Author Topic: Electrical Demagnetizer  (Read 37003 times)

Offline John Stevenson

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Re: Electrical Demagnetizer
« Reply #25 on: March 21, 2010, 08:21:54 PM »

Surely Master Bodger Extrordinaire ?      M.B.E.  ....

Bend of knee, tug of forelock etc ?

Dave BC

I already have the MBE, stands for Motor Bike Engineer  :lol:

John S.
John Stevenson

Offline Bluechip

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Re: Electrical Demagnetizer
« Reply #26 on: March 21, 2010, 08:26:32 PM »
JS


MBE2 ?

Dave BC




I have a few modest talents. Knowing what I'm doing isn't one of them.

Offline John Stevenson

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Re: Electrical Demagnetizer
« Reply #27 on: March 21, 2010, 08:41:53 PM »
JS


MBE2 ?

Dave BC






Brilliant I like that.   :smart:

John S
John Stevenson

Offline websterz

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Re: Electrical Demagnetizer
« Reply #28 on: March 21, 2010, 09:18:22 PM »
...  (it's been quite a while since I looked at a micro tranny)...

In THAT case Darren...I have a little gift for you.



 :bugeye: :lol: :doh:
"In the 60's, people took acid to make the world weird.  Now the world is weird and people take Prozac to make it normal."
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Offline Darren

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Re: Electrical Demagnetizer
« Reply #29 on: March 22, 2010, 04:15:06 AM »
You have to wonder what some people get up to in their spare time, now I know .....















Utube .....  :lol:
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

Offline websterz

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Re: Electrical Demagnetizer
« Reply #30 on: March 22, 2010, 04:19:08 AM »
You'd be surprised at how difficult a micro tranny is to actually FIND these days! I spent a half hour looking for that little gift for ya'.  :lol:
"In the 60's, people took acid to make the world weird.  Now the world is weird and people take Prozac to make it normal."
 :med:

Offline ScroungerLee

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Re: Electrical Demagnetizer
« Reply #31 on: March 22, 2010, 11:16:20 AM »
Bernd,  any idea how many ohms that coil measures?

Thankee

Lee

Offline Bernd

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Re: Electrical Demagnetizer
« Reply #32 on: March 22, 2010, 02:45:56 PM »
Bernd,  any idea how many ohms that coil measures?

Thankee

Lee


Yup, 62.7 ohms

Bernd
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Offline John Hill

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Re: Electrical Demagnetizer
« Reply #33 on: March 22, 2010, 04:09:00 PM »
I have a bulk tape eraser from the time when we used 1" wide magnetic tapes.  As far as I can see the eraser is a single coil wound around a 'E' shaped stack of laminations.  I know the core of a transformer is usually made of laminations of shapes 'E' and 'I' stacked alternately so if you can get one apart you could reassemble with just the 'E's.

If you have a stable load, like a coil, which does not have enough resistance/reactance to limit current flow you could use a resistor (or a light bulb) to limit the current flow  but you can also use a mains rated capacitor in series, the smaller the capacitor the lower the current.
From the den of The Artful Bodger

Offline madjackghengis

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Re: Electrical Demagnetizer
« Reply #34 on: March 25, 2010, 10:08:55 AM »
Hi ya'all, I just wanted to say there is an even easier, and safer way, which is probably also cheaper, which is to take any of the kind of small ac motors, such as a phonograph motor or small fan motor, which has a shunted "stator", which you will see as a thick copper wire wrapped around the stator in a couple of places, remove the bearings and the rotor, and cut a slot wide enough for the biggest thing you want to demagnetize, either put a switch in the circuit, or unplug it to turn it off.  To use, plug it in, take what is magnetized, and put it between the two poles you left, and slowly draw it away from the motor stator until it is a couple feet away, and then turn it off or unplug it.  If you do exactly the same thing, but unplug or turn off the stator while the piece of steel is between the poles, you will very effectively magnetize it most of the time, unless by luck you switch it off while the coil was in a null of the a/c wave.  I worry about microwave transformers, because if you don't do something with the small wire side, which is the high voltage side, it can easily reach above a thousand volts on "flyback", as it is made to drive a magnetron to make microwaves, like radar.  They are great for making the primary power supply for a really powerful Tesla Coil if that is what you're into though.  My demagatizer has a stator that's about an inch and a quarter thick, and will demagnetize a six or eight pound chunk of steel easily, and I haven't bothered to be safe, I just plug it in, and un-plug it.  Opening up where the rotor goes, and leaving two poles which are a fair distance apart makes the shunted motors very efficient for magnetizing and demagnetizing, and they need no current control, which is what the light bulb effectively does.  Mad Jack

