Magnet zapper

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Intimidator#3
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Magnet zapper

Post by Intimidator#3 » Sat Mar 26, 2005 7:48 am

Hi

Im new to the board, a fellow slotcar racer told me about this place :)
<p> Ok so what I want to do is build a magnet zapper for remagnatizing magnets ceramic an polymer bond mags can anyone help??<p> Also i want to build a guass meter for matching magnets, I found this page http://my.execpc.com/~rhoadley/magmeter.htm an this http://my.execpc.com/~rhoadley/magmetr1.htm an one more http://my.execpc.com/~rhoadley/magmetr2.htm
But what I need is to make sure this is as accurate as possable, speed depends on it :) <p>Thanks
Kevin

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dacflyer
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Re: Magnet zapper

Post by dacflyer » Sat Mar 26, 2005 7:59 pm

i have found that heat destroys maganets of the ceramic or the types found in hard drives
(ceramic? or rare earth) i have not been able to reenergise any of them..something about heat kills them..<p>i have put some extreme heat to a few, when tinkering with in the shop,, and they just fell off the metal i was working with.. that sucked !

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Chris Smith
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Re: Magnet zapper

Post by Chris Smith » Sat Mar 26, 2005 11:25 pm

De gausers can be found at Music stores

rshayes
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Re: Magnet zapper

Post by rshayes » Sat Mar 26, 2005 11:27 pm

Permanent magnet materials have a characteristic known as the Curie Point. This is the temperature at which the magnet becomes depolarized (ie, heating the material above the Curie Temperature destroys the molecular alignment which maintains the magnetic field). Samarium Cobalt has a reasonably high Curie Temperature, that for Neodynium-Iron-Boron is considerably lower.<p>Remagnitizing these materials should be possible, but may be difficult. The coercive force required may be quite high, since the magnetic path will have a sizable air gap where the material to be magnetized is located. Usually, the rest of the magnetic path is iron or some other material with high permeability.<p>The magnetizing process is fairly fast, and pulses can be used to allow higher forces to be generated without requiring special cooling methods. Expect to deliver hundreds of amps for fractions of a millisecond. A capacitive discharge system using SCRs wiuld probably be adequate for this.<p>You might try looking for application notes on the web sites of the manufacturers of the magnetic materials.

terri
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Re: Magnet zapper

Post by terri » Sun Mar 27, 2005 5:17 am

Not sure if this is helpful, not knowing the size, etc of the magnets involved, but I used to re-magnetize old loudspeaker alnicos by clamping them in a vise, wrapping a few turns of battery booster cable around the magnet while it was in the vise, and connecting the ends to a car battery for a fraction of a second.<p>If the magnet was too small to get cable around it, I'd wrap the cable around the "arm" and movable jaw of the vise. Didn't have to be a neat winding. Just a few turns.<p>The vise formed a complete magnetic path around the magnet.<p>Sparky and dramatic, and wear gloves and glasses, and keep away from fuels, but it worked.<p>It was handy to have a couple of magnets like this around the shop, but they lost their strength if they got warm (even below the Curie point), were dropped or banged on, or were just left lying around without a "keeper."<p>I never measured whether the remagnetization resulted in "factory-strength" magnetism in the alnicos, but, as I say, it worked well enough for my purposes.<p>Perhaps an adaptation of this method might be used for the slot car magnets. Perhaps.<p>[ March 27, 2005: Message edited by: terri ]</p>
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Intimidator#3
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Re: Magnet zapper

Post by Intimidator#3 » Sun Mar 27, 2005 7:58 am

The mags are kinda small, ½x½x¼ or close and ¼x¼ I know they can be remagnatized, commercial units are out there but expensive, what I do know is alot of current or volts are stored in large caps untill full then a button connected to a relay releases this power into a metal slug of some sort<p> Anouther question on the gauss meter as well http://www.allegromicro.com/sf/1321/index.asp carries aLOT of different Hall effect sensors, which would be best for this circuit http://my.execpc.com/~rhoadley/magmetr1.htm? I wanna order some samples :)
Thanks
Kevin<p>[ March 27, 2005: Message edited by: Intimidator#3 ]</p>

