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Why does it drop so fast?

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  • Why does it drop so fast?

    I have a small cabin w/ solar system that I recently bought and am new to the game. Its a 12v system w/ 2 panels and 2 batteries (agm sealed 200ah 12v). I can have a good charge like 12.6,12.7 and then I will use it for a bit (like a couple of leds lights and cell phone charger) and after a short period of time (2,3 hours sometimes), at night, the charge controller reads it is like 11 give or take a bit and then shuts down from low voltage. It will go off and then in a bit of time (couple of minutes or more), it will say 12.5ish and work again.
    I thought it might be a bad charge controller (it is a Morningstar Prostar PS-30M) and got another (cheap one this time) and it did exactly the same.

    It seems with any load, the voltage drops quickly and then comes back when load is off [when solar is not charging].
    Can someone explain whats going on?
    Thanks,
    JB

  • #2
    Batteries are shot.

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    • #3
      I was worried this is the case. They are not old and I brought them in to the place purchased and they said they were fine. How can I/they tell? They seem to hold a charge (when no load is on)? They were $350 each, so is a harsh expensive to replace.
      Thanks.

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      • #4
        Originally posted by theborland View Post
        I was worried this is the case. They are not old and I brought them in to the place purchased and they said they were fine. How can I/they tell? They seem to hold a charge (when no load is on)? They were $350 each, so is a harsh expensive to replace.
        Thanks.
        You may not have been charging them properly (wrong voltage setting on the charger?) or the batteries may have been sitting to long in the distributor's storage without being charged. If these are not sealed batteries you should start by measuring the Specific Gravity of the electrolyte with a temperature compensating hydrometer.
        Then try charging (at a higher voltage) until the SG stops rising.

        But the chances are good that the batteries cannot be recovered.

        What brand and model are they?
        What are the voltage settings on your CC?
        What ambient temperature are the batteries at?
        SunnyBoy 3000 US, 18 BP Solar 175B panels.

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        • #5
          Have you checked the torque on all connections?
          Battery to CC, battery to distribution fuse panel. connections at panels and CC. If they are loose or corroded you will have problems. futile to do a load test until all connections have been inspected. I suspect your array is too small for the batteries and PWM CC. Your batteries are likely shot either way. have you checked the water? when is the last time you started the generator and hit them with a good stiff charge?

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          • #6
            Did they run a load test on the batteries? If not, take them in again and have them load tested.

            If so, then double check all the connections.

            WWW

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            • #7
              Thanks all for the ideas. Im going to cabin this weekend; Ill check on questions I dont know.
              As to questions that I know answers of:
              I'll check connections.
              The shop said they tested and they were fine (dont know how serious a check [took like 2 minutes max]
              They are sealed, so I cant check levels.
              They are stored year round outside (under cabin), but with full charge.
              Its true panels are undersized, but useage is minimal (one night a week) and only for lights/cellphones.
              Ill get back after checkign things out a bit more,
              Thanks all,jb

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              • Logan5
                Logan5 commented
                Editing a comment
                When was the last time you hit them with a good stiff charge? Not solar. Like start and charge them from generator?

            • #8
              Did you initialize these batteries before you placed them in a solar charge situation?

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              • #9
                Originally posted by theborland View Post
                They are sealed, so I cant check levels.
                Are they truly sealed, as in AGM or GEL battery type?
                Or are they just "maintenance free" flooded lead acid batteries with very hard to open vent covers?
                There is a difference between the two types in performance and resistance to damage from undercharging.

                SunnyBoy 3000 US, 18 BP Solar 175B panels.

                Comment


                • #10
                  What wattage are the panels? Is total capacity of the batteries 200 AH

                  During the day you should see th evoltage go up to near 15 volts, then cut back to 13,6 volts after the batteries are charged up with solar on. After sunset the voltage will fall to 12.6 volts and is normal. Under load, the voltage will sag a bit and normal. However they should only sag no more than .2 to .3 volts under heavy load.

                  You need to bring the batteries home and give them a good charge and test them. You cannot use solar to do that. If I had to guess and the reason I ask what panel wattage and battery capacity you have is I strongly suspect is your batteries are grossly under charged from way to low panel wattage. 99% of the folks who come here are grossly mismatched. You are trying to pull a train with a bicycle.

                  Assuming you are using an PWM controller with battery panels (most common mistake along with using battery panels) a 12 volt 200 AH battery requires 360 to 400 watts of panels. Do you have that much power? With a MPPT controller requires 240 watts.
                  MSEE, PE

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