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Easy question about AC adaptor/battery

Discussion in 'General Electronics' started by Chang, Oct 1, 2003.

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  1. Chang

    Chang Guest

    As the rectifier is inside you don't have to care about the pins at
    the plug. (And don't have to open it to search for the regulator which
    is not present in all speakers). A 12V (13.8V) accumulator should work
    fine. Capacity should be 1Ah per operating hour (worst case).
  2. Tim

    Tim Guest

    When you go to tie in the battery source of power, consider adding a
    switch to select between either the rectified power from the AC/DC
    converter or battery power.
    Alternately you can add two rectifying diodes that can handle the
    current, ex. a 1N4001 diode. The rectifying diodes only allow current
    flow in one direction. So without needing to throw a switch, power to
    the speakers can come from the AC/DC or batteries. In this
    configuration, the pair of diodes are referred to as ORing diodes.

    If a switching method similar to one of the two mentioned above is not
    done, there is risk of damaging the output of the existing AC/DC
    rectifier *if* the rectification is done with a 3-terminal voltage
    regulator such as the LM338. The LM338 has a low output impedance
    (resistance). Current from the battery would flow to the speakers and
    into the output of the LM338 and potentially damage the part.

    Take a look and see if there is a 3-terminal device or just a resistor
    and zener diode used for the rectifying. If it's just a resistor and
    zener, then you'll just end up wasting a portion of the battery energy
    in the zener.

    Hopefully you can see better what I am talking about with the text
    diagram "drawn" below. Anode-Cathode shows the connections of the
    positive and negative sides of the diodes.

    AC power-->AC/DC rectifier-->Anode-Cathode--\
    / (if any)
    Battery power--------------->Anode-Cathode--/

    Adding an switch or pair of rectifier diodes would require cutting the
    existing connection between the AC/DC rectifier and the
  3. N. Thornton

    N. Thornton Guest

    have a set of PC speakers that have an AC adaptor for power. It is
    Its a simple question. The simple answer is you'll want a 12v battery,
    or 8x D cells in series. And a plug to fit into your speaker power

    Regards, NT
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