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ACShielded Xformer Mystery Wire

Discussion in 'Electronic Components' started by [email protected], Apr 7, 2007.

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  1. Guest

    Hi all,

    I found a few lower power shielded transformers at a flea market, and
    they do 120 to 40 CT VAC, so perfect for small bipolar power
    supplies.. They're steel-shelled with 4 mounting screws on the bottom
    and the transformer is potted into the shell, so I can't get a look at
    it without destroying it.

    There's 6 wires coming out of it, the 5 identified and a mysterious
    grey one which is insulated from all the others ( inf. ohms) but reads
    5 different voltages ranging from 2.8 - 65 VAC when measured against
    each of the other ones. This one and all the others are insulatd from
    the case, so its not a case ground wire.

    So:

    1. Could this wire connect to an internal shield to minimize
    capacitive coupling or is it something else?

    2. If the shield, are these voltage readings normal for such a
    connection?

    3. If the shield, should I connect this wire directly to AC earth
    ground, or to chassis ground?

    I'll just ignore it if I can't figure it out, but if it is some kind
    of shielding it would be nice to take advantage of it properly.

    Thanks for any help.
     
  2. Eeyore

    Eeyore Guest

    That appears to be the case.

    Normalish I expect. There'll be some capacitive coupling.

    Both ideally.

    Connect it to ground.

    Graham
     
  3. Sometimes it is just another winding with one end unconnected and is a
    shield. Ground it.
     
  4. Salmon Egg

    Salmon Egg Guest

    If it is an electrostatic shield, the coupling would be electrostatic. You
    do not say how you measured the voltage. My guess is that you used a
    relatively high impedance meter. 100pF will have a reactance in the
    neighborhood of 25Mohm. With that, I would expect considerable voltage
    readings. Put about 100kohm in parallel with your meter to see if that
    changes your reading.

    Bill
    -- Fermez le Bush--about two years to go.
     
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