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dirt cheap power transformer

Discussion in 'Electronic Design' started by PDRUNEN, Jul 2, 2004.

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    PDRUNEN Guest

    Hi Group,

    I am looking for a dirt cheap 60Hz power transfomer (or audio type) to couple a
    60Hz signal with isolation over to my electronics which is on the low side.

    I am terminating the transformer into a opamp and not using it to power any of
    the devices.

    I see that teleco 600:600 isolation transformers are also any option but they
    appear to be expensive.

    The signal I am interested in is more of a full-wave recified AC signal with
    amplitude of one volt or less. I want to be able to pass a "copy" of this
    signal over to my lowside electronics. I am interested in the peak of the
    sine, I don't care if the reproduction is exact as long as it is the same.


  2. Robert Baer

    Robert Baer Guest

    Firstly, you say nothing about voltage standoff and/or leakage
    requirements, and nothing about input/output signal levels on the xfmr.
    In any event, you are incorrect concerning the 600:600 telco xfmrs;
    they can be had for a few dollars.
    Go to a surplus store and get some small 5 or 10 watt filament
    transformers and use them.

  3. If the signal is rectified, then it is NOT a 60Hz signal any more; it
    contains harmonics up to the bandwidth of the rectifying device (possibly
    megahertz). If you pass it through a power transformer, you will lose much
    of that high-frequency response, and your wave will start looking more like
    an unrectified sine wave again.

    Also, your rectified signal contains a DC component (that is, the average
    value is not 0, unlike the original sine wave); the transformer will filter
    out that DC component, so on the secondary side the average value will be 0.

    Bottom line is that a power transformer (or any transformer) will NOT give
    you an accurate rendition of the input in this situation.

    What kind of accuracy do you need?
  4. Tweetldee

    Tweetldee Guest

    A cheap source for 600:600 audio transformers is in old modems. Go to a
    computer store and ask them if they have any old modems that they are going
    to throw away. You can probably pick up a handful for a few bucks, and have
    enough transformers to let you experiment till the cows come home.

    Dave M
    MasonDG44 at comcast dot net (Just subsitute the appropriate characters in
    the address)

    Never take a laxative and a sleeping pill at the same time!!
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