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Silencing a humming transformer ( + ACDC adaptor that blew )

Discussion in 'Electronic Repair' started by [email protected], Feb 28, 2007.

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  1. Guest

    I have no experience with electronics except dabbling with a
    multimeter.

    I wanted to silence a humming transformer, I read somewhere that
    covering it in JB Weld would do the job. But I didn't even get that
    far.

    I struggled to open it up, in the end I managed it quite 'easily' with
    a hammer.

    Before even putting on any JB Weld, I put the lid back on it and
    plugged it in.

    Then I flicked the mains power switch and bang it blew.

    I know it was the ACDC adaptor because and not a mains plug fuse
    because the power cord still worked in another ACDC adaptor

    Is there a way for me to open one of these things without encountering
    that?
    does anybody know about silencing humming / whining transformers
     
  2. I think You were quite sucessful in your effort to silence that
    transformer! Using a hammer was very creative! I have found that a
    hammer is usually not effective way to get into those things, so you
    surely had a big hammer. Perhaps it would be safer to buy a new one. For
    future reference, you can often silence a noisy transformer with a small
    shim or wooden toothpick between the core and the windings. Dont use so
    much force that you cause the wires to short out or break. Noisy
    transformers can also mean that there is a bad diode or electrical
    short. This may cause a safety issue. Repairing "wall warts" or AC/DC
    adaptors is seldom worth the cost and is often unsafe.

    --
    Joe Leikhim K4SAT
    "The RFI-EMI-GUY"©

    "Treason doth never prosper: what's the reason?
    For if it prosper, none dare call it treason."

    "Follow The Money" ;-P
     
  3. Guest

    first eliminate overload/shorting as a possible cause of hum. Then any
    of the following:
    wedges between core and bobbin
    hit the edge of the core with a hammer & cold chisel to jam the lams
    together
    put glue or tar on the lam edges

    NT
     
  4. PeterD

    PeterD Guest


    Man, I'll get blasted for this one!

    Drill two small holes (carefully) into the case, near the edges.

    Position with holes up.

    Mix up some epoxy.

    Inject the epoxy into one of the holes until it comes out the other
    one.

    (alternative: one of those devices that both mixes and injects the
    mix.)

    Wait for a few hours after the epoxy sets to test.

    No warranties expressed or implied on this one... <bg>
     
  5. Did anyone notice he was using JB Weld epoxy? I think that stuff has
    metal particles in it!
    --
    Joe Leikhim K4SAT
    "The RFI-EMI-GUY"©

    "Treason doth never prosper: what's the reason?
    For if it prosper, none dare call it treason."

    "Follow The Money" ;-P
     
  6. Guest

    I haven't used it yet. I have a few cheap rubbish ACDC adaptors most
    or all of which make a noise. I broke one as described, but i'll try
    to experiment on the others too.

    http://jbweld.net/products/jbstik.php
    it says it's an insulator.

    I will reply to my post with links to pictures of the transformer.

    <snip>
     
  7. James Sweet

    James Sweet Guest


    Regardless there's a lot easier epoxies to use. JB Weld is very thick
    paste, you can get liquid epoxy resins which will be much easier to pour
    into something.
     
  8. Guest

    Here are pictures of the transformer
    http://img152.imageshack.us/img152/262/15084473gh0.jpg
    http://img339.imageshack.us/img339/954/18933823la0.jpg
    http://img339.imageshack.us/img339/3033/19265605dw7.jpg

    I know the AC-DC adaptor sits on a book about electricity, but it
    hasn't been read, I don't have any background in the subject!
     
  9. Guest

    thanks for the tip, i'll be getting some.
    I posted some pictures of the transformer, I can't really get to it..
    The copper coils of wire seem to be covered in some yellow thing and
    aroudn the whole thing there's this square housing with yellow tape
    over it.

    But, just to get an idea of where i'd pour the stuff.. if I could.
    Here is a picture of another device I once had. The transformer was
    'naked'.

    It was a power supply card.
    http://linitx.com/product_info.php?products_id=397
    you can click the image to enlarge it.
    Alternatively here it is
    http://img72.imageshack.us/img72/38/aazc0.jpg
    There were a couple of transformers on it as you can see.

    I think if the transformer is shaped like a doughnut. With my AC-DC
    adaptor, the wires go round in circles that are sort of parallel with
    the PCB. They go round the circumference of the doughnut. (at last I
    think that's what they do, i'd have to pull off the housing to get a
    better look)

    Whereas on the power supply card that I linked to, the wires are sort
    of perpendicular to the PCB.

    In the case of the power supply card, would I pour liquid epoxy in the
    middle. WHat is actually causing the hum? The coils hitting the
    doughnut(core?)