shaded pole fan motor with cord

another view, showing the hack saw cuts, to provide good poles.
« Last Edit: March 31, 2010, 08:33:48 AM by madjackghengis »

Offline wheeltapper

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Re: Electrical Demagnetizer
« Reply #35 on: March 25, 2010, 11:06:56 AM »
Hi all
Iread this thread 2 days ago and thought "what a good idea".
yesterday my neighbour said to me " my microwave oven just packed up, would you like it for the bits inside "

"not arf" says me :D

so here's my version,

inside


and outside


the box cost a couple of quid in B&Q
the rest was lying around, as it does :lol:

the coil is held down with cable ties. works a treat.

cheers
Roy
I used to be confused, now I just don't know.

Offline Bernd

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Re: Electrical Demagnetizer
« Reply #36 on: March 25, 2010, 12:15:28 PM »
Hey nice Roy.

Ah Mad Jack I've got to give one of these  :wack:

Go back and look at my OP. Notice that I use the coil with the finer wire, not the whole transformer. I remove the secondary coil and use it be itself. I was just showing what that transformer looks like when removed from the micro wave oven.

Remember the magnets in the magnetron are also good items to save.

Bernd
Route of the Black Diamonds

Offline wheeltapper

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Re: Electrical Demagnetizer
« Reply #37 on: March 25, 2010, 12:20:21 PM »
Yea, I got the magnets out as well.
thinking about it, I make something to DEmagnetise things then save 2 ruddy great magnets.
I must be mad.

incidently, if you have a mechanical wristwatch, TAKE IT OFF before switching this gadget on!!

cheers
Roy
I used to be confused, now I just don't know.

Offline madjackghengis

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Re: Electrical Demagnetizer
« Reply #38 on: March 31, 2010, 08:42:13 AM »
Ah Bernd, using just the secondary means you get to use the transformer without a core, and with enough impedence as to prevent buring up the coil.  I save those microwave transformers in case I need to hurt someone someday, you can never be too paranoid, and they are out to get you!!  Properly used, that transformer, the magnetron, and some artful wiring to an inverter and you've got a radar gun disruptor and probably disrupting all sorts of microwave communications, and maybe even wireless computers.  Might be valuable to keep around.  Mad Jack  P.S. I think I got my fan motor with the "shaded poles" off the same microwave, don't throw anything away, that's my motto!  Be Prepared!

Offline Bernd

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Re: Electrical Demagnetizer
« Reply #39 on: March 31, 2010, 08:53:07 AM »
Hey Mad Jack. Sounds like my kind of thinking on the transformer. That would be an interesting project.   :dremel:

Bernd
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Offline madjackghengis

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Re: Electrical Demagnetizer
« Reply #40 on: April 05, 2010, 09:48:43 AM »
Hey nice Roy.

Ah Mad Jack I've got to give one of these  :wack:

Go back and look at my OP. Notice that I use the coil with the finer wire, not the whole transformer. I remove the secondary coil and use it be itself. I was just showing what that transformer looks like when removed from the micro wave oven.

Remember the magnets in the magnetron are also good items to save.

