transformer voltages read too high

Discussion in 'General Electronics Chat' started by Don23, Feb 24, 2013.

  1. Don23

    Thread Starter New Member

    Feb 22, 2011
    My volt meter, ($25 Vellemann) persistently shows output DC voltages from transformers as TOO HIGH as compared with the nominal output voltage posted on the side of the various transformers. I have a whole box of 5, 9, 12, 14v transformers and they all show the same 50% (approx.) too high reading then expected. A 5v output shows 8v. A 12v might show 18v, etc. I use the transformers successfully on appliances and nothing blows up, so I'm assuming it's the voltmeter that's at fault. But when I use the same voltmeter on D, C, AA, AAA batteries the meter shows the expected voltages. Also I have a voltage regulator "chip" that outputs 5v and the volt meter shows 5 volts DC output exactly. So the misreading seems specific to transformers. Can anyone explain this? By the way, there are fresh batteries in the voltmeter.
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    The voltage marked on a transformer is the voltage at the rated load, and in my experience it is still on the generous side.

    So it should read high. Very high at no load (as it is for the measurement as you are taking it).
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  3. tubeguy

    Well-Known Member

    Nov 3, 2012
    Assuming these are wall-wort's, it's normal for them to read at higher the rated voltage with no load applied.
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