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Thread: OT: Transformer Buzz

  1. #1
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    Default OT: Transformer Buzz

    I have several of these Trip Lite Smart1300LCDT UPS power supplies:
    https://www.tripplite.com/support/smart1300lcdt

    Most of them got dropped and beat senseless by UPS in shipping. All but one seems ok.
    They all buzz a tiny bit if you listen closely, but one of them buzzes much more loudly than the rest - that HF buzz like an old tv. Everything looks fine inside and it seems to be the transformer making the noise. All screws are tight and the mounts are intact, I see nothing else wrong and it passes the self-test.

    Why is it buzzing, and should I care?

  2. #2
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    The transformer laminations may have loosened up. They are typically dipped in lacquer or epoxy to keep them tight. It may also be possible for grain-oriented silicon steel to lose some of its magnetic properties due to shock, which might change the inductance and thus the quiescent current. You might see differences in line current, especially viewing the waveform on a scope. Saturation due to lower inductance will probably show up as current peaks. If you have a variable transformer (Variac or Powerstat), see if the buzzing diminishes as you lower the voltage.

  3. #3
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    Search for motor winding varnish:

    https://www.ebay.com/itm/MOTOR-WINDI...Wx3F:rk:1:pf:0
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

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    1601

    Keep eye on ball.
    Hashim Khan

  5. #5
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    It may have been just that easy, so thanks.
    The laminations are bolted together and I had checked the top bolts. BUT, the bottom bolts were loose enough to where I got roughly a full turn on them. There are nylon washers under the heads, so I hope I didn't go too tight.
    The good news it that it is considerably quieter, but still a touch louder than the others. A funny thing - I checked the bolts on the 'quiet' one, and they were notably looser than on the noisy one.

    I have a can of Skothchkote, but the transformer is wrapped in plastic on the outside and a layer or two further in. I can only see a little bit of the top of the windings. If you guys really think it is the thing to do, I can drip some down in there.

    I take it I shouldn't have any particular concerns about safety or longevity? The Fluke says the output voltage and frequency are spot on (checked w/load), BTW.

  6. #6
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    that HF buzz like an old tv- maybe it's a switching power supply and the core is a tad misaligned- or it could be broken. If this is a two piece ferrite core held together by a spring or other means of mechanical fastening, you can sometimes give a gentle twist to the accessible part to sort of re-seat it. If it's cracked you might be able to save the day by wicking some CA into the crack- you have nothing to lose in this case anyway, unless there's a warranty that you can take advantage of. It's usually not recommended to glue the core if it comes not glued by the manufacturer, as that can change the way the core reacts to the frequencies it's working with.

    If what you have is a regular 60 hz transformer and the core is buzzing, you're safe to try pretty much any adhesive that has the potential to wick into a gap and harden there. CA would be my choice, as anything thicker would be unlikely to flow into places it might be needed. Or you can often get away with 'painting' some epoxy on the outside of the laminations.

    You could have something loose in the windings, and it's pretty much the same deal- you need to get a filler material into where it's needed, and have it harden there.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  7. #7
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    You'd want to get the varnish on the laminations, which are normally glued together with varnish that wicked-in. The varnish may glue them together well enough that they would not buzz even if the screws are loose. And the screws may not tighten them enough to eliminate the buzz.
    1601

    Keep eye on ball.
    Hashim Khan

  8. #8
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    Quote Originally Posted by PStechPaul View Post
    The transformer laminations may have loosened up. They are typically dipped in lacquer or epoxy to keep them tight. It may also be possible for grain-oriented silicon steel to lose some of its magnetic properties due to shock, which might change the inductance and thus the quiescent current. You might see differences in line current, especially viewing the waveform on a scope. Saturation due to lower inductance will probably show up as current peaks. If you have a variable transformer (Variac or Powerstat), see if the buzzing diminishes as you lower the voltage.
    I would go with this procedure. JR
    My old yahoo group. Bridgeport Mill Group

    https://groups.yahoo.com/neo/groups/...port_mill/info

  9. #9
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    These Tripplites have left me with a very bad taste. One of them was tested by unplugging it. Its raison d'Ítre is to signal that it has lost power, then cleanly (uninterrupted, right?) provide battery power for a short while allowing a proper shut down of your equipment. Nope. Simply stopped providing power instantly. Took me a day to restore the corrupted operating system, working environment, etc. Tripplite's customer support was utterly lame.

    The replacement for it is also essentially no more than a power bar - it has multiple outlets on the back, but none of them provide battery backup. The fancy screen says the battery is fine.

    These may be the most widely used brand of IPS so presumably they can't all be this bad and perhaps we just got a bad batch, but regardless I am extremely unimpressed. If you have these things, I would test them periodically in a way that does not put data at risk. And of course you always test that you are able to successfully *restore*, not merely *backup* your data.
    "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

  10. #10
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    For a long time now, I have been using laptops as my primary computers, so I have not had to worry about power outages. They typically will continue to run for several hours. Perhaps a better UPS would be a dozen 12V SLA batteries to provide 144-160 VDC to the desktop computer switching power supplies, which should be perfectly happy. Keep the batteries charged with a dozen float chargers. You can get 12V 12 A-h SLA batteries for about $25 each, and float chargers are maybe another $5, and that would be enough for 1.8 kW-hr, for a total cost of about $360. You might even be able to use a 2 kVA isolation transformer, rectifiers, and some capacitors to make a nominal 160 VDC supply for the computers, as well as keep a charge on the batteries, and use a diode to automatically switch to battery power when the mains power drops. DC power may also work for peripherals such as monitors, printers, and routers.

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