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  • Panel not charging my SLA 12V battery

    I have a strange setup, but I think it will apply here. I have a 10W solar panel hooked to a solar charge controller. Then I have a small LED flood light hooked up to the battery via a photo sensor. This is actually used to illuminate a wildlife feeder to watch bobcats and coyotes.

    Anyway, the solar controller has a shutoff and diagnostic LED and it indicates that my battery is 'low'. Its currently at 11.5V. It wont let the light come on at night. The light doesnt draw much. ITs a 12v SLA battery. The issue is that the panel is 10W and in DIRECT sunlight facing south for at least 6 hours. It should EASILY charge this battery, but for some reason, it is not doing it. I have another charge controller that is also not working for it, so I don't think its the controller. The battery is in good shape and will take and keep a charge if charged with a trickel charger.

    Is there something I can check? Its frustrating. I have a tiny 5W that has NO controller that charges the exact same battery for the camera, and its holding a solid 12.7V. So...something isnt right with my big panel.

    What can I do to troubleshoot this?

    Here is the controller:

    http://www.amazon.com/dp/B00NAR1NM4/...lar+controller

  • #2
    How many watts does the LED flood light pull? How long is it on each day? How many Ah is the battery?
    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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    • #3
      I can't remember the exact numbers for the light, but when I ran a test for a few nights, the voltage on the battery dropped less than 1V in a 12 hour period. That was from a FULL charge. The light is not currently on 6 hours. Battery is a 7.5AH. I didd run a test with the light to measure the amp draw, but I cannot remember. I THINK i remember it being somewhere in the ballpark of .2A. But I cannot be sure now and I dont have my notes. I tossed all of that once I decided that a single SLA battery was more than enough to handle the task. Not sure if that helps.

      The light is a 10W light, but even at 12V, it did not pull the 10W. I measured curent with my multimeter. Moreover, its a light that has multiple colors. The only way it pulled 8W was using the WHITE function. I use RED, and that was pulling .2A I THINK...that kind of makes sense considering 1/3 of the LED are on when using RED.

      Comment


      • #4
        This is super easy to figure out. Like 90% of the people who come here, your system is grossly undersized.
        • You have a 10 watt panel at best generates 20 watt hours a day on a really good day if you are lucky
        • You have a battery that can only supply 20 watt hours a day.
        • You have a light that takes 100 watt hours per day.
        You failed basic math. You are bankrupt.Only way to make this work is to only use the light 1 to 2 hours per day, after you let the battery recharge for a week. . Simple 5th grade math.
        MSEE, PE

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        • #5
          What? A 7.5AH/20Hr battery is 90 Watt hours. No?
          Light is .2A, 12V for 6 hours....thats 14.4 Watt hours ...but thats not what you came up with.


          Walk me through this. I need to know exactly how to make the calculation.

          I'm lost because I thought a 7.5AH battery can handle .2A light for 37 hours....and that seemed reasonable considering I used the light on this battery two nights in a row WITHOUT a recharge, and that left me at 11.5V (or something really not that much). But apparently, that is not all there is to the equation.

          Let's work with a .2 Amps for the light, running 6 hours per night max, 12v SLA 7.5AH/20Hrs battery and the 10W panel. Help me through it. I can't get my head around a fully charged battery dropping less than 1V after TWELVE hours of full light use and the 10W panel not being able to essentially top that off. That may be where my hangup is.

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          • #6
            Figure it out yourself. Read This Sticky
            MSEE, PE

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            • #7
              Sure enough, 7.5ah * 12v = 90 watthours. BUT only half of that is usable for a 50% DOD to get any cycle life out of it. So you really have 45 watthours to play with.

              This is winter. 6 hours of direct sunlight are not the real solar isolation hours that count . Depending on where you are, it is more like 2 - 4 hours. Solar isolation hours are different than sunrise to sunset.

              To make matters worse, to fully charge an agm battery, that means you need at least 6-8 hours of float!! Each cycle! If you dont, the capacity walks down progressively from sulfation of the little bit that never gets charged and hardens.

              What you are looking at is at least doubling your battery capacity, and quadrupling your panel power.

              And unfortunately your 7.5ah battery is toast now.

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              • #8
                I will revisit the sticky.

