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margolisd

My Demagnetiser is Magnetising

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Hi all. I discovered this hairspring was magnetised. And it seems to be impossible to demagnetise. In fact, my demagnetiser seems to be making this and other metal parts worse. Does anyone know why this might be happening? It's a cheap Chinese thing. Is it time to replace it? Does anyone have any recommendations? (PS, no there is no magnetism whatsoever in the screwdriver in the picture!)

IMG_1277.thumb.jpeg.117ecb4b421b98365b8d438a848b2bb7.jpeg

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With these cheap Chinese ones you need to keep your finger on the button and draw the part slowly out of the magnetic field. I've got one too, and they don't come with instructions, but if you do that it should work OK.

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Hi   I made my own using a transformer AC  stepped down 12v output  thro a fuse and a  switch  and an old disc drive voice coil ( a former with insulated wire ) The former is just a tube . when all connected up  place the object .  Tweezers, screwdriver in the coil and power on for a few seconds whilst holding the object in the coil then withdraw the object whilst maintaining power then switch off that should do the trick.  The Chinese ones are a coil of wire wrapped round a soft iron core and act like a magnet the manner of use is same as above  The hollow coil on the home made version creates an all round field of magnetism. Google magnetic fields  on oils and bar magnets for more info

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7 hours ago, margolisd said:

It's one of these:

afaik same idea as a tunnel.  As the current alternates, pole of the magnet (created by a coil) reverses.  I don't know anyway that it could magnetize, unless there was no current going to the coil and the core had been magnetized, even at that probably grasping at straws. 

I'd take it apart and see if there's a loose/poor connection.  If current is flowing, it should work.  Have you got a meter that you can measure AC current with?

Edited by measuretwice

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I suspect that the coil must be being energized with DC rather than AC, if it is magnetizing rather than demagnetizing. However without knowing what is inside the thing it is difficult to see what might have failed to cause that problem.

If there is a circuit inside that converts mains AC to DC, to high frequency AC, which is a possibility, then if the oscillator failed, it would produce a static magnetic field, rather than the necessary alternating one.

Pop the cover off it and let us see both sides of any circuit board, and I can refine my wild speculation.

Old fashioned colour cathode ray tube degausing coils  used a slightly different and much simpler arrangement, however if they failed, then they tended to simply stop working, and either pop the line fuse, or your TV would slowly develop some weird colour artifacts as a result.


In summary, show me some pictures of the "brains" of the device.

Edited by AndyHull

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Place the component to be de-gaussed on the Chinese unit. Press the operate button, for a couple of seconds then Slowly remove the component to about one metre away. Switch unit off. Your component will now be de-magnetised. Moving the component slowly away whilst unit is switched on reduces the E&H field with distance and this slowly reduces the AC field strength by inverse square law.  Mine works very well.

Edited by ecodec

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Look at the coils of the H/S as you try to demag it. I beat they are vibrating all over the place, basically they are moving within the magnetic field lessening the demagnatising effect.

Try sitting the hairspring carefully in some rodico so it can't move as much and try again.

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6 minutes ago, Tmuir said:

Look at the coils of the H/S as you try to demag it. I beat they are vibrating all over the place, basically they are moving within the magnetic field lessening the demagnatising effect.

 

thats a good point....that would let it move with the switch poles possibly even enough to magnetize it a bit as the OP thought was happening.

as a test, magnetize a piece of steel and see if it gets demagnetized, if that works I'm thinking Tmuir has got it

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17 hours ago, Klassiker said:

With these cheap Chinese ones you need to keep your finger on the button and draw the part slowly out of the magnetic field. I've got one too, and they don't come with instructions, but if you do that it should work OK.

   the instructions are in de Carles book.

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Yeah, thanks Tmuir you are indeed correct. Preventing the HS from vibrating causes it to demagnetise. I put it in a plastic bag and held it gently in my fingers and it worked.

Does this mean it's best to remove the hairspring to demagnetise a watch movement and do the HS separately? As I'm sure it was my attempt to demagnetise a movement that ended up magnetising the HS in the first place.

Another thing that seemed to help, before I was only holding the button down and moving the object about half a meter out of the field. A full meter as suggested by ecodec actually seemed to make a big difference.

Thanks everyone. Mystery solved.

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That device is actually incredibly simple, albeit slightly crude.

The circuit appears to be as follows... Part one is mains in, through a small switch (possibly mains rated, possibly not, but given the long shafted plastic button, not something I would worry about) which energizes a good old fashioned 1980s style wall wart transformer, from the days before even the cheapest wall wart had a switch mode power supply in it. I can't see the output side of the transformer, it may have a small resistor to load it up and increase the magnetic field, or it may simply be open circuit.

The magnetic field from that does the actual degausing.

Part two consists of a high value resistor (Brown Black Yellow = 100k Ohm) and LED (across the mains, slightly dubious practice, but not that dangerous), the LED only lights when the button is pushed.

One thing I would recommend is to ensure you have a 3A or even 1A fuse in the mains plug.  From a safety perspective though, as cheap goods from China go, it looks reasonably safe. If the switch fails closed, the thing stays on (not a problem), if the switch fails open it fails to energizes and the light stays off.. also not a problem.
The only issue is that the unit has no built in fuse, so you would be relying on the plug fuse to blow if the transformer winding failed shorted, hence the comment about using a 3A or 1A fuse.

It certainly looks a lot less likely to burn the house down than a lot of badly constructed modern cheap wall warts, but I would still recommend unplugging it when not in use.

