Announcement

Collapse
No announcement yet.

My panels at night

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • My panels at night

    I intend to add in parallel 25vdc 30a external to my 21.8v 1400w panel source, to charge my batteries of 12v 600ah, for in the night there is no sunlight.
    Will the external power disturb the panels? At night since there is no sunlight, do panel dissipate batteries power at night, because I measured the resistance of the panel in the night and in absolute darkness and saw about 70 Ohms.
    Any advice thanks!

  • #2
    Your Solar Charge Controller ( you are using a controller right ? ) provides the isolation to prevent the PV panels from being backfed by battery at night, If you are connecting another charging source, be sure it never exceeds the voltage the Charge Controller would be expected to provide.
    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister

    Comment


    • #3
      Do you have a charge controller of any kind? Those voltages are a bit high for charging a 12v battery.

      Also, what do you mean by a 25vdc 30a external? External what? AC source inverter?

      To answer your question about the back current (current flowing backwards through the panels), all panels have diodes that prevent current from traveling the wrong way through them. You can see the difference if you switch the leads on your multimeter (red wire to negative, black to positive). Should be in the megaOhms.

      Comment


      • bcroe
        bcroe commented
        Editing a comment
        The diodes all panels have are bypass diodes, to help deal with partial shading. They are
        not capable of preventing current flowing backwards through the panels, but your controller
        should cover that need.

        The resistance of a panel isn't very meaningful, taken with a 3V source. Not being linear
        (and also dependent on temperature and light), entirely different behavior can be expected
        at other voltages and conditions. A different reading with reversed meter leads is a hint.
        Bruce Roe

      • Diceman83
        Diceman83 commented
        Editing a comment
        Ah, my mistake. Thanks for the clarification!

    • #4
      Tnx Mike and Diceman,
      I made my controller using 3205s and 358 comparator, the controller works fine because it never exceeds the rated voltage, I never care about current since it never reaches what I rated it. My controller has bypass diode against polarity but can't see any no return valve (diode). The resistance of my panels in absolute darkness is 70 Ohms, by Ohms law, means there's a discharge. If I use a blocking diode as no return, I'll suffer some losses.
      (25vdc 30a external), i mean a rectified mains through a transformer capable of delivery of 30amps @ 25v approximately. I appreciate your comments.

      Comment


      • #5
        Iam sorry I mean to say my panels have a bypass diode not controller pls.

        Comment


        • #6
          I am hinted, and helped Bcroe!
          Can i permanently parallel the connections of the panel to other dc source of the same magnitude (voltage) as the panel in to my controller since it is designed to withstand 60vdc input? Is there no stress on the panels or do I need to make use of another controller for the other source? Or any advice!

          Comment


          • #7
            PV panels can't be connected directly in parallel with a power supply. You need at least BLOCKING diodes to keep
            power from going the wrong way to the wrong place. Bruce Roe

            Comment


            • #8
              I thank you very much for your help. I am now ok. Without which I would have remained confused. This although is an old thread

              Comment


              • #9
                Better late than never
                2.2kw Suntech mono, Classic 200, NEW Trace SW4024

                Comment


                • #10
                  If they have bypass diode then it will be more complex to get the things done easily.

                  Comment


                  • #11
                    Bypass Diodes in the Panels, do not perform the same function as a Blocking Diode (usually a special FET) in the controller.

                    Because of IR losses, you don't want to use a diode as a night time blocking diode. 1400 W @ 21V is 66A A 80A schottky diode with a .4V drop (on a big heatsink) will burn 26 watts in the daytime. A FET with even lower Vf can be wired for less than half that loss.
                    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                    solar: http://tinyurl.com/LMR-Solar
                    gen: http://tinyurl.com/LMR-Lister

                    Comment


                    • #12
                      MOSFETS look like a diode when turned off, a very low value resistor in either direction when
                      fully on. They may be paralleled to get an even lower resistance, positive resistance temp
                      coefficient means no problem with sharing. But you need the proper gate control circuit. Bruce Roe

                      Comment

                      Working...
                      X