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Wall Power adapter output concern

Discussion in 'General Electronics Chat' started by Uziel, Sep 17, 2017.

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  1. Uziel

    Uziel New Member

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    Hello, this question may sound senseless but I am novice, just looking for clarification. My Cordless phone has a Wall wart AC Power Adapter rated at 9v 500mAh. As far as replacement is concerned, does output power only matters or we have to be specific with ratings also? Like a 4.5V 1A adapter output will also be 4.5W as original rating. I have read in this forum that higher current rating may not matter but higher voltage may damage. Also, I have heard that SMPS based supplies senses the actual load and outputs accordingly. Please correct me.
     
  2. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    You need to get a 9V adapter.
    You need a 500mA or larger. (I would look for 500mA to 1A) In theory a million Amps will work just fine. (if you can afford one LOL)

    Amps or Watts need to be equal to or larger.
     
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  3. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Local thrift shops have dozens of these older-style, iron core transformer wall-warts for ~$1. Do not use a modern (light-weight) switching power supply, but look for the ones that have a bit of weight when you pick them up.

    It is usually much harder to match the coaxial plug that was on the old charger than to match the voltage/amperage rating.

    Make sure that the replacement wall-wart has AC (unrectified) output; not DC (internally half or full-wave rectified)
     
  4. dave

    Dave New Member

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  5. alec_t

    alec_t Well-Known Member Most Helpful Member

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    :confused: First check markings on your existing adapter and your phone base unit to be certain whether the unit requires an AC input (which I doubt) or a DC input. Make a note, too, of the plug polarity if the unit input is DC.
     
  6. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    About one third of older consumer appliances utilized an AC wall-wart where the rectification, battery charging, and regulation is done inside the appliance; not the wall-wart. The wall-wart markings clearly show if it is AC or DC output.

    Most older DC wall-warts have either one internal rectifier (half-wave), or an internal full-wave bridge, and some have an internal filter capacitor and some dont. When used as a DC supply for projects, the DC wall-warts are usually have a big voltage drop-off between no-load and loaded, and require a chip voltage regulator inside the project. If they dont have an internal filter capacitor, or the internal one is too small, you usually have to add one externally...
     
    Last edited: Sep 18, 2017

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