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Re: Humming Isolation Transformer and DC pollution of AC lines

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  • nuno_tv
    ... condition my ... balanced output ... mentioned ... quoted: when ... greater ... because ... this ... unwanted DC ... practical ... it seems ... Hi alex,
    Message 1 of 25 , Mar 31, 2006
      --- In Electronics_101@yahoogroups.com, "Alex Calderon" <alexc@...>
      > Hi Folks,
      > I just installed a 1KVA EIT (Extreme Isolation Transformer) to
      condition my
      > AC lines for an AV system. The jumpers are configured for a
      balanced output
      > (120-0-120) which gives out 240v.
      > However, the transformer hums. There were tech write ups that
      > about the presence of DC pollution in AC power lines. As
      quoted: "when
      > there's DC on the line, we have an asymmetrical field which causes
      > vibrations. The laminations are 'pushed' together in one direction
      > of the DC."
      > My question now is -- what would be the best approach to resolve
      > problem? Can anyone recommend a filter circuit to short out the
      unwanted DC
      > from my powerlines. Would appreciate if anyone can provide a
      > schematic and a description of how it works.
      > BTW, I have already installed a MIL-grade Corcom EMI/RFI filter but
      it seems
      > that the DC problem does not occur within the EMI/RFI frequencies.
      > Alex

      Hi alex,

      To make sure it is not a mechanical "something" loose, you can
      immerse the entyre transformer into melted solid parafin. Let it in
      there until all the air bubbles get out. Remove it and let it drip
      the excess parafin until it solidifies again.

      I've used this method for many years for that same purpose. As long
      as the transformer doesn't get TOO hot (iron cores transformers don't
      get hot enough if working properly) there will never be a problem.

      Nuno T.
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