19.5V Battery power question

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  • leehljp
    Just me
    • Dec 2002
    • 8480
    • Tunica, MS
    • BT3000/3100

    19.5V Battery power question

    I have and use 3 external monitors for my laptop, two 26-28" at home and work, and recently bought a 21.5" HP monitor to take with me for an extra display when needed at individual locations. My HP has a power cord that has a power adapter that steps the voltage down to 19.5V 1.28A.

    There have been a couple of times where I have been where electricity was not available or rather did not have an extension cord long enough with me.

    Can I use a Dewalt 20V or other 19.x volt battery to run the 21.5" monitor in such cases?

    I used to just try this type of experiment without hesitating years ago, but now I prefer to ask those more in the know.
    Last edited by leehljp; 03-02-2023, 08:40 PM.
    Hank Lee

    Experience is what you get when you don't get what you wanted!
  • LCHIEN
    Internet Fact Checker
    • Dec 2002
    • 21173
    • Katy, TX, USA.
    • BT3000 vintage 1999

    #2
    It doesn't bring to mind any issues in doing so besides the issues in making connectors to hook this all up.
    But then again I am assuming that the battery pack is just a battery and that the output of your HP power adapter for the monitor is just a voltage supply.
    I suppose that the 19.5 V battery can be higher when charged. But that the Monitor will work OK with 19.5. to whatever the battery maximum is. There's usually headroom.

    But, I cannot guarantee it, so whatever you do is at your risk
    Loring in Katy, TX USA
    If your only tool is a hammer, you tend to treat all problems as if they were nails.
    BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

    Comment

    • mpc
      Senior Member
      • Feb 2005
      • 989
      • Cypress, CA, USA.
      • BT3000 orig 13amp model

      #3
      Most lithium-ion battery packs output as much as 21 volts at 100% charge... but output lower voltage as they discharge. 18 to 18.5 volts is the typical average for the bulk of the usable output. The "18650" battery cell is a very common size lithium-ion cell used in many cordless tool battery packs. Fully charged it creates about 4.2 volts; 5 cells in series generates 21 volts. But once it has discharged just a little bit, down to 90% of a full charge, the voltage has dropped to about 4.0 volts. So 5 cells = 20.0 volts. As the cell continues to discharge, the voltage drops more slowly until the cell is at only 10 to 20% charge; the voltage is about 3.6 volts... so 5 cells generates 18 volts. Your monitor will have to accept a little over-voltage initially and then a more substantial under-voltage until the battery shuts itself off. What will that do to the monitor's internal power circuits? Can't say for sure.

      Will the monitor function on that reduced voltage? Probably as most electronics these days use switching power supplies internally to step the input voltage up and down to the various voltages needed by the electronics (3.3 or 5.0 volts typically) and the panel back-or-edge-lighting. Switching power supplies have an oscillator that turns transistors ON and OFF rapidly to feed a transformer with a high frequency square-wave-ish signal, the output of that transformer is rectified back to a different DC output voltage. The transformer may have multiple output windings to generate the different output voltages or the system may use multiple independent oscillator + transformer + rectifier assemblies for each needed output voltage. Either way, varying the ON versus OFF time - the "duty cycle" - of the oscillations adjusts the output voltage... so these DC-to-DC converter style power units can handle a fairly wide range of input voltages. Many laptop power bricks, and modern PC power supplies, are rated for the range 110 to 220 volts AC input, 50 or 60 Hz, rather than being designed for just one or the other as things used to be several years ago. That's because they convert the input AC directly into a high DC voltage and then feed it to a similar DC-to-DC oscillator + transformer + rectifier assembly to generate the proper output voltage. When running on 110 AC the oscillator uses a high duty cycle, when running on 220 the duty cycle will be cut in half to provide the same net input energy to the transformer. The question becomes: how "adaptable" are the power units inside the monitor to varying input voltages? A too-low input voltage makes the oscillators work/run harder... perhaps too hard leading to their failure from overheating. There's no way to know for sure without a schematic of the monitor or other internal tech details.

      If the monitor's power brick can accept "modified sine wave" AC input, rather than the pure sine wave found in proper AC outlets, then a battery powered inverter would work. Ryobi makes a 150 watt model for $100 at the Borg... I don't know if Dewalt offers a similar gizmo but I'd bet they do. These little inverters are handy for power outages to keep the Internet router working, re-charge cell phones or some laptops, etc. Your monitor's power brick is generating about 25 watts output so, assuming less than 100% efficiency, it probably draws no more than 30 watts from the AC outlet... well within the capacity of small inverters.

      mpc

      Comment

      • leehljp
        Just me
        • Dec 2002
        • 8480
        • Tunica, MS
        • BT3000/3100

        #4
        Originally posted by mpc

        If the monitor's power brick can accept "modified sine wave" AC input, rather than the pure sine wave found in proper AC outlets, then a battery powered inverter would work. Ryobi makes a 150 watt model for $100 at the Borg... I don't know if Dewalt offers a similar gizmo but I'd bet they do. These little inverters are handy for power outages to keep the Internet router working, re-charge cell phones or some laptops, etc. Your monitor's power brick is generating about 25 watts output so, assuming less than 100% efficiency, it probably draws no more than 30 watts from the AC outlet... well within the capacity of small inverters.

        mpc
        That Ryobi (or other) inverter might work. I will look into it. I should have put a pict of the adapter in with the original post, but was involved with numerous honey-do items at the time I was posting.

        Thanks!

        Click image for larger version  Name:	19.5 V Adapter 24.96W.jpg Views:	0 Size:	119.1 KB ID:	854337
        Last edited by leehljp; 03-03-2023, 08:53 AM.
        Hank Lee

        Experience is what you get when you don't get what you wanted!

        Comment

        • LCHIEN
          Internet Fact Checker
          • Dec 2002
          • 21173
          • Katy, TX, USA.
          • BT3000 vintage 1999

          #5
          Hank, does the monitor itself have a label stating the power input requirements separate of the adapter (which is a separate piece of gear) that perhaps states the input voltage range of the monitor and its power or current needs. I'll bet it does.
          If the input range covers about 18 V to 21 or 22 volts you are probably OK.
          Loring in Katy, TX USA
          If your only tool is a hammer, you tend to treat all problems as if they were nails.
          BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

          Comment

          • leehljp
            Just me
            • Dec 2002
            • 8480
            • Tunica, MS
            • BT3000/3100

            #6
            Originally posted by LCHIEN
            Hank, does the monitor itself have a label stating the power input requirements separate of the adapter (which is a separate piece of gear) that perhaps states the input voltage range of the monitor and its power or current needs. I'll bet it does.
            If the input range covers about 18 V to 21 or 22 volts you are probably OK.
            That is/was a good idea. I turned the monitor upside down and on a narrow strip was a lot of tiny information; But after looking at it intently through my phone's viewer, it had the same criteria for input as the power adapter pict that I posted above. I think MPC's idea of the Ryobi 18V inverter to 120Vwill be the way to go and just use the power cord for the monitor.

            Thanks for the idea.
            Hank Lee

            Experience is what you get when you don't get what you wanted!

            Comment

            • dbhost
              Slow and steady
              • Apr 2008
              • 9270
              • League City, Texas
              • Ryobi BT3100

              #7
              FWIW for my camper build I am intentionally seeking a 24 inch or larger screen that will run on 12v dc...
              Please like and subscribe to my YouTube channel. Please check out and subscribe to my Workshop Blog.

              Comment


              • leehljp
                leehljp commented
                Editing a comment
                They are available, try a camper city/camper world place. They must have a 12V systems somewhere.
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