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2 connections to one solar panel

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  • 2 connections to one solar panel

    What happen if i connect two things to one solar panel?
    for example: A 20Wp i connect the cable to a small 5watt pump and also to a step down usb module (input 6-30v output 5v) to charge a powerbank. In this setup i dont use a chargecontroller.

    will the pump work and will the powerbank be charged during peakhours?

  • #2
    No. Next question.
    MSEE, PE

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    • #3
      Unfortunately a without a constant voltage from say a battery a 20watt solar panel will probably not run both a 5 watt pump & a 5v USB charger.

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      • #4
        This works. 15wp 17.2v panel to usb stepdown 2 outputs 5v, one to powerbank the other with stepup to 4v powersupply input 6.2v. Also i can run a usb (hydroponic) pump
        Attached Files
        Last edited by fivewin; 04-23-2017, 03:48 AM.

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        • #5
          Here again the pict
          Attached Files

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          • #6
            Originally posted by fivewin View Post
            This works. 15wp 17.2v panel to usb stepdown 2 outputs 5v, one to powerbank the other with stepup to 4v powersupply input 6.2v. Also i can run a usb (hydroponic) pump
            Sure that might work if the sun is high in the sky and there are no clouds but even small shadows will shut down any output from the panel to your loads. If that process is ok with you then have fun with it.

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            • #7
              Originally posted by fivewin View Post
              This works. 15wp 17.2v panel to usb stepdown 2 outputs 5v, one to powerbank the other with stepup to 4v powersupply input 6.2v. Also i can run a usb (hydroponic) pump
              Your application is not really what I would call connecting two devices to one panel. You are powering two devices by connecting them to a third device which has the sole connection to the panel.

              The biggest source of problems in connecting two devices directly to a single panel is that each one will have its own effect on the output voltage/current operating point of the panel, and that could cause problems.
              In particular if two MPPT inputs are connected to one panel, each one will try to get more current for itself by "stealing" current from the other. The result will at best be instability of the panel voltage.
              SunnyBoy 3000 US, 18 BP Solar 175B panels.

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              • #8
                Its indeed connecting devices to one panel with a module. Its not true that when its cloudy both outputs will shut down but only one. In many villages in the country where i am there are frequent power outages sometimes for days. It seems that many people find charging handphones more important than lighting. I thought this is the most simple and cheapest way for them, 12v panel as from 5 to 15Wp. From rainbarrels to bathroom ive tested a usb pump, 7liter pm 8meter distance vertically. Better some water inside by pumping rather than carrying yourself with buckets in case of poweroutage

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                • #9
                  Originally posted by fivewin View Post
                  Its indeed connecting devices to one panel with a module. Its not true that when its cloudy both outputs will shut down but only one. In many villages in the country where i am there are frequent power outages sometimes for days. It seems that many people find charging handphones more important than lighting. I thought this is the most simple and cheapest way for them, 12v panel as from 5 to 15Wp. From rainbarrels to bathroom ive tested a usb pump, 7liter pm 8meter distance vertically. Better some water inside by pumping rather than carrying yourself with buckets in case of poweroutage
                  Even on cloudy days some types of panels (poly or thin film cell) will still produce a very small amount of current. It might be that the one load that is still working is both low voltage and low current draw which allows it to keep working at some % of full output.

                  If that is enough power to keep the cell phone charged then you might have a working project. But IMO the chance of duplicating that solar power generator to work the same for everyone at all times would be shear luck. I wouldn't jump in and invest a lot of money building those systems unless you are ready for nasty customer feedback when the equipment won't always power their phones.

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                  • #10
                    You might have a point if the panel is i think less than 10wp. Till now the 15Wp is working fine charging daily the powersupply with buildin 4v battery AND a powerbank or handphone using that stepdown module with 2usb outputs. The current is ofcourse low when its cloudy.

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                    • #11
                      Originally posted by fivewin View Post
                      You might have a point if the panel is i think less than 10wp. Till now the 15Wp is working fine charging daily the powersupply with buildin 4v battery AND a powerbank or handphone using that stepdown module with 2usb outputs. The current is ofcourse low when its cloudy.
                      If you think about it a large wattage panel will just become a trickle charger when there is very little sun. Which is why starting with a small (10w) panel turns into something smaller than 5w without the full sun.

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                      • #12
                        The above "powersupply" is in fact a package with 3wp solar panel + 2 led bulbs. I use it also for a small room already 2 years now and it never happend that the battery is not been charged. Daily use of the lamp of approx 2-4 hours. Till now no problem at all with only 3wp 6-7v panel ?
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