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Thread: My new pickup magnetizer

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    My new pickup magnetizer

    Build this pickup magnetizer some time ago, able to magnetize to 24000 Amp/Turns, this thing rocks

    Click image for larger version. 

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    Pickup Maker David Schwab's Avatar
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    That looks very nice!

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    Quote Originally Posted by Claus H View Post
    Build this pickup magnetizer some time ago, able to magnetize to 24000 Amp/Turns, this thing rocks

    Click image for larger version. 

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    I covet.....

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    Quote Originally Posted by jack briggs View Post
    I covet.....
    Thanks guys
    Thinking about doing a full diy instructions, it's not that complicated a build, just the fact it's designed for Danish mains power (230VAC) With a variac..

    We use it to magnetize our production pickups at hansen with great results, dialing in the just right amount of gauss

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by Claus H View Post
    Thinking about doing a full diy instructions, it's not that complicated a build, just the fact it's designed for Danish mains power (230VAC) With a variac.
    Nice looking machine Claus! Thanks for letting us have a look. I think many of us would like to be enlightened with your diy instructions. Don't worry we can get 220-240 VAC in the USA even if it means we string a very long extension cord to Denmark. Also it may be easy enough to adapt to 120VAC power.

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    Quote Originally Posted by Claus H View Post
    Thinking about doing a full diy instructions, it's not that complicated a build, just the fact it's designed for Danish mains power (230VAC) With a variac.
    Is this a big coil powered by a full-wave rectifier bridge powered by the variac? If so, use of a slightly thicker diameter of wire (area of copper cross-section doubles) and use of the correct variac is all the adaptation needed.

    One common dodge is to use two windings: In series, 220 Vac. In parallel, 120 Vac. But be sure to connect the coils such that the fields add.

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    Hi Claus

    Yes please. A diy build would be great. No problem with the mains here in Austria.

    Cheers

    Andrew
    Quote Originally Posted by Claus H View Post
    Thanks guys
    Thinking about doing a full diy instructions, it's not that complicated a build, just the fact it's designed for Danish mains power (230VAC) With a variac..

    We use it to magnetize our production pickups at hansen with great results, dialing in the just right amount of gauss

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    Quote Originally Posted by Joe Gwinn View Post
    Is this a big coil powered by a full-wave rectifier bridge powered by the variac? If so, use of a slightly thicker diameter of wire (area of copper cross-section doubles) and use of the correct variac is all the adaptation needed.

    One common dodge is to use two windings: In series, 220 Vac. In parallel, 120 Vac. But be sure to connect the coils such that the fields add.
    It's two coils wired in series, two coils of 4000 turns of 0.4mm wire, on a 150mm long, 25mm diameter, soft iron core, powered from a full-wave rectifier bridge of the variac, a few tricks to get the digital readout working. Schematic comming up.. It's all build into variac case..

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    Old Timer J M Fahey's Avatar
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    Schematic and mechanical drawing please

    Just curious: whatīs the frontal area of the bevelled adjustable ends of the yoke?

    I hope itīs equivalent to (or smaller than) the 25 mm dia. rod area.

    And, are you running 3A through those 0.4mm wires?

    Rectified unfiltered 240VAC into thay coil which I calculate around 120 ohms would provide around 2A.

    Adding supply caps would add some 50% more, if ripple is low.

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    Last edited by J M Fahey; 06-01-2014 at 03:12 AM.
    Juan Manuel Fahey

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    I'm assuming it's not a capacitive discharge magnetizer and that you just turn it on and off quickly, right?

    I had one like that at Alembic as our first...a home-brew unit; then we went to a big surplus capacitive discharge machine.

    Love to build one like you show.

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    Quote Originally Posted by J M Fahey View Post
    Schematic and mechanical drawing please

    Just curious: whatīs the frontal area of the bevelled adjustable ends of the yoke?

    I hope itīs equivalent to (or smaller than) the 25 mm dia. rod area.

    And, are you running 3A through those 0.4mm wires?

    Rectified unfiltered 240VAC into thay coil which I calculate around 120 ohms would provide around 2A.

