Adapters Voltages?

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  • ivtec
    Badcaps Legend
    • Dec 2008
    • 1967
    • USA

    #1

    Adapters Voltages?

    Hi guys; can you tell me what is the correct load Voltage on a Power Adapter,
    for example i have here an DC 3v 200 ma power adapter when i test it on my Fluke it reads about 7v,without load, is this bad?
    i rarely find a Power adapter that reeds the exact voltage that is in the adapter specs always have 2 to 3 volts or more more,what is too much voltage?
    Last edited by ivtec; 06-18-2015, 10:55 AM.
  • budm
    Badcaps Legend
    • Feb 2010
    • 40746
    • USA

    #2
    Re: Adapters Voltages?

    The linear non regulated power supply will show higher Voltage without the load, it should be 3V with 200mA load, without the load the output can as much as 50% higher, but in your case, your meter may have bad batteries or way out of calibration.
    Never stop learning
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    • ivtec
      Badcaps Legend
      • Dec 2008
      • 1967
      • USA

      #3
      Re: Adapters Voltages?

      Originally posted by budm
      The linear non regulated power supply will show higher Voltage without the load, it should be 3V with 200mA load, without the load the output can as much as 50% higher, but in your case, your meter may have bad batteries or way out of calibration.
      Thanks budm, but i measured with another meter and it shows same v,
      if you say without load it can be 50% more, then it's only 1 volt over .

      Comment

      • budm
        Badcaps Legend
        • Feb 2010
        • 40746
        • USA

        #4
        Re: Adapters Voltages?

        "DC 3v 200 ma power adapter when i test it on my Fluke it reads about 7v" 3V to 7V that is way more than 50%.
        3V, so 50% higher will be 4.5V, you are getting 7V.
        Never stop learning
        Basic LCD TV and Monitor troubleshooting guides.
        http://www.badcaps.net/forum/showthr...956#post305956

        Voltage Regulator (LDO) testing:
        http://www.badcaps.net/forum/showthr...999#post300999

        Inverter testing using old CFL:
        http://www.badcaps.net/forum/showthr...er+testing+cfl

        Tear down pictures : Hit the ">" Show Albums and stories" on the left side
        http://s807.photobucket.com/user/budm/library/

        TV Factory reset codes listing:
        http://www.badcaps.net/forum/showthread.php?t=24809

        Comment

        • pc7fan
          Badcaps Veteran
          • Aug 2013
          • 52
          • Canada

          #5
          Re: Adapters Voltages?

          Once I had a 12V 500mA wall wart and unloaded it was reading around 28V (but with a 24 ohm resistor - 500 mA load), it was ±10% of the labeled 12 volt rating.

          Comment

          • budm
            Badcaps Legend
            • Feb 2010
            • 40746
            • USA

            #6
            Re: Adapters Voltages?

            Originally posted by pc7fan
            Once I had a 12V 500mA wall wart and unloaded it was reading around 28V (but with a 24 ohm resistor - 500 mA load), it was ±10% of the labeled 12 volt rating.
            If that is the case I hope it has 50VDC rating caps in that wall wart.
            To get 28V the cap is charged up to the peak of the transformer Voltage, so in this case the transformer AC is around 28V *0.707 = 19.796V!
            Never stop learning
            Basic LCD TV and Monitor troubleshooting guides.
            http://www.badcaps.net/forum/showthr...956#post305956

            Voltage Regulator (LDO) testing:
            http://www.badcaps.net/forum/showthr...999#post300999

            Inverter testing using old CFL:
            http://www.badcaps.net/forum/showthr...er+testing+cfl

            Tear down pictures : Hit the ">" Show Albums and stories" on the left side
            http://s807.photobucket.com/user/budm/library/

            TV Factory reset codes listing:
            http://www.badcaps.net/forum/showthread.php?t=24809

            Comment

            • Behemot
              Badcaps Legend
              • Dec 2009
              • 4845
              • CZ

              #7
              Re: Adapters Voltages?

              That is pretty normal situation for wall transformers and usually the smaller the transistor, the higher the no-load voltage which than drops drastically with load. Not sure where you took that 50 % from, that is no general rule…often it is that way, often not.
              Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

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              • budm
                Badcaps Legend
                • Feb 2010
                • 40746
                • USA

                #8
                Re: Adapters Voltages?