    I just googled transformer coils core into google images. And got this
    amazing picture
    http://img.alibaba.com/photo/11498927/Transformer__Coils__Inductor__Line_Filter.jpg
    or for the archives
    http://img135.imageshack.us/img135/3100/transformercoilsinductooq8.jpg

    I see the one in my AC-DC adaptor in that picture. It's second row
    from the back. And second , maybe third, from the left !!
     
  10. It does say it has "steel reinforcement" in it. To what extent it might
    mess with a linear or swiching power supply, I couldn't guess. I would
    use a different epoxy if in doubt.

    --
    Joe Leikhim K4SAT
    "The RFI-EMI-GUY"©

    "Treason doth never prosper: what's the reason?
    For if it prosper, none dare call it treason."

    "Follow The Money" ;-P
     
  11. John E.

    John E. Guest

    I've heard that using a light oil (be sure to find one that doesn't stink!)
    -- just a few drops -- will lubricate between the lams and quiet a hummer.

    Good luck,
     
  12. Arfa Daily

    Arfa Daily Guest

  13. Ross Herbert

    Ross Herbert Guest

    Unless I'm mistaken the transformer you refer to is a fairly standard
    E core ferroxcube switch mode type. The cores are generally stuck
    together with epoxy or other suitable adhesive at manufacture. If the
    adhesive between the faces of the two E cores comes adrift you will
    hear a high pitched squeal and possible even a rattle. I would not try
    to fix this by covering it with any sort of gunk (or JB Weld). The
    transformer should be unsoldered from the board and the two E cores
    removed, their mating faces scraped clean and then re-glued under
    pressure.

    Sometimes only one face may have come unglued so you have to heat the
    transformer core to a reasonably high temperature (I use a hot air
    gun) in order to soften the remaining bonds so you can get the cores
    apart.

    Re-gluing with epoxy adhesive is good and will definitely fix your
    squealing transformer. I have also used Cyanoacrylate (superglue) to
    rebond core faces.
     
  14. default

    default Guest

    We used aluminum filled epoxy to make nearly bulletproof modules for a
    military contractor. The aluminum made it transfer heat well - but
    some of the modules would fail the high potential test as a result of
    the metal content.

    An unfilled epoxy would be safer. or mix some non- conductive non
    flammable filler in like sand or chopped glass or ceramic micro
    balloons,
     
  15. PeterD

    PeterD Guest

    I don't think JB Weld had metal in it, but I've seen metal in epoxy
    cause some rather interesting problems! <bg>
     
  16. James Sweet

    James Sweet Guest

  17. Jim Land

    Jim Land Guest

    Switchmode power supplies do not hum. (Where "hum" is defined as a 50 or
    60 Hz, or 100 or 120 Hz sound.) They operate at much higher frequencies.
    Which is the whole point of a switchmode power supply: higher frequency
    means less iron.

    Original poster: What did you hear from this power supply that got this
    whole thing started? Describe the sound.
     
  18. Guest

    here's a recording , putting my mic near it
    it's an mp3 file about 1 minute long
    http://tinyurl.com/3xsuay

    around 11-15sec is probably most representative, i.e. quite high
    pitched. Though it's quite a bit higher than the recording has it.
     
  19. Guest

    putting aside the fact that it may be a capacitor humming. I may have
    other devices with transformers like that and they may hum. How and
    where would I put anything into that transformer? The transformer is
    surrounded in an outer casing.
    I tried soldering the transformer off (was a cheap acdc adaptor and
    that particular one I had was already blown). It didn't come off, so,
    I plied it off with a screwdriver, for the sake of getting a better
    look at it. Either way, whether it's on the board or off it, I can't
    see where i'd be putting the epoxy. The whole thing is surrounded in a
    square shell.

    I linked to a pic of it here
    http://img135.imageshack.us/img135/3100/transformercoilsinductooq8.jpg
    second from left second row from back.


    And is a noisy capacitor solved with epoxy?

    thanks
     
  20. Guest

    Guest Guest

    put the adapter in the refrigerator for an hour or two

    find the seam that closes the outer halves.

    lay the thing on a concrete surface, (it must be absolutely non-movable)

    gingerly whack exactly on the seam, go rouund it a few times

    most ultrasonically welded units will fracture at the seam, some chemically
    bonded will refuse to open, they require a jewelers hacksaw to splitt the
    case.

    whenu get inside, dip the xformer in a good brand of varnish, then bake the
    thing for a couple hours at 250F in an oven

    most buzzing is caused by poorly wound (looselywound) wires around the core
    that migrate as the unit experiences warm/cool cycles. some thinly applied
    manufacturing varnishes fail easily and then the insulating varnish on the
    actual coper wire wears and then you get a nice short that often will
    entertain u with a bang or flash or complete destructive fire of your
    home/business ;-))

    all good reason to buy good adapters whenever u can
     
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