    Adding supply caps would add some 50% more, if ripple is low.
    Will be posting a mechanical drawing with mesurements, and yes i am running close to 3A through coil, my variac, can provide 270VAC, the resistance of the coils are 56 ohms, no supply caps are used, thinking about trying it but, it does provide enough power, to fully magnetize A5 rods and bars..
    The frontal area of the bevelled ends are not calculated, but dimensioned to fit guitar pickup, but now you mention it, I will try some different sized "yokes"

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    it's not a capacitive discharge magnetizer, it's just turned on by a momentary switch, as long you push it, is ON

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    Quote Originally Posted by Claus H View Post
    it's not a capacitive discharge magnetizer, it's just turned on by a momentary switch, as long you push it, is ON
    How long till fire and brimstone?

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    Quote Originally Posted by Joe Gwinn View Post
    How long till fire and brimstone?
    It does not heat up that much, had it running for 10 min at 220VAC without anything burning, you can magneticze magnets all day, as long as you don't hold down the switch continuously but you could build in a tempfuse in the coil..

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    Quote Originally Posted by Claus H View Post
    it's not a capacitive discharge magnetizer, it's just turned on by a momentary switch, as long you push it, is ON
    Thanks.

    I'm asking about practical details because I have already designed and built 2 speaker magnetizers which I have been using for the last 15 years and I'm starting on the third one,but it's always nice to see what others are doing.
    Not much usable info available, by the way, so evry bit helps

    And I also went the "brute force" path, no useful capacitors available in quantity here .

    My first one is for up to 105 mm diameter ceramic magnets and uses rectified 220V @ 25 amperes and the larger one 3 x 380V rectified at 40A , good for 150mm magnets.
    And now I'm building one for 190/220mm ones, to clone EV/JBL types but I'm stalled because have not yet decided on the power source.
    Brute force needed is more than what I have available and don't have enough big caps so .....
    Oh well.
    If Life were easy it would be boring, isn't it?

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    Juan Manuel Fahey

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    Quote Originally Posted by J M Fahey View Post
    And I also went the "brute force" path, no useful capacitors available in quantity here .
    Do you have three phase power available?

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    Joe, I do; I have tons...well, many amps...available @480 V or 208 V; I've used both on various machines in my shop.

    How would that help given that you're slamming the magnetizer coils with DC? Is there an interesting rectifier circuit for 3 phase to big DC? And a circuit for capacitive discharge would be great.

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    Quote Originally Posted by J M Fahey View Post
    Schematic and mechanical drawing please

    Just curious: whatīs the frontal area of the bevelled adjustable ends of the yoke?

    I hope itīs equivalent to (or smaller than) the 25 mm dia. rod area.

    And, are you running 3A through those 0.4mm wires?

    Rectified unfiltered 240VAC into thay coil which I calculate around 120 ohms would provide around 2A.

    Adding supply caps would add some 50% more, if ripple is low.
    Schematic Click image for larger version. 

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    Quote Originally Posted by Rick Turner View Post
    Joe, I do; I have tons...well, many amps...available @480 V or 208 V; I've used both on various machines in my shop.

    How would that help given that you're slamming the magnetizer coils with DC? Is there an interesting rectifier circuit for 3 phase to big DC? And a circuit for capacitive discharge would be great.
    What comes out of a single-phase fullwave rectifier bridge is halfcycles at 120 Hz, which has a lot of harmonics, and will heat the iron and is somewhat self-defeating for a magnetizer. A filter capacitor helps a lot. Not that people don't just brute-force it and life goes on.

    Juan said that it was hard to get big filter capacitors in Buenos Aires. Well, if you have three phase, a three-phase bridge rectifier bridge (which can be bought or made at home using six rectifier diodes) will make pretty clean DC all by itself, without the need for filter capacitors. I'd use 208 Vac, not 480 V (which requires all manner of special handling for safety) And make sure that the case is made of metal, and is solidly grounded to the safety (green) ground. If something shorts out, it's best if the breaker pops, not the user.