Bernd
Ah Bernd, I was speaking of "flyback", which can and does occur in a single coil, in the right (or wrong) circumstances.  With that great big coil of fine wire, opening contact suddenly can give an induced high voltage pulse just as an ignition coil does, even without a second coil just from the collapsing magnetic field.  The addition of field pieces with a gap between them also improves the efficiency of the magnet as well.  If I remember right, the fan motor I used in the picture, came out of a microwave oven.  I save that high voltage transformer for the day I have to power the magnetron with it, to interfere with official radio communications and stave off the invasion of the aliens.  Mad Jack

Offline madjackghengis

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Re: Electrical Demagnetizer
« Reply #41 on: April 05, 2010, 10:05:47 AM »
Hey Mad Jack. Sounds like my kind of thinking on the transformer. That would be an interesting project.   :dremel:

Bernd
Bernd, there is a capacitor of high voltage across the magnetron, which is half a tuned tank circuit, with the transformer and the inductive load of the magnetron being the other half of the tank circuit.  Connecting it all up as it was in the original, with a spark gap installed in this high voltage circuit with the gap adjustable with a wooden handle of some sort, and getting it adjusted to where it crackles rather continuously, gives a high output of RF, and very odd and changing high frequencies, that is RF wise, about as noisy as it can get.  You do need a disc reflector of some sort on the "nozzle" output of the magnetron, to provide a "ground plane", which closes the high frequency circuit allowing the nice crackling effect.  The out put of the transformer can be run through the primary of a good high voltage car coil, and its output run into a nice dome or the like, again with an adjustable spark gap, to generate the oscillation, and you have a medium sized Tesla coil which ought to approach half a million volts or so.  Running the output of the transformer into a conventional shallow cone primary coil, with a 100 to one "tower coil" as is standard for Tesla coils will get a really good effect, and probably close on to a million volts, again with an adjustable gap.  That's just for people who really enjoy playing with high voltage and aren't afraid to die.  Working around radar too long can give a person a bad attitude toward high voltage, and a lack of proper respect.  Mad Jack

Offline Bernd

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Re: Electrical Demagnetizer
« Reply #42 on: April 05, 2010, 06:53:43 PM »
Yup, understand about the fly coil. But you got me beat on all the other info.

Guess I won't try for the high voltage, bad heart ya know.  :lol:

Thanks for explaining though. Didn't know you have such an extensive background in "electricity".

Bernd
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Offline madjackghengis

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Re: Electrical Demagnetizer
« Reply #43 on: April 09, 2010, 11:36:07 AM »
I regularly make small batches (50 or so) parts out of 4140. After hardening and surface grinding them there is always some residual magnetism in them. I bought a 4x6 surface demag'er from Enco planning to spread the parts out on a thin piece of card stock and treating a whole batch at a time. Plus it will be big enough to do drills, hand tools, etc. Just under $40 with free shipping. Cheaper than scrapping my microwave I guess... :dremel:

Being close to a transfer station (junk drop off) I've picked up the dead micro-waves. I've got at least a dozen or so transformers.

The reason I started collecting these was/is I found an article on the net about making your own spot welder using two rewound transformers. I've got the article stored some were on my disk drives.

I'm sure you could find them laying out on the curbside on pickup day.

Bernd
Hi Bernd, I have to say it felt good to catch you off guard with the fifty one hole index plate!  I was wondering if you ever did anything with the idea of the spot welder, or have any other experience with a spot welder.  I've got a top of the line ESAB welding power supply I use mostly for tig but occasionally for stick and have been considered using it, as it is all solid state, with a solid state contactor setup.  I haven't tried it yet because I seldom need to spot weld, and usually plug weld instead, so far, however if I had a good, solid set up, I would spot weld pretty often if it were convenient.  By the way, I assume your avatar is a scale model, do you have a build log or some more pictures showing more of the truck?  mad jack, out in the noonday sun, again!

Offline Bernd

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Re: Electrical Demagnetizer
« Reply #44 on: April 10, 2010, 09:45:49 AM »
Mad Jack,

I used to to do quality control on first parts coming off cnc machines. One job was checking holes on a bolt circle. So I had to figure out the  X & Y settings for the coordinate checking machine. That''s when the light came on when you said "coordinate" and the drilling the holes. Ya! I can do that.

I haven't done a thing on building the spot welder. Really no need for it. But if you interested I'll see if I can find it.

The sotry behind the avatar. That picture came out of the August 1975 Hot Rod magazine. Back then I was quite interested in cars. That truck is a total scratchbuilt vehicle. I just like the design on the old Mack trucks. Here's a pic with the full story. The guy has a web site. Google "low buck tool" and read about the way he got started.



Bernd
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