Wall Wart Outputs

Discussion in 'The Projects Forum' started by djsfantasi, Feb 28, 2016.

  1. djsfantasi

    Thread Starter AAC Fanatic!

    Apr 11, 2010
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    I have a wall wart, whose output is rated 9VDC @ 500mA.
    I am measuring 13.7 VDC unloaded. I put a 10k resistor across the output, expecting to see the voltage stabilize. It did - to 13.7 VDC. What am I doing wrong?
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  2. Lestraveled

    Well-Known Member

    May 19, 2014
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    You are not doing anything wrong. You take a 500 ma wall wart and load it at 1.4 ma. (.3% of rated current) and get very little change in voltage. That is what should happen. Try 50% of rated and see what happens.
     
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  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That must be one of the older linear W.W.'s which rely on the rated current to bring the voltage down, the vast majority now are SMPS and output a constant voltage level.
    Max.
     
    Last edited: Feb 29, 2016
  4. djsfantasi

    Thread Starter AAC Fanatic!

    Apr 11, 2010
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    Thanks guys. Good to know, especially since the planned load is around 100mA. I guess I need a different wall wart.
     
  5. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Or you can add an LM7809 and two or three caps on the 12.7V output and run your project just fine.
     
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