    As for the capacitive discharge magnet charger, that's a very different kettle of fish. While I did publish the patent number of a good circuit, it came with a draconian warning. Just to be clear, a capacitive discharge magnet charger is quite capable of boiling the grease out of the unwary. There is a lot of energy stored in that capacitor bank. Small ones have the same stored energy as the defibrillators used in hospitals. This really does require someone with formal training in electronics to implement, and it isn't clear that there is much money to be saved by DIY approaches because most of the money is in big power components. I'd try to find a used unit instead.

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    Pickup Maker David Schwab's Avatar
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    Quote Originally Posted by Joe Gwinn View Post
    Just to be clear, a capacitive discharge magnet charger is quite capable of boiling the grease out of the unwary.
    That's quite a visual right there!

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by Joe Gwinn View Post
    Just to be clear, a capacitive discharge magnet charger is quite capable of boiling the grease out of the unwary.
    Like that turn of phrase Joe! With that in mind...

    For cap discharge types would it not make sense to use film caps not electrolytic, also a "hockey puck" SCR or Triac as a switch? Lab upstairs from mine in college was trying to do some basic experiments in fusion @ 1975 - they invested in a truckload of surplus el caps, and turned their mechanical switch into vapor the first time they tried to run a pulse thru their magnet coils. The guy who operated the switch survived all right but couldn't hear for a week (sounded like a small cannon went off from my lab) and got splattered with red hot metal beads. Later they found a lot of the el caps going bad fast due to instant discharge. OK, a pickup magnetizer need only be 1/1000 as powerful but I'll never forget that debacle. Trying to think safety, plus a good service life for the caps.

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    Quote Originally Posted by Leo_Gnardo View Post
    For cap discharge types would it not make sense to use film caps not electrolytic, also a "hockey puck" SCR or Triac as a switch?
    For film caps, one cannot get as much capacitance, so one instead goes for voltage, as stored energy varies with the square of voltage. Commercial units use from 2,000 to 5,000 volts. The voltage is chosen by a tradeoff between the cost and capacitance of capacitors versus voltage.

    For electrolytic caps, the max working voltage is something like 400 Volts (using caps rated for 450 Vdc), but one can get a lot of microfarads per dollar, but reverses voltage causes instant destruction.

    Hocky-puck SCRs (not triacs) are the standard way to go, due to their surge capacity.


    Lab upstairs from mine in college was trying to do some basic experiments in fusion @ 1975 - they invested in a truckload of surplus el caps, and turned their mechanical switch into vapor the first time they tried to run a pulse thru their magnet coils. The guy who operated the switch survived all right but couldn't hear for a week (sounded like a small cannon went off from my lab) and got splattered with red hot metal beads.
    Glad no permanent damage. Sounds like some back of the envelope calculations were needed. Not to mention a series of tests starting at 5% voltage.


    Later they found a lot of the el caps going bad fast due to instant discharge. OK, a pickup magnetizer need only be 1/1000 as powerful but I'll never forget that debacle. Trying to think safety, plus a good service life for the caps.
    Yeah. There are a number of considerations, and risetime is one of them (too quick and eddy currents in the alnico prevent full magnet charging). As is peak surge current.

    As is resonance: The charger is a big capacitor connected to a small coil (which generates the magnetic field), and so rings, the voltage on the big capacitor reversing periodically. Reversal will blow an electro immediately, and greatly shortens the lifetime of film caps if done at full power, so the charger circuit must prevent reversals. The patent whose number I published some time ago does just that, and is intended for electros.

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    Joe, something like this?: 80A 80 Amp 3-Phase Three Phase Bridge Rectifier AC to DC

    Or bigger?

    I would imagine that I've got several of these inside my CNC machine...

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    Last edited by Boss; 03-10-2019 at 10:51 AM.

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    Quote Originally Posted by Rick Turner View Post
    Joe, something like this?: 80A 80 Amp 3-Phase Three Phase Bridge Rectifier AC to DC

    Or bigger?

    I would imagine that I've got several of these inside my CNC machine...
    That sounds like it will work, although no datasheet is provided.

    It would be difficult to run at anything resembling 80 amps at 220 volts (17,600 watts) because the coil would melt. Actually, boiling copper would spray out the cooling vents.

    Anyway, a proposed design is needed before any real evaluation is possible.


