Help me get my polarity straight ?

Discussion in 'Luthier's Guitar & Bass Technical Discussion' started by SamBooka, Feb 1, 2015.

  1. SamBooka

    SamBooka Member

    Messages:
    2,224
    Joined:
    Dec 8, 2009
    Location:
    Montreal
    So I have a pickup I want to try recharging the magnet for.

    I have a couple of huge neodynium magnets that should work for this

    I have seen the videos, read the articles but one thing I just cant wrap my head around is the polarity (and it seems important enough that I am surprised I dont see it addressed very often)


    Can someone hold my hand for this? Please? :)

    When I put my compass near the top of the pickup (closest to the strings) the part that normally points north points towards the pickup. So I guess this pickups have their south magnetic poles closest to the strings.

    Next. I have two magnets. I lable them the same way I labled the pickup. (if the needle points towards them then that is the south magnetic pole)


    SO now I have labled South on my two magnets and know where south is on my pickup.


    I put one magnet on one jaw of the vice with the south side towards the middle?
    I put the other magnet on the other jaw with the north towards the middle?
    Assuming I have the distance right I pull the pickup between the two magnets with the top (south) towards the north magnet and the bottom (north ) toward the south. If I do this the pickup will want to be pulled towards the magnets right?

    Thanks!
     
  2. Tone_Terrific

    Tone_Terrific Member

    Messages:
    25,013
    Joined:
    Dec 26, 2004
    Location:
    Canada-GTA
    Around here a compass points to the north pole.:huh
     
  3. mark norwine

    mark norwine Member

    Messages:
    16,126
    Joined:
    Jul 25, 2005
    Location:
    NJ...GSP135
  4. mark norwine

    mark norwine Member

    Messages:
    16,126
    Joined:
    Jul 25, 2005
    Location:
    NJ...GSP135
    Yes.

    Couple of things:

    1.) wear the heaviest work gloves you own. These big neo magnets can / will snap together with enough force to break bones if you're unlucky enough to come between them.

    This pic is NOT a staged pic...while I was putting my magnets away, they "bit" me.

    [​IMG]

    2.) My neo mags in my vice. Each pole is four (4) neo magnets "stacked" and wrapped in white gaffers tape. Poles are labeled with sharpies.

    [​IMG]

    [​IMG]



    2.) fold a shirt cardboard around the magnet so that you can control it while it's being charged. Otherwise, you won't get it out!!

    [​IMG]

    [​IMG]


    3.) remember......not kidding! Wear your gloves when working with these magnets!

    [​IMG]


    4.) do NOT smack your neos together...they can shatter. I store mine with a piece of foam in between them....

    [​IMG]

    If you have any more questions, just post them!
     
  5. Tone_Terrific

    Tone_Terrific Member

    Messages:
    25,013
    Joined:
    Dec 26, 2004
    Location:
    Canada-GTA
    So a compass points at a South pole but we call it a North pole geologically and a South pole on a magnet? That is the standard? OK. Thanks. That was a bit unclear.:drink
     
  6. walterw

    walterw Gold Supporting Member

    Messages:
    33,384
    Joined:
    Oct 16, 2006
    do you close up the vise to where the magnets are touching? once you've got the magnet you're charging inside the field there, how long do you let it sit for?

    also, how do you pull it out? just straight up? or do you try to open the vise away from the magnet on both sides?
     
  7. mark norwine

    mark norwine Member

    Messages:
    16,126
    Joined:
    Jul 25, 2005
    Location:
    NJ...GSP135
    Touching, then back it off until it isn't. But it's still as close as can be.

    To the degree that the neos have the strength to do so, the alnico magnet saturates to full charge instantly. Leaving it in longer doesn't increase the strength at all. Of course, if your neos are dinky, you can't charge the bar to its fullest capability; still the alnico will get "all it's gonna get" instantly. But using big neos (like my pics above) will charge the alnico bar fully & instantly.

    I pull straight up. Sometimes you get uneven N vs. S if you rock it up, favoring one side over the other. If that happens and the poles are WAY off, I re-magnetize.
     
    Last edited: Feb 1, 2015
  8. SamBooka

    SamBooka Member

    Messages:
    2,224
    Joined:
    Dec 8, 2009
    Location:
    Montreal
    Thanks all.. it worked!
     
  9. mark norwine

    mark norwine Member

    Messages:
    16,126
    Joined:
    Jul 25, 2005
    Location:
    NJ...GSP135
    how did you measure the strength before & after?
     
  10. SamBooka

    SamBooka Member

    Messages:
    2,224
    Joined:
    Dec 8, 2009
    Location:
    Montreal
    Ears mostly. My non scientific method was how hard it was to pull a flathead away from pickup. It is a strat and the D string on the middle pickup was waaaaay lower in output. On the bridge and neck it was fine but all pickups seemed pretty dead even with the pickups cranked to touching the strings.

    After I did the 3 pickups (so they would be all in the same ball park at least) I had to drop the pickups considerably.. I was getting all the weird harmonics around/above the 12th fret.

    So I "feel" the output has improved across the board and I am certain the D string middle pickup is much better now.
     
  11. mark norwine

    mark norwine Member

    Messages:
    16,126
    Joined:
    Jul 25, 2005
    Location:
    NJ...GSP135
    if this was a one-time effort, then...ok

    But if you want to build a gauss meter for ten bucks, read here:

    http://my.execpc.com/~rhoadley/magmeter.htm

    It's downright crazy how great a setup like this works. You read the DC voltage, and it translates into magnetic strength...
     
  12. SamBooka

    SamBooka Member

    Messages:
    2,224
    Joined:
    Dec 8, 2009
    Location:
    Montreal
    One time things are only one time things until you have to do it again ;)

    I appreciate the link. Will take a look. The only quick and dirty test I had at home that I could have tried is I have a hanging scale that is reasonably accurate. I would have hung a nail off it and measured how much weight the magnet would hold before it let go. It wouldnt be absolute but would give me relative strengths for before/after and to compare with the other pickups.

    I will take a look that your link . If i was really hot and horny I would take the time to test things like this.. https://itunes.apple.com/ca/app/magnetometer/id342782714?mt=8
     
  13. ylo

    ylo Member

    Messages:
    605
    Joined:
    Aug 4, 2006
    Location:
    Ashland, MA
    If I'm not mistaken, the "N" pointer on a compass is actually the south pole of a magnet, so it points to the opposite pole, that is it points north. So the north magnetic pole of the earth should be labeled "N" and south "S" as you would expect. It is the compass pointer itself that is labeled where it points to, not to its actual polarity.

    For pickups, doesn't matter as long as you get them lined up with each other correctly . . . unless of course you want to use your guitar for navigation.
     
  14. walterw

    walterw Gold Supporting Member

    Messages:
    33,384
    Joined:
    Oct 16, 2006
    mark n's link suggests the exact opposite!
    the linked article describes the compass pole with the "N" embossed on it, the one that points towards the arctic circle, as a "north-seeking" pole, and defining that as a "north pole" on a magnet.

    this means the earth's magnetic pull at the arctic circle is actually a magnetic south pole, and now i'm totally scrambled.
     
  15. mark norwine

    mark norwine Member

    Messages:
    16,126
    Joined:
    Jul 25, 2005
    Location:
    NJ...GSP135
    Actually, now you "get it"....
     

Share This Page