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                • #9
                  Originally posted by agdodge4x4 View Post
                  What? A 7.5AH/20Hr battery is 90 Watt hours. No?
                  Light is .2A, 12V for 6 hours....thats 14.4 Watt hours ...but thats not what you came up with.


                  Walk me through this. I need to know exactly how to make the calculation.

                  I'm lost because I thought a 7.5AH battery can handle .2A light for 37 hours....and that seemed reasonable considering I used the light on this battery two nights in a row WITHOUT a recharge, and that left me at 11.5V (or something really not that much). But apparently, that is not all there is to the equation.

                  Let's work with a .2 Amps for the light, running 6 hours per night max, 12v SLA 7.5AH/20Hrs battery and the 10W panel. Help me through it. I can't get my head around a fully charged battery dropping less than 1V after TWELVE hours of full light use and the 10W panel not being able to essentially top that off. That may be where my hangup is.
                  That tells me that your load is much larger than you're claiming or the battery was shot to begin with. A voltage of 11.5 would be less than 20% charged. So each night you used over 35WH. Your panel cannot supply that this time of year. Being December and living someplace that has bobcats leads me to believe you have less than 1 hour of solar insolation available.

                  WWW

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                  • #10
                    Am I understanding this:

                    Battery is 7.5AH 12V

                    Light uses .2 amps...so thats 2.4W. If I run for 6 hours, then that is 14.4 WH.

                    14.4WH is 1.2AH at 12V. And 1.2AH is .16 or 16% discharge?

                    If I assume a safety factor of 50% for the battery, then that leaves me with a 3.75AH battery, effectively which means I have discharged 32%.

                    Is that right?

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                    • #11
                      The battery is no longer 7.5 Ah. If you've routinely run it below 12 V, and have not been charging it as PN Junction described, the capacity has been degraded. As he pointed out, if running it just two nights without charging took it all the way down to 11.5 V (almost definitely damaging it in the process), either your load is much higher than the 0.2 A you are thinking, or the battery is in very bad condition.
                      CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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                      • #12
                        Let's try to focus on the calculation I just made and assume the battery is brand new with full capacity so I can understand the concepts with known values. The actual battery may be 6 months old or 4 years old and it could be one that is not on a panel, which means its been run down to 10.5V multiple times a year before its recharged and put back out in the field. I have a box of batteries So, let's just remove that part of the variable and pretend we are working with brand new batteries.

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                        • #13
                          Batteries need to be recharged with about 120% of what was withdrawn from them. As they age, that 120% changes to 125% to 130%.

                          The speed of the withdrawal also matters, batteries are rated at a 20 hour rate, (usually) So a 10ah battery can supply half Amp for 20 hours and then it is totally flat,
                          If you consume more than that half amp rate, even for 5 minutes, that drives the battery into an inefficient state, and you loose capacity. Same for recharging too fast, the battery cannot accept that power, and as soon as the charge stops, the voltage crashes. It's called Peukert's law https://en.wikipedia.org/wiki/Peukert's_law

                          Panels produce 80% of their rated power, for the number of hours they are properly aligned with the sun,
                          Alignment off = much less power harvest fixed panels are only aligned for 20 minutes of the day
                          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

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                          • #14
                            So you guys are pretty confident my .278A light won't run right unless I use a battery twice as big and a panel 4 times bigger? http://www.predatormastersforums.com...Number=2686264 This guy disagrees. And so does the calculator he used. Obviously his battery is much bigger, but the panel sure as hell is not 4 times larger.

                            3 OR 6 WATT LIGHTS?

                            Why does this setup work? This should run the light longer every day, but the panel shouldnt be able to bring it back to a fully charged state, so eventually its capacity should be no good.

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                            • #15
                              Originally posted by agdodge4x4 View Post
                              This guy disagrees. And so does the calculator he used.
                              Who do you want to believe?

                              I am a professional engineer that has been doing this for 35 years, and you have two more pros telling you are wet behind the ears. It took me less than 5 seconds to do the math in my head. Your own results tell you exactly who is right. So who you going to believe? The truth, or what you want to hear?

                              You 10 watt panel is not even enough to charge a cell phone in a day. A battery with 11.5 volts is a boat anchor.
                              MSEE, PE

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