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AC to DC Transformer

Discussion in 'Electronic Basics' started by CMM, Jan 4, 2006.

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  1. CMM

    CMM Guest

    I have a car audio device (Jensen Sirius satellite receiver) that I
    want to use inside. I have an extra antenna so that's no problem. It
    has an FM modulator allowing me to tune it in on my desktop radio so
    that's taken care of too.

    The problem I have is that I need the correct AC to DC transformer.
    After testing several with 12 volt outputs, I found one that worked.
    The others either would not allow the unit to power on or would allow
    it to power on but it would immediately freeze. The transformer that
    worked has an output of 12VDC, 500mA. It worked for about half an hour
    before burning out, leading me to conclude that it isn't rated for
    this application.

    I'm not sure exactly what I need. When it comes to electronics, I'm
    somewhat ignorant. (For instance, I don't understand why only one of
    about five 12 volt transformers worked.) To select a transformer
    that's appropriate, what do I need to look for? I'm thinking the
    voltage would need to be 12. To keep the transformer from frying, do I
    need something with a higher amp rating? What's the difference between
    regulated output, max output, and constant output?

    Here are some that I'm looking at but have no idea which one (if any
    of these) would be best:

    Any information is greatly appreciated.

    -- Christian
  2. The best strategy in such a case is to use a variable regulated power
    supply and turn up the voltage until the device works as it should.

    You don't have such a supply, but you can try higher and higher
    voltages until it works. You already did some testing like this and it
    is obvious that you need a bigger power supply, probably 12 Volt, but
    you may need more to get it to work.

    Get a bigger 12 DC output supply and try it. One that can handle the
    current without melting. Hopefully that will solve the problem. It
    should have the max current written on it, but the weight of the supply
    is a good indicator too, of the current capacity, you simply need a
    bigger, heavier 12 volt DC supply.

    If the machine still doesn't work you need to try a slightly higher
    The device may be made for 15 volt and at 12 volt it just lits up but
    doesn't work properly.

    You do not know if the device needs well regulated voltage or if it can
    take raw rectified Voltage. If the device is very valuable you might
    want to consider buying a regulated supply, and maybe with variable
    voltage too, but that is expensive.
    Most devices with external power supply are fairly tolerant when it
    comes to voltage. A few volts too much is no problem. But, on the other
    hand, your device may be an exception.
  3. Pooh Bear

    Pooh Bear Guest

    Yes. Try looking on the satellite receiver to see if it mentions a figure.
    Regulated means the output voltage is constant regardless of the current ( amps ) taken by the load. This is what you
    Probably the maximum intermittent rated load.
    The long term continuous rating. You need it to be > 500mA it seems.

  4. UFO Joe

    UFO Joe Guest

    I'm an amateur, but I've been around some car audio equipment and I do not
    think that
    a 12 volt supply at 1/2 an amp is enough to drive a car audio system. 12
    volts x 0.5 amp
    only yields 6 watts of power for both the radio/tape/cd circuit and the
    speakers, right?

    No wonder the supply burned up.
  5. Pooh Bear

    Pooh Bear Guest

    Well... he said it was a receiver not a 'system' but it's unclear what that
    means. In UK parlance a receiver means just that - no amplifier - US usage
    includes an audio amplifier.


  6. Actually, it is called a tuner if it has no power amp in the US. Its
    a receiver if it has a power amp, so you use a tuner & power amp, or a
    receiver. Some marketing types don't seem to understand this. They
    think that a headphone jack on a tuner makes it a receiver.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  7. CMM

    CMM Guest

    In that case, it would be a tuner, instead of a receiver (which is
    what I had originally called it). It just grabs the satellite signal
    and then sends it back out through an FM modulator. There is not amp
    or speakers. But, it does have a large lighted display which probably
    helps account for the extra power it's pulling.

    -- Christian
  8. CMM

    CMM Guest

    It doesn't say anything but DC 12V. I'm guessing since it's intended
    to be plugged into a car's cigarette lighter receptacle, that's why it
    isn't more specific.


    -- Christian
  9. CMM

    CMM Guest

    I appreciate the feedback from everyone. With this info, I'm sure I'll
    find what I'm looking for and be up and running soon.


    -- Christian
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