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 Post subject: magnet re-magnitizer question
PostPosted: Jun Thu 20, 2019 2:13 pm 
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Was looking at an email for electronics goldmine and saw some super capacitors which got me to thinking about something.

The external flash units for cameras.

Would that be something where I could place a coil of wire in series with the flash tube which is then placed over the magnet of an antique speaker and the flash activated to create a momentary high current in the wire thusfore re-magnetizing the magnet?

I would of course leave the series resistor in the circuit (if the flash unit has one) to keep the current from exceeding what the tube is rated at.


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 Post subject: Re: magnet re-magnitizer question
PostPosted: Jun Thu 20, 2019 5:25 pm 
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It's about ampere-turns. To magnetize a piece of iron or alloy, you need huge currents....hundreds of amperes; maybe thousands depending on size and material.

Commercial magnetizers use banks of paralleled capacitors and either a thyristor (SCR) or an ignitron tube to dump the charge into a large coil. Be aware that the caps must be constructed to take high peak currents for tens of milliseconds. Caps are usually not electrolytic as electrolytics tend to dislike huge current pulses.

https://www.magsys.de/index.php/en/prod ... magnetizer

You can get some magnetic results with a small current, but the magnet may not stay magnetized for very long.

Image

Rich


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 Post subject: Re: magnet re-magnitizer question
PostPosted: Jun Thu 20, 2019 5:38 pm 
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So basically the flash circuit wouldn't produce enough current, right?


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 Post subject: Re: magnet re-magnitizer question
PostPosted: Jun Thu 20, 2019 11:38 pm 
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Right!

Rich


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 Post subject: Re: magnet re-magnitizer question
PostPosted: Jun Fri 21, 2019 12:03 am 
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I'd basically need a big capacitor charged to a few KV and some sort of device to complete the circuit.

Perhaps something like this.

https://www.youtube.com/watch?v=coW1RHU ... 1K&index=5


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 Post subject: Re: magnet re-magnitizer question
PostPosted: Jun Fri 21, 2019 1:39 am 
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Yes, if you want to destroy fruit or your fingers!

The magnetizer I worked on was run from rectified 3 phase (208 V, I think). So only about 300 VDC. Capacitor bank was huge and the switch was a mercury ignitron, such as was used in industrial spot welder controls. It was used to magnetize small magnets for magnetos in a generator field exciter.

Rich


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 Post subject: Re: magnet re-magnitizer question
PostPosted: Jun Fri 21, 2019 4:53 am 
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Cool.

I may have to look into this further when I have the time and money to devote to this.

I would mainly use it on my own antique speakers.


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 Post subject: Re: magnet re-magnitizer question
PostPosted: Jun Fri 21, 2019 3:53 pm 
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Location: Monroe, NC 28112 USA
To re-energize 20s vintage headphone and horn speaker magnets, I have an almost thumb size super magnet . I put one pole of the old magnet on the super magnet and then swing the other pole over allowing it to grasp with a sharp THWACK! I do this a half dozen times and presto, the old magnet is ready to go.

I've realized that I really need to place an iron swing arm on one face of the super magnet and allow the old magnet to strike the iron and not the other pole of the super magnet... A couple of times bits of the super magnet chipped...

Robert


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 Post subject: Re: magnet re-magnitizer question
PostPosted: Jun Fri 21, 2019 4:27 pm 
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Perhaps I should try that.


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 Post subject: Re: magnet re-magnitizer question
PostPosted: Jun Fri 21, 2019 6:18 pm 
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Your success in re-magnetizing with an NdFe magnet will depend on the "Remanence" of the original magnet material.

Quote:
Remanence or remanent magnetization or residual magnetism is the magnetization left behind in a ferromagnetic material (such as iron) after an external magnetic field is removed.[1] Colloquially, when a magnet is "magnetized" it has remanence.[2] The remanence of magnetic materials provides the magnetic memory in magnetic storage devices, and is used as a source of information on the past Earth's magnetic field in paleomagnetism.

The equivalent term residual magnetization is generally used in engineering applications. In transformers, electric motors and generators a large residual magnetization is not desirable (see also electrical steel) as it is an unwanted contamination, for example a magnetization remaining in an electromagnet after the current in the coil is turned off. Where it is unwanted, it can be removed by degaussing.

Sometimes the term retentivity is used for remanence measured in units of magnetic flux density.[3]


Rich


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 Post subject: Re: magnet re-magnitizer question
PostPosted: Jun Sat 22, 2019 2:58 am 
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Forgot to mention that a couple of old timers told me that striking the tired magnet while it was in the energizer magnetic circuit with a brass hammer would strengthen the results. YMMV

Robert


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 Post subject: Re: magnet re-magnitizer question
PostPosted: Jun Sat 22, 2019 3:35 am 
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Cool


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 Post subject: Re: magnet re-magnitizer question
PostPosted: Jul Thu 11, 2019 10:02 am 
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Location: Powell River BC Canada
I was told that speakers were made with uncharged magnets. Otherwise they would fill
magnetic crap from everywhere and be hard to assemble.

That video is not wise.


Years ago practical electricity was part of high school shop.

Long gone.

A pair of youths decided to climb an electric tower. One life altering burns, Other
burned but not so badly, Got help for the first.

At that age, they can drive and swim safely. What part of school ignores the
electric grid ?

_________________
de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject: Re: magnet re-magnitizer question
PostPosted: Jul Thu 11, 2019 11:21 am 
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I meant the video as more of a joke as I would never do that given my previous experiences with HV and coming across it even when being careful.


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