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wall wart question

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  • #16
    My daughter's tablet, if connected to a normal micro usb connector, will run normal even if it's battery is low but won't charge. For this it needs the original charger that has a dual voltage output (5/18V). When you connect it, I suppose, the tablet "negotiates" the correct voltage and gets it from the charger.
    Mini usb plugs have 5 contacts, one with a resistor that informs the device of the available current. I had to build a special cable with a 18Kohm resistor in the plug to be able to charge my Garmin GPS from a 5v 1000mA generic charger. (this is the required current for the device)
    Helder Ferreira
    Setubal, Portugal


    • #17
      The difference between "maintaining" and "charging" from USB is very likely determined by the capacity of the USB.... Some are older and have a much lower current limit. Newer ones seem to have higher limits, ever-increasing as time goes on.... and devices get more power-hungry.

      The charger cannot pull more than is available.

      As for the charge rate etc vs "capability".... A 120V (or 230V) outlet can run a reasonably powerful machine.... but it can also operate a low power pilot light.... The power draw is determined by the load. A 40W bulb or a 150W bulb plug in the same place, and draw according to their resistance, NOT the capability of the outlet.
      CNC machines only go through the motions


      • #18
        I have a Nikon digial camera that uses a USB cable to transfer data and charge the battery. If it is plugged into a standard USB socket it won't charge unless you "tell" the camera this is happening. If you plug the cable into the Nikon wall plug charging adapter it charges fine.


        • #19
          I think computer USB ports are rated at 500 mA. My guess is the camera either knows it's a data connection and doesn't bother charging or sees the USB power supply as underrated (not sure of charging capacity of camera charger) and deems it insufficient to charge, thus turning off the charging circuit.


          • #20
            Originally posted by danlb View Post
            A reply for Boomer and Magpie...

            Boomer, when you plug the 12 volt, .4 amp charger into the shaver that is designed for 2.3 volt at .1 amp it is providing a huge power surge. If there is a diode bridge it will allow a .4 amp surge at 12 volts to charge the battery quickly. This will drastically decrease the lifespan of the battery.


            Dan --- that's what's weird - the shaver is the 12 volt,,, this is something that does not make any sense at all to me and yet it's happened quite a few times...

            im plugging the beard trimmer's 2.3 volt charger into the shavers 12 volt receptacle, so not only is it way lower voltage - the polarity is also reversed,,, the charge led's on the shaver then totally freak out for a split second then all the sudden settle way higher off the last red increment that it was displaying a split second before,,, about half way charged, the shaver then acts normal and lasts for days and the green increment scale gradually goes down to the red again before it gets too low and needs another charge... I never repeated the process twice in a row to see what would happen as I was just glad I did not blow up my shaver.

            I have no explanation except maybe it "shocks" the battery and does something to it to get more residual power that it was holding in it, or maybe there's a reserve cap that it triggers or something... ?


            • #21
              In the name of electronics science I have an update, went to shave this morning and as luck would have it the shaver needed a charge - it was on the last increment which is red,

              you know how I stated the norelco plug fit's like a glove? it doesn't -- but it does connect, if you look at the pics of the plugs it's the one with the connectors right at the edge of the plugs end,,,

              so - I did this AFTER drinking my morning coffee and took notes, the norelco plug actually connects in both directions I think due to the leads almost hanging out of the end of it,,, but it will not physically go in fully either way, nothing seems to happen in the normal direction with the center groove cut out on one side aligned with the male piece in the shaver (which would put the polarity in reverse)

              yet when I went to put it in the opposite direction the led's on the shaver all lit up, this was just a split second,,,

              I then quickly disconnected and there it is plain as day the shaver it not half charged - it's instantly fully charged.

              this is a 2.3v 100ma charger being hooked up to the 12v 400ma shaver and it is in the correct polarity as the plugs are reversed yet I was hooking it up backwards so the polarity is the same...

              go figure,,,

              then I plug the remingtons charger into the remingtons shaver and it shows full charge but the last green increment is blinking - which means almost fully charged...

              Edit; I stated I heard a strange sound in my first post but did not hear anything this time,,, I may have equated the visual of the lights doing different things and remembered it differently - it was going off of memory of being half awake,,,

              this time it's different as I was fully awake and took notes... does anyone have an explanation?
              Last edited by A.K. Boomer; 08-08-2014, 10:14 AM.


              • #22
                I'm not intimately familiar with appliance chargers but I think I may understand what is happening. First, would it be possible to take two small wires strands (thin paperclips would be ideal but may be too thick) and stick these in the charger when it is connected to the shaver. Use a multimeter to check the output voltage. Also check the voltage with the charger disconnected from the shaver. All electrical generating devices have a higher open circuit voltage than the nominal output voltage. Imagine an auto battery charger running but disconnected from a battery. It will probably put out 14 volts. Connect it to the battery and the indicated voltage drops. Depending on the circuit inside the 2.3V charger, the OCV could be 12 volts. This charger may depend more on the appropriate shaver's charging circuit to regulate the inrush so the OCV doesn't damage the shaver. The 12V shaver probably has a lower impedance thus allowing the 2.3V charger to deliver the OCV for some amount of time longer than it would with the 2.3V shaver. I know this doesn't explain what the 2.3V charger does differently than the 12V charger, but it may be a start.

                If I'm completely blowing smoke, someone please correct me.


                • #23
                  I quit shaving about 11 years ago, just trim once a month and life has been much better since.

                  Boomer, paint the end of one cord, and the socket on the matching device.