    Do not try this at 480, even though the rectifier is rated for 1000 volts, because handling 480 requires real engineering knowledge to use safely.

    Let me put it this way: Below about 300 volts, if an arc starts (say by a tin whisker), there will be a pop and the arc will self extinguish. Above, the arc will not self-extinguish, and the arc will continue until something external stops the drama. This has many consequences, one of which is that one does not have panel switches controlling 480 V, one has a full-size contactor controlling the 480, the contactor (running at 110 or lower) being controlled by a front-panel switch, all in a well-grounded stout steel box.

    And then there is arc flash: Arc flash - Wikipedia, the free encyclopedia


    More generally, one should follow the National Electrical Code (NEC), NFPA 70. Not to put too fine a point on it, but the NEC is written in blood.

    War story from my Grandfather: There was an industrial concern where my Grandfather worked. A workman touched an electrical box, and was instantly electrocuted. The brass gathered to investigate, and one of the dead workman's fellows explained that what had happened was that the unfortunate fellow had only touched this box. Unfortunately, the second fellow demonstrated what the first fellow had done, and he too was struck dead. Two men down. Not a good day.

    Root cause: In the old days, people believed that one could isolate the stuff inside from the box, and this would be good enough. There were many stories like this one, and eventually the NEC (or its predecessor) was changed to require that all electrical boxes be solidly grounded. This has worked far better.

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    Last edited by Boss; 03-10-2019 at 10:51 AM.

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    I'm pretty good at red wire to red wire, white to white, black to black, blue to blue, green to green, but I do not want molten copper anywhere near me! Obviously there has to be some current limiting built in there somewhere. I would imagine that the lower voltage would let the coil resistance (and inductance) work favorably to prevent a major mishap. I've got 208 available, too. I do like the idea of the smoother DC from 3 phase rectification. There must be timer switches that one could calibrate for something like this.

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    Hmmm, a nice Dr. Frankenstein's Lab large three bladed knife switch would be utterly bitchin'! The bigger the better. Then make a nice Plexiglas cover for it... Tesla coil humming in the background... Or just discharge the Tesla coil into the pickup zapper coils.

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by Rick Turner View Post
    Hmmm, a nice Dr. Frankenstein's Lab large three bladed knife switch would be utterly bitchin'! The bigger the better.
    Love those old Frankenstein switches! So many have gone to the recycler, lotta copper there. But one might be practical for a reasonable size magnetizer, might be able to scour one up in the antique shops or ebay.

    Yes important to get the colors right. One fine day in a South Bend theater the house 'lectrician wasn't too careful and swapped the blue and green. I was about to point out . . . when he threw the switch. Some serious welding went on, shooting BIG sparks. Woops. Maybe he had to replace a couple cam-locks but the show went on.

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    Old Timer J M Fahey's Avatar
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    Answering a few questions.

    1) My home magnetizer is single phase.
    As said before, 220V rectified (which amounts to some 180V "mean/average"? (in Spanish the same word "valor medio" applies to both, depending on context) ,25 Amperes.
    No, no molten copper, even less flying droplets, in spite of the 220x25=5500W rating because it has a HUGE thermal mass (some 6 lb 2 mm copper wire) and duty cycle is less than 1% : 5 seconds magnetizing , batches of 10/15 speakers tops.
    Of course, if I let it "on", it would probably catch fire in less than 15 minutes ... but that amounts to some 150 speakers or more ... not in my wildest dreams.
    I was not referring to filter caps, magnetizers are the world's largest choke input power supplies with a huge time constant, measured in seconds.
    Puny 100Hz ripple pales before that.
    In fact, current buildup is above 2 or 3 seconds (hence the 5 seconds "on" time), then I can't pull the speaker after 5 or 6 seconds until the residual current lowers enough.
    Yes, it's a big inductor.
    I need *a ton* of capacitors not for filtering but for a capacitive discharge one.
    The cap bank cabinet is small fridge size.

