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AC Adapter question

Discussion in 'Electronic Repair' started by [email protected], Feb 2, 2006.

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  1. Guest

    The AC adapter with my computer speakers is broken/dead and I want to
    replace it with a new one. The specifications on the dead adapter are
    as follows.

    INPUT: 120VAC 60Hz
    OUTPUT : 13VAC 800mA

    If I have to replace it with a new one what are my options. Should I
    look for exactly the same specifications or something other will also
    work? Do I have to replace it with an AC to AC adapter or can I replace
    it with a DC adapter? If I can use a AC to DC adapter what
    specifications should I remember.

    thankyou very much in advance.

    Naveen
     
  2. Answered elsewhere. Just get a direct replacement.

    Kal
     
  3. Cyrus®

    Cyrus® Guest

    As long as the plug size new adaptor is matches with dead adaptor , 9VAC
    900mA, 10VAC1000mA,12VAC950ma will do the job.<< AC OUTPUT not DC >>

    Best Wishes
    Cyrus®
     
  4. You can substitute a DC adaptor for an AC one, but not the other way
    around.
     
  5. Gerard Bok

    Gerard Bok Guest

    No. You cannot!
    (Only in rather rare situations this is possible.)
     
  6. James Sweet

    James Sweet Guest


    The old 8 bit Nintendo comes to mind, the original adapter was AC but DC
    worked fine as it had a rectifier and regulator in it. Many things that
    use AC output adapters do so for a reason though and will not work
    correctly on DC, though it's unlikely to cause damage right away.
     
  7. Please explain why not.
     
  8. Gerard Bok

    Gerard Bok Guest

    Well, at first: if DC adapters were for 'universal use' no one
    would bother to design / produce / stock / sell AC types :)

    If you supply AC to a device, you can do all sorts of nice things
    with the input power:
    - rectify it
    - rectify it with a doubler (giving + and - for the same voltage)
    - rectify it and pull some mains frequency for timing. (Old times
    clocks used to do that. Before crystals and digital deviders
    became cheap.)
    - some loads do not allow dc at all. As several switches don't.
    Some motors don't either. In general: if the device is some kind
    of coil, don't even think of replacing an AC adapter with a DC
    type.

    What also counts is the voltage. If an adapter is labeled 10 Volt
    AC it is quite easy to pull some 14 volts out of it. (Rectify it,
    which yields root 2 times the ac voltage.) You cannot do the same
    with DC. (And you cannot replace a 10 volt AC type by a 14 volt
    DC type either. :)
    (Please note, that also the load applied may play a rather
    important role in the actual voltage an adapter supplies!)

    James Sweet mentioned a special case: if the only thing done on
    the input is a rectifier, you can connect a DC adapter.
    That is: if the device is designed to handle a rather big range
    of input voltages and if the rectifier is overdesigned, as in the
    DC situation the current through half the rectifier is more than
    double that of the AC situation. (Again: with cheap diodes
    plentiful in supply, a modern device is likely to handle this
    situation. Old devices maybe not. I've seen many 1N4148 'bridge
    rectifiers :)
     
  9. Err, AC wallwarts are cheaper and because of slightly smaller size like
    for like may be the answer for some. And of course AC is fine for things
    like low voltage lighting. Might also be that a device produced for using
    throughout the world makes sense to have the DC conversion and regulation
    within it.
    I think you're clutching at straws. ;-)
    It would be a very poor description and specification of transformer which
    supplied 14 volts while being labelled as 10 volts. ;-)
    You're missing the point that most electronic devices which use an AC
    wallwart will have internal regulation. And the only common one is most
    external modems. Why - I've got no idea.
    With any DC device designed to be fed with an AC source you can feed it
    with DC - provided you take into account the voltage drop through the
    rectifier. And given the poor regulation of most AC wallwarts this is
    rather easy to calculate.
     
  10. James Sweet

    James Sweet Guest


    That's really not always true, I had an external modem years ago that
    would only work properly from an AC output adapter, and a couple
    different bubble lamp things and kinetic sculptures that used
    synchronous motors and vibrating air pumps, those devices all required
    12VAC and would not work correctly from DC. I've built a few digital
    clocks that also require an AC output wall wart because they derive the
    timing from the line which is much more accurate long term than a
    crystal though since those are not a commercial product I can't really
    count them.
     
  11. Yes, but they're not true DC devices if they include an AC motor etc. The
    modem should have worked properly - I've used a DC supply for one with
    success. But if say its internal electronics have a 12 volt rail the DC
    supply will need to be higher for the internal regulator to work, and
    regulators fed with a lower voltage than they require can output nasties.
    Yes again, but then it's not a DC device. The OP's speakers will be.
     
  12. What also counts is the voltage. If an adapter is labeled 10 Volt
    Many of these shitty supplies are marked with RMS voltage.
    The PEAK voltage however is RMS X 1.414 (X2 for full wave) which
    is what appears after being rectified and smoothed. Best to check (if
    possible)
    the output from the original with a 'scope or meter (a meter measures
    RMS)
    or better still get a direct replacement.
     
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