Aug 2010 17:28:54 +1000, Grant wrote: >>>> On Sun, 08 Aug 2010 01:35:31 -0400, Phil Hobbs >>>> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >>>>> I'm not talking about Tesla _coil_ enthusiasts. They're obviously >>>>> doing worthwhile stuff--I mean, making 20-foot sparks is at least as >>>>> useful as blowing up anthills with dynamite, for instance. Blowing >>>>> up stuff is a logical consequence of having testosterone, it's fun, >>>>> and it's occasionally a life saver. >>>>> >>>>> It's the wireless power transmission / over unity / extracting >>>>> continuous power from permanent magnets / loony types I'm fed up with. >>>> Reminds of a problem a friend posed recently, if one gets a large >>>> strong rare earth magnet, and hangs a heavy weight from it to a steel >>>> beam in the shed, what's doing the work of the magnet holding up that >>>> weight? Wont the magnet 'wear' out? >>> >>> There's no work done, because even though there's force, there's no >>> motion. >>> >>> And I was surprised that there was a thing called a "keeper" that you >>> could stick to your horseshoe magnet - as if shorting the "magnetic >>> circuit" actually helped maintain the field! >>> >>> Thanks, >>> Rich >>> >> >> It does. Crappy magnets gradually decay with time, due to the motion of >> magnetic domain walls. The keeper reduces the magnetic field gradient at >> the surface of the magnet, resulting in less driving force for the >> domain wall motion. > > I wouldn't characterize AlNiCo magnets as crappy, and they demagnetize > immediately without a keeper. They're great magnets, they've just got a > limited amount of magnetomotive force available to maintain their flux > density -- take away their keeper (or run too much current in the motor > that they're the field magnets for) and they'll demagnetize. > > Rare earth magnets are scary-strong, and have magnetomotive force that > won't stop -- but the last time I checked an AlNiCo magnet would still > beat any rare earth magnet, hands down, if the application temperature > was high enough. > I don't doubt that Alnico has its uses still, but for my money a magnet that dies when you look at it funny is a crappy magnet. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
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