    2) the three phase one lives at a friend's factory, who has 3x380V power.
    Full wave rectified 380V has very little ripple, even if unfiltered.
    I use a huge Siemens contactor, meant to start big motors, switching the **AC** side of things which is doable, switching DC would be close to impossible.
    380Vx40A = 15KW but as before there's a lot of thermal mass, that machine has some 60 lbs copper tightly wound on some 400 lb core and duty cycle is also very low.
    It has so much inductance that current rise is easily seen on a needle ammeter, so slow (say 5 or 6 seconds) that although max current is around 46A, we stop when the needle reaches 40A, both for uniformity and to minimize heating.

    Both coils (home and factory) have flyback diodes whic make turning OFF much easier.
    And both have been flawlessly in operation for 20/25 years, already lost count.

    Now the next BIG one is scaring me, whether brute force or CD.

    Although I'm mulling making it a different shape: instead of making the big monster (I actually need the same magnetizer as JBL or EV, magnets follow Physics Laws and couldn't care less I am a pygmy compared to them) which can magnetize a finished speaker inside the shipping box, while I'll probably make a closed box magnetizer, *only* for the magnetic assembly, no frame or anything else (this reduces needed power by 80% because of the much reduced magnetic path) and later bolt the pre-magnetized assembly to the frame.

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    Last edited by J M Fahey; 06-03-2014 at 07:54 AM.
    Juan Manuel Fahey

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    Quote Originally Posted by Rick Turner View Post
    I'm pretty good at red wire to red wire, white to white, black to black, blue to blue, green to green, but I do not want molten copper anywhere near me! Obviously there has to be some current limiting built in there somewhere. I would imagine that the lower voltage would let the coil resistance (and inductance) work favorably to prevent a major mishap. I've got 208 available, too. I do like the idea of the smoother DC from 3 phase rectification. There must be timer switches that one could calibrate for something like this.
    It's OK if you stick to 208 three phase. Things are a lot quieter. And an interval timer is a very good idea, for repeatability and equipment safety both.

    But don't forget the grounded metal box.

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    Quote Originally Posted by J M Fahey View Post
    Answering a few questions.

    1) My home magnetizer is single phase.
    As said before, 220V rectified (which amounts to some 180V "mean/average"? (in Spanish the same word "valor medio" applies to both, depending on context) ,25 Amperes.
    No, no molten copper, even less flying droplets, in spite of the 220x25=5500W rating because it has a HUGE thermal mass (some 6 lb 2 mm copper wire) and duty cycle is less than 1% : 5 seconds magnetizing , batches of 10/15 speakers tops.
    Of course, if I let it "on", it would probably catch fire in less than 15 minutes ... but that amounts to some 150 speakers or more ... not in my wildest dreams.
    I was not referring to filter caps, magnetizers are the world's largest choke input power supplies with a huge time constant, measured in seconds.
    Puny 100Hz ripple pales before that.
    In fact, current buildup is above 2 or 3 seconds (hence the 5 seconds "on" time), then I can't pull the speaker after 5 or 6 seconds until the residual current lowers enough.
    Yes, it's a big inductor.
    None of us were thinking anywhere near as big as this. How many turns of 2mm wire is that? What are the coil and core dimensions?

    For "valor medio" in Spanish, both average and mean are correct translations into English, and are used interchangeably.


    I need *a ton* of capacitors not for filtering but for a capacitive discharge one.
    The cap bank cabinet is small fridge size.
    What's the voltage and capacity?

    If I recall, it was to you that I provided the patent number. Is this an implementation of that patent?


    2) the three phase one lives at a friend's factory, who has 3x380V power.
    Full wave rectified 380V has very little ripple, even if unfiltered.
    I use a huge Siemens contactor, meant to start big motors, switching the **AC** side of things which is doable, switching DC would be close to impossible.
    380Vx40A = 15KW but as before there's a lot of thermal mass, that machine has some 60 lbs copper tightly wound on some 400 lb core and duty cycle is also very low.
    It has so much inductance that current rise is easily seen on a needle ammeter, so slow (say 5 or 6 seconds) that although max current is around 46A, we stop when the needle reaches 40A, both for uniformity and to minimize heating.
    And this is even larger than the first: from 6 pounds of copper to 60 pounds.

    If 300 Vdc causes current to rise from zero to 40 amps in 5 seconds. If I'm understanding, that's 37.5 Henrys. This is a pickup for infrasonic waves from the ionosphere.

