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Thread: What is the best method to fully magnetize alnico bar magnets?

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    What is the best method to fully magnetize alnico bar magnets?

    So far I have just been buying pre-magnetized magnets but I would like to assure that some are fully magnetized. Other I may want to degauss some. What are the best methods for charging and degaussing alnico bar magnets?

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    Bent Member Chuck H's Avatar
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    Since you just got here I guess it's understandable that you open with a question. I'm not a pickup maker. I hang out on the amplifier side of this forum. But I've been here long enough to have seen these guys on the pickup forum cover this topic over and over. You need to do a forum search. There are a lot of threads that have already covered this. Different builders have different methods and solutions so you can pick the one that works or sounds best to you.

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    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

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    But can’t you just easily charge Alnico magnets by using Neodymium magnets? Lots of videos on YouTube demonstrate how easy and inexpensive to charge or discharge Alnico magnet pickups.

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    ToneOholic! big_teee's Avatar
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    The OP asked the question, the best way to fully charge Alnico bars?
    The members gave the best answer for that. A commercial charger.
    You can charge with NEOs, but bars are tricky to get evenly charged along the entire edge, with NEOs.
    T

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    Last edited by big_teee; 01-02-2020 at 05:44 PM.


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    A few years back I read here of a DIY charger that interested me. Similar to commercial units, it used a bank of capacitors discharging into a large coil. I have a pair of very powerful, large neos that I'd intended to use to charge pickups but I've yet to work out how to use them effectively. The trick is to get the pickup to pass through the field and maintain alignment without sticking to the magnets. Another project for another day.

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    You don't need a capacitor bank discharge magnetizer for Alnico (maybe for ceramic magnets). The commercial magnetizers mentioned above are just electromagnets powered by some 10 ADC. The DC voltage necessary depends on the DCR of the coils. But it's all about Ampere-turns (current times turns' number).

    I built this: https://music-electronics-forum.com/...l=1#post522567
    It produces more than 15.000G between the pole shoes (depending on airgap). Alnico requires up to 3.000G between the poles for saturation. I don't like my bars fully charged, so I only go up to around 2.000G.

    Passing an Alnico bar along Neos inevitably causes a a slanted, uneven magnetizing pattern. The problem with neos is that they can't be switched off, so removing the alnico bar from the neo requires the bar to pass the neos fringe field which is likely to change magnetization.

    I didn't try myself but I think that it is possible to get satisfying results with a single large neo magnet. The neo needs to be larger than the pole face of the alnico bar. Attach the alnico bar to the neo and separate/remove it along the field direction from the neo without any slanting (that's the tricky part). Then reverse both the neo and the alnico bar and charge the other side/pole the same way.

    To control magnetization results you will need a Gauss/Tesla meter.

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    Last edited by Helmholtz; 01-03-2020 at 04:30 PM.
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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by Mick Bailey View Post
    A few years back I read here of a DIY charger that interested me. Similar to commercial units, it used a bank of capacitors discharging into a large coil. I have a pair of very powerful, large neos that I'd intended to use to charge pickups but I've yet to work out how to use them effectively. The trick is to get the pickup to pass through the field and maintain alignment without sticking to the magnets. Another project for another day.
    If you search through JM Fahey's postsI think he described how he made alinico magnets for his speakers in Argentina. Very resourceful guy that I'm afraid we lost. But if you have further questions I think he frequents DIYaudio and ssguitar.
    nosaj

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    Regarding using a neo to charge alnicos, it seems to me that it would be pretty easy to make a jig that would keep things aligned. If you're clever you could probably rig a machine that would bring the neos to a few thousandths of an inch of a pole along the field direction on both ends simultaneously and then distance them evenly the same way. Like a big, levered clamp with stops built in. I don't see that it would be any easier than spending six or eight hundred bucks for a magnetizer (or making your own) but it should work and you might save on your electric bill

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    ToneOholic! big_teee's Avatar
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    Here's the Mojo NEO charger.
    $60


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    Last edited by big_teee; 01-03-2020 at 03:58 AM.


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    The N52 neo magnets I have are 3" diameter and a little over 1 1/4" thick. There's a loading hatch in my workshop 8' off the ground and they live up there, one either side of the sill. They're a real nuisance anywhere else and the pull is 570lb so need to be handled with a lot of respect. I thought they may make a decent magnetizer, though.

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    Regarding using a neo to charge alnicos, it seems to me that it would be pretty easy to make a jig that would keep things aligned.
    When using large steel parts in the jig it should be considered (or measured) how they change and spread the magnetic fields.

    Taping the Neo or using thin spacers/shim will facilitate separation of the magnets. Spacers can also be used to control charge.

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    Quote Originally Posted by big_teee View Post
    Here's the Mojo NEO charger.
    $60

    This is exactly what I used before I built the electromagnet charger. If used with consideration the results with strat type PUs can be ok (though not perfect). Results with bar magnets are disappointing as described above.

    I generally do not like the neos-in-a-vise method. While the magnetic loop through the steel parts can about double the field strength between the neos, it also means that the PU or alnico magnet has to be removed sideways out of a region of strong field. And this typically more or less spoils the magnetization (especially of isotropic alnico bars like A2, A3, A4, UOA5).

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    Last edited by Helmholtz; 01-03-2020 at 05:45 PM.
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    Here you can see an old magnetizer at the Gibson/Elgin (Illinois) string plant:

    img015.pdf

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    Supporting Member mozz's Avatar
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    Pretty much looks like the mag24c. There is a picture out there somewhere of the old Fender shop magnetizer.
    Click image for larger version. 

Name:	mag24c.gif 
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    To me it looks more like this:

    img016.pdf

    From Parker and Studders "Permanent Magnets and their application" 1962/1964.

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    Supporting Member mozz's Avatar
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    Just saying, pretty much the same idea.

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    Quote Originally Posted by mozz View Post
    Just saying, pretty much the same idea.
    Sure, it's just another C-core electromagnet charger like my own build. Moskowitz calls this a "type A" DC electromagnet charger.

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