I might even get one. At round about a fiver, shipped from China, it is probably as easy and cheap to pick up one of these as it would be for me to go through my electronic scrap bin to scavenge the parts.

Edited by AndyHull

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A quick back of the envelope calculation suggests the LED is drawing about 3mA, so it wont be very bright, but by the same token the resistor is operating at a reasonably safe level, assuming it to be 1/2 Watt.

If as may well be the case, it is a 1/4 Watt, then don't hold the button too long (not more than perhaps 30 seconds max, which is all you need anyway), or the resistor will get pretty hot and if repeatedly stressed like this, eventually fail.

If the resistor fails (it would generally blow open circuit), it is no big deal,  the unit will still operate, but the light wont work.

If the resistor fails, or starts to look a little cooked over time,  swap it out for a 1W 100 k Ohm replacement.

Oh, and perhaps rather obviously, don't operate it with the back cover off, as all of that wiring and soldering is live at mains voltage.

Edited by AndyHull

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This takes me back to the times when I had the ambition to be a teacher an revolutionize the world.

As Andy already said the only way to magnetize anything with a setup like that is if it somehow was introduced with a Direct Current (DC), then it would act like an electro magnet instead. That setup  would introduce an permanent magnetic field with just one direction.
The fact it is in only one direction makes metals containing Iron, nickel or cobalt magnetic through organizing the free electrons to point in one direction. 

You might encounter the same phenomena with a alternating current (AC) but it is a slight less risk since the magnetic field is alternating periodically and with that the electric field. This makes the electrons retain an chaotic state and by that being non magnetic.

Sometimes when I get bored I use an old fashion high powered degaussing tool  for tv and computer screens and make a bulk demagnetization of 10 to 20 watches at the time.

The frequencies in cheap demagnetizers like this is dependent of the mains. In Sweden we have 50 Hz and it might be up to 60 Hz in other countries. 

This means it switches  the magnetic field 50 to 60 times per second should be enough to the most applications. More high end devices transforms the current to DC making it possible to magnetize and demagnetize with the same tool. In demagnetizing mode it uses a switch circuit to transform the DC to higher frequency AC. But common with high end and low price tools is that they have to use some kind of coil and a open end iron core to create the magnetic field. If you try to use a normal transformer with the top bridge on it will not work as well since the magnetic field is retained inside the iron core.

But if you don't have any experience with electrics I wouldn't recommend anyone to experiment with these devices.

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Does anyone know the inductance of the "coil/transformer" in these chinese things?

With a capacitor and a two pole switch you should be able to convert it to a automatic version! (but guessing the capacitor will have to be housed by itself due to its size)

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17 hours ago, RCDesign said:

Does anyone know the inductance of the "coil/transformer" in these chinese things?

With a capacitor and a two pole switch you should be able to convert it to a automatic version! (but guessing the capacitor will have to be housed by itself due to its size)

You might be better using the same method that is linked to in my post above for CRT degausing, namely a posistor.

One other idea I had for a source of free mains voltage rated coils are scrap washing machine valve solenoids.
SolenoidValve.jpeg.b2ae4540d8cc00187caeecb28ab1f76a.jpeg

This sort of thing. If you head down to your local recycling center, you will usually find dozens of scrap washing machines. Each dead machine will have up to three of these in them, and they have the distinct advantage over old wall wart transformers that they are actually designed to produce a magnetic field.

Extract the valve from the washing machine, strip away all the mechanical gubbins, leaving just the metal slug in the core and apply mains voltage to the input terminals and demagnetise to your hearts content.

Since they are designed for continuous running, there is little danger of overheating if you are a little over zealous using them, you could demagnetise your entire toolbox without them even starting to get hot. If you need a larger magnetic field, substitute an old iron or steel bolt or a length of ferrite rod for the slug.

The only warning I will give, if playing with these or any other similar coil, is don't attempt to mount them in a box with a metal clamp round the coil or any other continuous metal loop. You will effectively build yourself a very low voltage, high current transformer, (a single turn of wire round the thousands in the core) and your metal clamp will heat up dramatically and probably emit large quantities of smoke before the coil winding burns out or the line fuse pops.

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These Chinese units are horrible (I use one). The flux level is too high because they are designed to work on 120V too. Perhaps would benefit from modding in that respect. Also, the cable in no way meets EU safety standards. It's rubberised instead of plastic, and the strands are made from monkey metal instead of copper.

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27 minutes ago, rodabod said:

monkey metal

Element 666 in the periodic table. :devil: On the plus side, the cable should help keep your workshop warm. :D
Those solder joints don't exactly inspire confidence either, but as I mentioned, for intermittent use, and assuming you unplug it when you have finished, the chances of any significant mishap are fairly low.

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I guess I should put my money where my mouth is, and buy one of these mildly hazardous machines.
What are the chances that I can look on ebay without picking up at least one more basket case watch? :geek:

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I have one of the cheapo chinese ones and it works well if used correctly.  Before this i used to use my soldering gun. This is one of the larger mains operated guns with a trigger switch to heat up the soldering head.  I put the part to be demagnetised in a small plastic pot or bag and placed it near the transformer part of the soldering gun (trial and error found the best spot), switched the gun on and slowly pulled the part away to about 1 metre over 10 seconds before switching off the gun. I believe that you can also take the parts to your local store which have a demagnetiser at the till for removing security tags !!!!

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