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  • #31
    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.

    Comment


    • #32
      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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      • #33
        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.
        Juan Manuel Fahey

        Comment


        • #34
          Originally posted by Claus H View Post
          Schematic [ATTACH=CONFIG]29114[/ATTACH]
          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
          Juan Manuel Fahey

          Comment


          • #35
            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

            Comment


            • #36
              Thanks.
              Hereīs a couple, the standard day to day breadwinners:
              G12 side by side with a Celestion Greenback for comparison.
              Of course I usually sell mine inside cabinets, or to fellow ampmakers, so didnīt care too much about fancy covers or even labels, or pretty color schemes, they're quite utilitarian:


              Same from back:


              One workday product:


              Already zinc plated frames, waiting for the ceramic magnets, polepiece and backplate.
              Forward stack 10" frames, back ones 12" in different versions (A Jensen type and a Celestion type) :
              Juan Manuel Fahey

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              • #37
                Originally posted by J M Fahey View Post
                Thanks.
                Hereīs a couple, the standard day to day breadwinners:
                G12 side by side with a Celestion Greenback for comparison.
                Of course I usually sell mine inside cabinets, or to fellow ampmakers, so didnīt care too much about fancy covers or even labels, or pretty color schemes, they're quite utilitarian:


                Same from back:


                One workday product:


                Already zinc plated frames, waiting for the ceramic magnets, polepiece and backplate.
                Forward stack 10" frames, back ones 12" in different versions (A Jensen type and a Celestion type) :

                Cool stuff gotta try them someday
                We build guitars hansen mostly relic stuff, I have been designing pickups for 5 years now, came from a electronics background... I think they sound good now

                Comment


                • #38
                  Hey !!!! Cool guitars!!!
                  And find incredibly accurate the "aging" process.
                  You donīt own a Time Machine, do you?
                  Juan Manuel Fahey

                  Comment


                  • #39
                    Originally posted by J M Fahey View Post
                    Hey !!!! Cool guitars!!!
                    And find incredibly accurate the "aging" process.
                    You donīt own a Time Machine, do you?
                    Thanks we do our best.. Yes we have a time machine
                    Have a nice weekend
                    Claus

                    Comment


                    • #40
                      Mechanical drawing with mesurements nearly done..
                      Click image for larger version

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                      • #41
                        Mechanical drawing with mesurements.....

                        Click image for larger version

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                        Hope you can use them..

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                        • #42
                          Another one...
                          Click image for larger version

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                          Happy xmas
                          Claus

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                          • #43
                            Hi Claus

                            Do you use any kind of mild steel for the poles or do you have a particular requirement for pure iron ?

                            Cheers


                            Andrew

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                            • #44
                              Would ferrite work? Soft, aka electrical iron is hard to come by. Maybe 1010 will be close enough.

                              Comment


                              • #45
                                1010 is perfect.

                                Ferrite has much lower saturation point, and "stays magnetized" so as soon as you turn current off "it works against you" .

                                In fact 1010 is hard to get by, being so despised (for its mechanical properties) so in practice 1018 is an acceptable substitute if you can get nothing milder.
                                Juan Manuel Fahey

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