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Solar water pump - Battery charging issues

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  • Solar water pump - Battery charging issues

    Hello everyone,

    I've have a little solar setup to pump water from creek up the hill to water tank:

    1) 12DC/10A diaphragm pump rated 160PSI
    2) etracer 20A MPPT controller
    3) 24V 120W solar panel
    4) 20A 12V AGM battery

    I've set the controller to switch off at 60% soc and switch on 80% SOC. When the SOC is around 60% and pump is not going I've noticed the controller doesn't send full 120W to battery but just around 50W. So it takes more time to get over 70% but when pump switches on and controller register load, it starts to push full 120W from the panel. As the pump consumes little bit more than the panel produces (this is intentional as I don't want to keep pump running long time) it goes down to 60% in ~2 minutes and switches off again. And the controller again sends only ~50W to battery.

    Does anyone have some idea what's going on? Is it because the controller "thinks" the battery is still charged so uses equal/float charge instead of boost or something like that?

    I designed the system so it would pump for 2 minutes and then stop for ~1 minute so I don't burn the pump.

    BTW the pump should push 5 litres per minute but since I pump around ~80m up hill it delivers only 1.5l/m (which is still fine for me)...

    Any advice would be really appreciated!

  • #2
    It looks like perhaps the CC does not switch back into Bulk mode after reaching Absorb or Float unless the voltage drops farther than you want it to.
    When you say "the controller" are you referring to the pump controller? Or to the LOAD output of the CC?
    What sort of user setting are available on the etracer CC?
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    • #3
      Originally posted by nztomas View Post
      1) 12DC/10A diaphragm pump rated 160PSI
      2) etracer 20A MPPT controller
      3) 24V 120W solar panel
      4) 20A 12V AGM battery

      I've set the controller to switch off at 60% soc and switch on 80% SOC. When the SOC is around 60% and pump is not going I've noticed the controller doesn't send full 120W to battery but just around 50W.
      Lucky you get that much.

      The problem is you have a tiny watch battery on a monster sized solar panel. Your tiny little battery, 12 volt @ 20 AH cannot take a lot of current, 4 or 5 amps at most. Small tiny batteries have high resistance. So even if the battery is discharged, when you try to hit it with 10 amps from the panel causes the voltage to shoot up and fool the controller into thinking the battery is charged and it shuts off or folds back. Otherwise it would just cook your tiny little battery.

      Two ways to fix this take your pick.

      1. Get rid of the solar panel and get you a 20 watt panel to replace it. Really bad idea though.
      2. Get rid of your tiny little battery and get a minimum 12 volt 100 AH battery or up to 130 AH

      Panels, charge controller, battery, and load all have to be matched up to work together. You have nothing matched up to work with each other or to do what you want. You just threw something together and hoped it would work. It failed.

      A load that demands 10 amps needs a minimum 100 AH or larger battery. You only have 20.
      MSEE, PE

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