terri
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Re: Magnet zapper

Post by terri » Sun Mar 27, 2005 9:03 am

JUST FOR A START TO STIMULATE FURTHER DISCUSSION FROM POSTERS SMARTER THAN I:<p>I didn't know anything about slot cars until I did a search. There doesn't seem to be anything specific on how to build a remagnetizer, but this link was a little helpful, although it related to model train motors:<p>http://members.aol.com/dgosha/mtmotors.html<p>And from this link:<p>http://www.slotside.com/tt/techman/boft5.html<p> I read: " If you're REALLY ambitious, you could even try a magnetizer..." <p>This article went on about re-magnetizing the slot car motor magnets at an angle to increase speed. This "angling" technique was not recommended.<p>Here would be the parameters for a motor magnet remagnetizer:<p>1. To remagnetize, it is important to have a complete magnetic circuit around the motor magnet. This means that the pole pieces of the remagnetizer should fit the curvature of the motor magnet as exactly as possible, and the metal (preferably soft iron or silicon steel or at least mild steel) of the remagnetizer should go all the way around from one pole of the motor magnet to the other pole of the motor magnet with no gaps. It is possible to make a magnetizer that will re-magnetize the magnets while they are in the motor frame, but I won't go into that here. This part can be hinged (with hefty iron hinges) to make insertion of the motor magnet easy.<p>2. There should be a hefty coil (let's say five turns of 10- or 12-gauge insulated wire) wrapped around the steel of the re-magnetizer, so that it looks like one coil of a transformer.<p>3. The current you are going to send through this coil should be in such a direction as to re-magnetize the motor magnet in the same direction that it was originally. Otherwise the motor will run backwards or not at all. (Search for "right-hand-rule.")<p>4. A substantial pulse of DC current should then be sent through this coil. If this pulse comes from a capacitor, I'll bet there's a hefty diode in the circuit to make the current flow in only one direction. Otherwise, the current might oscillate because of the resonance between the coil and the capacitor, resulting in no re-magnetization at all.<p>5. If a capacitor is used, about 200-500 uF of greater than 25 volts rating, charged to about 12 volts with a car battery would be about right.... I think... this is just an educated guess, just like the "five turns" of wire mentioned above is only an educated guess.<p>6. If this pulse is applied from a hefty DC current source (like a car battery), it should be applied for only a second or two. The coil on the remagnetizer assembly might get hot. Use glasses and gloves and don't do it near any inflammable items or where there are inflammable fumes around. (No diode would be required if this method is used to pulse the coil.)<p>That's the best I can do without uploading drawings, and with my limited understanding of how slot car motor magnets are re-magnetized. <p>Whenever I am doing anything "dramatic" for the first time, I keep a fire extinguisher handy until I know things won't go too far awry. And I wear a face shield and gloves. That's how come I'm still so pretty and still have ten fingers on each soft white lovely hand.<p>SAFETY FIRST! <p>(Incidentally, you can erase previous "Edited by" lines when you re-edit a post. I sometimes edit my posts five or six times.)<p>[ March 27, 2005: Message edited by: terri ]</p>
terri wd0edw

perfectbite
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Re: Magnet zapper

Post by perfectbite » Mon Mar 28, 2005 1:29 am

Terri.<p>"That's how come I'm still so pretty and still have ten fingers on each soft white lovely hand."<p>Ten fingers on each hand????? Dem maganets ain't doing you no good at all babe.<p>[ March 29, 2005: Message edited by: perfectbite ]</p>

terri
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Re: Magnet zapper

Post by terri » Tue Mar 29, 2005 4:32 pm

I meant on each foot. Thanks for pointing out the erir.<p>(Started out as just "ten fingers," then added the "on each soft lovely white hand" and forgot to change it.)<p>Duh.<p>Not babe. Dude.<p>No offence. I get that a lot.<p>[ March 31, 2005: Message edited by: terri ]</p>
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Intimidator#3
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Re: Magnet zapper

Post by Intimidator#3 » Thu Apr 07, 2005 6:40 am

I found these pics, still trying to figure this completely out, again thanks for the help http://home.comcast.net/~tempest2000/pics.htm
http://www.team1rc.com/shop/static/magnet_zappers.asp<p>[ April 07, 2005: Message edited by: Intimidator#3 ]</p>