                "the higher the no-load voltage which than drops drastically with load. Not sure where you took that 50 % from" from taking apart 100's of 100's of wall warts for failure analysis, beside if they design the wall wart with such high output impedance they will have to use higher Voltage cap rating.
                Also if the device being power by this wall wart and only drawing 80% of rated current for head room purpose, the supply Voltage will be way too high for the device.

                "Once I had a 12V 500mA wall wart and unloaded it was reading around 28V (but with a 24 ohm resistor - 500 mA load), it was ±10% of the labeled 12 volt rating." Just think about this, what Voltage will be feeding the device if it is only drawing 100mA or less in standby mode? Will you want to use this wall wart?
                Last edited by budm; 06-19-2015, 09:45 AM.
                Never stop learning
                Basic LCD TV and Monitor troubleshooting guides.
                http://www.badcaps.net/forum/showthr...956#post305956

                Voltage Regulator (LDO) testing:
                http://www.badcaps.net/forum/showthr...999#post300999

                Inverter testing using old CFL:
                http://www.badcaps.net/forum/showthr...er+testing+cfl

                Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                http://s807.photobucket.com/user/budm/library/

                TV Factory reset codes listing:
                http://www.badcaps.net/forum/showthread.php?t=24809

                Comment

                • Behemot
                  Badcaps Legend
                  • Dec 2009
                  • 4845
                  • CZ

                  #9
                  Re: Adapters Voltages?

                  Most devices have DC-DC inside today and for battery chargers, it is actually intention as the voltage slowly rises above nominal (charged batteries always have more than nominal).

                  BTW I am talking about 50/60Hz transformers, are we on the same subject here?
                  Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

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                  • budm
                    Badcaps Legend
                    • Feb 2010
                    • 40746
                    • USA

                    #10
                    Re: Adapters Voltages?

                    "BTW I am talking about 50/60Hz transformers, are we on the same subject here?" Yep, simple linear power supply with iron core transformers, with simple bridge and filter cap, not regulated output.
                    28V no load and 12V full load, that is the worst transformer regulation factor I have ever heard of, no load of 1.8 factor (no load is 80% higher than full load) spec is about the worst I ever run into.
                    http://carroll-meynell.com/technical-transformer
                    Last edited by budm; 06-19-2015, 01:10 PM.
                    Never stop learning
                    Basic LCD TV and Monitor troubleshooting guides.
                    http://www.badcaps.net/forum/showthr...956#post305956

                    Voltage Regulator (LDO) testing:
                    http://www.badcaps.net/forum/showthr...999#post300999

                    Inverter testing using old CFL:
                    http://www.badcaps.net/forum/showthr...er+testing+cfl

                    Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                    http://s807.photobucket.com/user/budm/library/

                    TV Factory reset codes listing:
                    http://www.badcaps.net/forum/showthread.php?t=24809

                    Comment

                    • Behemot
                      Badcaps Legend
                      • Dec 2009
                      • 4845
                      • CZ

                      #11
                      Re: Adapters Voltages?

                      Small 3-5V ones often have 6-9 V…
                      Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

                      Exclusive caps, meters and more!
                      Hardware Insights - power supply reviews and more!

                      Comment

                      • budm
                        Badcaps Legend
                        • Feb 2010
                        • 40746
                        • USA

                        #12
                        Re: Adapters Voltages?

                        Worst case factor of 1.8:
                        3V * 1.8 = 5.4V
                        5V * 1.8 = 9V

                        12V:28V = 2.33 factor, very bad transformer.
                        Last edited by budm; 06-19-2015, 02:29 PM.
                        Never stop learning
                        Basic LCD TV and Monitor troubleshooting guides.
                        http://www.badcaps.net/forum/showthr...956#post305956

                        Voltage Regulator (LDO) testing:
                        http://www.badcaps.net/forum/showthr...999#post300999

                        Inverter testing using old CFL:
                        http://www.badcaps.net/forum/showthr...er+testing+cfl

                        Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                        http://s807.photobucket.com/user/budm/library/

                        TV Factory reset codes listing:
                        http://www.badcaps.net/forum/showthread.php?t=24809

                        Comment

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