    Both coils (home and factory) have flyback diodes which make turning OFF much easier.
    And both have been flawlessly in operation for 20/25 years, already lost count.
    The reason that those units have worked for all these years is that those diodes prevented inductive spikes from puncturing the wire insulation.

    There is a lot of stored energy in that inductor, and it will generate whatever voltage it needs to dump the energy: 37.5/2*(40)^2 = 30,000 Joules.


    Now the next BIG one is scaring me, whether brute force or CD.

    Although I'm mulling making it a different shape: instead of making the big monster (I actually need the same magnetizer as JBL or EV, magnets follow Physics Laws and couldn't care less I am a pygmy compared to them) which can magnetize a finished speaker inside the shipping box, while I'll probably make a closed box magnetizer, *only* for the magnetic assembly, no frame or anything else (this reduces needed power by 80% because of the much reduced magnetic path) and later bolt the pre-magnetized assembly to the frame.
    You're the expert here, but isn't assembly of a magnetized assembly a bit of a time sink, which is expensive in production?

    Well, the pattern is clear: first unit has 6# of wire, second unit has 60#, so next unit needs 600#.

    We're getting into a region where a capacitive discharge charger may be cheaper.

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  32. #32
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    Here a little teaser, I finished the layout in 3D, now I just need to do up some real, mechanical drawing with mesurements, from the 3D stuff, and you will have what you need to build this magnetizer..
    By the way J M Fahey the frontal area of the bevelled yokes are exactly the same size as the core of the coil, strange coincidence 490mm2 Luck I quess
    Click image for larger version. 

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    Old Timer J M Fahey's Avatar
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    Well, so much for trusting 25 y.o. memories

    Last night I did the logical thing and went measure the actual magnetizer at home (the other one is 30 miles away )
    The wire is much thinner, closer to 1 mm from the pigtails I see.
    No, canīt get a caliper inside , no space for it
    The DC resistance is exactly 5 Ohms so current is higher: 180V/5ohms=36A
    Which amounts to 36x180=6500W

    The 2mm wire memory refers to the other one , which now that I remember was wound with dual 2mm wire in parallel; a thicker one would have been much harder to wind.
    A monster.
    Talk about brute force.

    As I said before, it doesnīt matter that Iīm a tiny 50 speaker a month maker, I need the exact same magnetizing power as Jensen, Eminence, EV or Celestion if I want to clone their speakers ... which Iīm doing .

    As of .... is it worth the effort? consider this: I have been making guitar amps since 1969 ...... and NO , repeat NO guitar speakers have been available here until the late 90's.

    Everybody here used a Hi Fi woofer for Bass (quite acceptable) and a Hi Fi "extended range" for guitar: unbearably buzzy.
    And if they used the woofer, it was bearable but dull.

    So being a trained Engineer with experience in different Industries I took the bull by the horns.

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    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by Claus H View Post
    Schematic Click image for larger version. 

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    Dear claus H , thanks for posting.

    Well, you did it right

    I asked about the yoke front surface because the iron path is critical: where itīs thinner it becomes closer to saturation (or straight saturates ) and it behaves like air (or vacuum), your worst enemy. (resistive loss).

    And if the yoke is wider that the core, it spreads so the flux density goes down the drain.

    So keeping iron section nearly constant along the path is the most efficient

    As of your 24000 A.t. itīs WAY over whatīs needed for Alnico (which is "easy") and ample for ceramics, so be certain you will saturate *any* magnet you may use in a pickup

    You are miles ahead of any "passive" magnetizer, except, perhaps, one carrying powerful rare earth ones.

    And having a Variac in the power supply means you can exactly duplicate any vintage worn one, if you need to get a particular vintage sound

    I have different needs, I need as much saturation as possible.
    Not much appreciation around here for old worn Alnico speakers .

    Thanks again for posting

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    Thank you.. And thanks for the info on the yokes, I did not know that, love to learn new things, but have had experience with saturation, in transformers, and yes i do believe that I have enough for any guitar pickup.. I really need to get a look at the speakers you build Have a nice day
    Claus Holm Jensen

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