rshayes
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Re: Magnet zapper

Post by rshayes » Fri Apr 08, 2005 9:54 pm

The pictures show the tip of the iceberg. In the second picture, the two bars on top are shown bolted to the ends of two vertical round bars. The other ends of the two round bars are probably connected by a single square bar similar to the two bars on top.<p>These bars form a magnetic circuit with a single gap as shown in the picture. The other joints should have as little gap as possible. Somewhere behind the panel is a coil of heavy wire wound around part of the magnetic circuit. This could be either around the bar connecting the two posts or around one or both of the posts. Winding the wire on the round posts might be easier and give a more compact assembly. If two coils are used, they will have to be connected such that they both try to create the same polarity of magnetization. They would probably be connected in series.<p>Air gaps in the magnetic circuit make it harder to establish the coercive force necessary to charge the magnet. The gap where the magnet material is located is necessary. Notice that in one picture, the armature has been replaced by a round rod. This means that the only large air gaps are thoes occupied by the magnet material, otherwise there is a continuous iron path. That rod probably reduces the current needed to magnetize the magnets by a factor of four or five.<p>The magnetic circuit should be iron or soft steel. Some steels tend to act as permanent magnets themselves. Some stainless steels are non-magnetic to a great degree and would not work well.<p>From the pictures, it is impossible to tell if the magnetizing current is from a discharging capacitor bank or a high current DC supply. Either one could be used.

dyarker
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Re: Magnet zapper

Post by dyarker » Sat Apr 09, 2005 8:09 am

I'm dredging up a very old memory, but something to check out -<p>To magnetize or remagnetize, heat the "magnet-to-be" above the Curie point, turn-on current to electro-magnet, cool to below Curie point, turn-off current to electro-magnet.<p>The magnetic domains in the magnet "remember" the applied magnetic field better when changing from above Curie point to below. A smaller electro-magnet is needed than with the brute force cool method.<p>Again, this is an old memory, check.<p>Cheers,
Dale Y

rshayes
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Re: Magnet zapper

Post by rshayes » Sat Apr 09, 2005 3:55 pm

That is a valid way of magnetizing a permanent magnet. I think that I have seen references to that method being known several hundred years ago using the earth's magnetic field. I have also heard of it being used to transfer patterns from iron oxide magnetic tape to chrome dioxide tape.<p>The heating and cooling should probably be slow to avoid cracking the magnetic material with the thermal shock. It will also take time to cool the interior and guarentee that it it also magnetized.<p>The real fly in the ointment may be the temperature involved. If the magnets are samarium cobalt, the curie temperature may be between 700 and 800 degrees centigrade (1292 to 1472 degrees farenheit). Other materials, such as ferrite, alnico and neodymium-iron-boron (NIB) are probably lower, but may still be high enough to be awkward. NIB has curie temperatures from 310 to 370 degrees centigrade (590 to 698 degrees farenheit). There is some information on the Arnold Magnetic Technologies web site (www.arnoldmagnetics.com).

rshayes
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Re: Magnet zapper

Post by rshayes » Sat Apr 09, 2005 4:26 pm

The Arnold site also suggests magnetizing forces between 240 KA/m and 560 KA/m. (KiloAmperes per Meter) for magnetizing Alnico. Similar values may be necessary for the other materials.<p>As a rough guess, the iron path in the magnetizers is under .4 meters (about 16 inches). The permeability of the iron is probably above 1000, so the iron part of the path is effectively equivalent to less than .4 mm. We can assume that the iron and its joints represent a path of about 1 mm.<p>With the iron slug replacing the armature, there are two air gaps in the magnetic circuit. An eyeball estimate puts these at about 4 mm each. Consider the total path to be equivalent to 1 cm in air.<p>This makes the required current less than 5600 amperes. This is actually ampere-turns, since turns are unitless. The coil could thus be 100 turns carrying 56 amps or 1000 turns carrying 5.6 amps, or any other similar combination. The current can be an impulse from a discharging capacitor bank or a DC current.<p>Remember that this is an inductor that will be loaded with a substantial amount of energy. Provide some form of suppression for the inductive kick, such as a high current diode or some other transient suppression network.<p>A DC supply controlled with a variac might be the easiest way to avoid spectacular results. Ramp the voltage up until the desired currrent flows, then ramp it back down before opening the circuit. The coil will probably get hot after several seconds at maximum current, so don't go out for a cup of coffee.<p>[ April 09, 2005: Message edited by: stephen ]</p>

dyarker
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Re: Magnet zapper

Post by dyarker » Sat Apr 09, 2005 9:59 pm

Then it is not the slot car motors running hot that is demagnetizing the motor magnets, must be vibration. Or - Are the magnets really getting weaker during racing, or is "zapping" for better perfomance a modern myth?<p>Those kind of temperatures are high for most hobbyists.<p>[ April 09, 2005: Message edited by: Dale Y ]</p>
Dale Y

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