Please Help Out!

Discussion in 'General Electronics Chat' started by spiros0310, Mar 3, 2007.

  1. spiros0310

    Thread Starter New Member

    Mar 3, 2007
    I Recently Bought A New Digital Multimeter. I Tested It On A 1.5 V Battery And It Returned A Voltage Of 1.46. That's Ok, But When I Tested It On An Ac To Dc Adaptor (the One I Use To Recharge My Cellphone) Which Outputs 4.5 V Dc, It Returned Something Like 7 Or 8 Volts. The Same Thing Happened With Other Adaptors Of Different Output Voltages. What Am I Doing Wrong? I Have Set The Multimeter To The Appropriate Scale (20 V) And The Probes Are In The Correct Places. I Even Used A Resistor So As Not To Burn The Multimeter's Fuse. Please Help -- If You Can!
  2. hgmjr


    Jan 28, 2005
    I imagine what you are measuring is the unloaded voltage output from the adaptors. Some adaptors need to be loaded to produce the rated voltage.

  3. beenthere

    Retired Moderator

    Apr 20, 2004
    Hqmjr is correct about the wall adaptor's poor regulation. Many only get to within 10% of the stated output voltage when the load is almost correct.

    Measuring voltage involves a very high resistance in the meter's input circuit. There is no need to use a series resistor to keep the fuse from blowing. The meter's fuse protects the internal circuitry while it measures current.
  4. mrmeval

    Distinguished Member

    Jun 30, 2006
    You'd need to measure that under load. That is hard to do. You could find a 6V lamp and use that or calculate 75% of the current it's rated for then calculate the resistor and wattage you'd need to put across it. Then measure.