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Panel not charging my SLA 12V battery

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  • #16
    Originally posted by agdodge4x4 View Post
    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.
    Laugh - like so many solar projects, where is he NOW? That project was built and documented over 1.5 years ago. Many online projects are like this - cobbled together enough to work to make the initial documentation / video. Then nothing about all of it thrown into the corner of the garage.

    First, he killed his first battery with no controller for an undersized panel - which WILL kill a battery eventually. And no blocking diode it seems. No mention of solar insolation hours. I do note that this project was documented in the SUMMER as well. Not a solar engineer, even amateur. Just throwing stuff against the wall.

    The point is, you are grossly underpowered for your load for *real world* conditions. Also consider that the battery you are using is a small agm, and at 7.5ah is usually one designed for a ups, not repetitive cycling. Add to that retail storage factors without charge and a whole host of other factors to make that battery pretty sad once it reaches your doorstep.

    Try again - get a common 18ah agm, (which will help limit your DOD, and 40 - 60 watts of panel. You'll be much happier. Put a battery charger on it before starting out. Don't use a crappy ping-pong type of controller. Go with a simple Morningstar, Steca, Xantrex, or the like.


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    • #17
      Thats too expensive. I have a 15W panel, and I can get a deep cycle battery or 18AH battery, but the panel is not getting any bigger. I have space and budget requirements.

      So I need to figure out the max number of Amps a light can draw for 6 hours a day (or 3 as a minimum) within the confines of the parameters listed above to make the system work every day. I will have to change the light output instead.

      FYI: Using the link quoted earlier by SunKing I need a 15W panel and 6 AH of battery for running this 2.4W light for 6 hours. That includes dumbing down the solar insolation to 2 hours, though its actually more like 3.5. That also is in line with about 3 online calculators give or take.

      Is there a fudge factor I missed?

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      • #18
        Originally posted by agdodge4x4 View Post
        Thats too expensive. I have a 15W panel, and I can get a deep cycle battery or 18AH battery, but the panel is not getting any bigger. I have space and budget requirements.

        So I need to figure out the max number of Amps a light can draw for 6 hours a day (or 3 as a minimum) within the confines of the parameters listed above to make the system work every day. I will have to change the light output instead.

        FYI: Using the link quoted earlier by SunKing I need a 15W panel and 6 AH of battery for running this 2.4W light for 6 hours. That includes dumbing down the solar insolation to 2 hours, though its actually more like 3.5. That also is in line with about 3 online calculators give or take.

        Is there a fudge factor I missed?
        You are only looking at one side of the equations. You can size your battery to run your load but you also have to size the charging system (pv panel/cc) to put back 120% what you took out of that battery. That will take much longer than 2 hours. If you do not perform a good charge that battery will continue to reduce it's 6Ah rating and last a day or so and then die. Which is where you came in with your first question.

        "Panel not charging my SLA 12V battery". And unless you get a bigger panel or more sunlight, your new battery will not last very long.

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        • #19
          Originally posted by agdodge4x4 View Post
          FYI: Using the link quoted earlier by SunKing I need a 15W panel and 6 AH of battery for running this 2.4W light for 6 hours. That includes dumbing down the solar insolation to 2 hours, though its actually more like 3.5. That also is in line with about 3 online calculators give or take.

          Is there a fudge factor I missed?
          Yeah you are assuming the light Fixture only pulls 2.4 watts which is most likely a big lie. Most likely they mean the LED consumes 2.4 watts, but the fixture with the Driver burns 5 watts. They do not count the Driver power and the losses.

          Lastly you are not going to find a True Deep Cycle 6 AH battery. All you will find is UPS batteries and they are not deep cycle. 12 volt Deep Cycles start at around 40 to 50 AH and that takes a minimum 40 to 60 watt panel.

          You are learning a very good lesson. Solar is very expensive. Too bad you have to learn that the hard way with your money. If you had researched and listened, you could have figured that out for FREE.

          Good Luck.
          MSEE, PE

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          • #20
            Originally posted by Sunking View Post
            Yeah you are assuming the light Fixture only pulls 2.4 watts which is most likely a big lie. Most likely they mean the LED consumes 2.4 watts, but the fixture with the Driver burns 5 watts. They do not count the Driver power and the losses.
            Thats a piece I was missing. Im going to redo my calcs with 5W. I KNOW what I need because you all told me, but I want to arrive at that on my own.

            *One thing I still do not understand is that I plugged this light in and ran it, and I measured the Amperage with my multimeter. It measured out at .24 AMPS.....would that not include the drivers and LED as a unit?

            *What if I utilized a 15W panel, deep cycle marine battery, and only turned the light on once a week manually when it was needed for a few hours? Would that be safe for the battery?

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            • #21
              Originally posted by agdodge4x4 View Post
              *One thing I still do not understand is that I plugged this light in and ran it, and I measured the Amperage with my multimeter. It measured out at .24 AMPS.....would that not include the drivers and LED as a unit?
              Absolutely, it gives you the real wattage. Assuming 12 volt x .24 amps = 3 watts

              Forget about amp hours as it is just the end result. If I were to ask you how much energy is in 15 AH battery , you could not possible answer the question. No matter how you answer, I can prove you are wrong. Example if you said 180 watt hours you would be dead wrong. Know why?

              Because I am playing games with numbers. You are most likely trapped inside a 12 volt box. I am not. I would say you are wrong. My electric motorcycle uses a 300 volt battery 15 AH battery and it has 4500 watt hours. My point here is Amp Hours is meaningless, just the end result. Work with WATT HOURS.

              Example lets say you want to burn that 3 watt LED 10 hours per day. You are using 30 watt hours right? Right. You are going to use a PWM charger, so double that to 60 watt hours. You check Solar Insolation and in December you may have 2 Sun Hours. What panel wattage is needed? Panel Wattage = Watt Hours / Sun Hours. 60 wh / 2 sh = 30 watts.

              OK what size battery? First thing you have to decide is what voltage and that depends a lot on panel wattage. 500 watts and lower you can use 12 volts. So now we know the voltage is 12 volts. What AH? Here is your second mistake. Minimum must be 5 days capacity. I will explain why in a moment, there are several reasons. So AH = [Daily Watt Hours x 5] / Battery Voltage. So [30 wh x 5] 12 volts = 14.5 AH. As you can see AH was just the final result.

              There are several reasons to use a 5 day reserve capacity:

              1. Most Important is it is the best economic solution. The deeper you discharge a battery, the fewer cycles it will have. If you discharge only 20% each day you can get up to 1000 cycles or 3 years. Discharge it 50% per day, and you are lucky to get 250 cycles of less than a year. You would go through 3 batteries vs 1.

              2. CYA for cloudy days. You never want a lead acid battery to go below 50% or you really accelerate aging. So wiht 5 days reserve gives you about 3 days of no sun.

              3. Now here is where you really get screwed. Mr Peukert will rob you blind if you discharge the battery at more than the 20 hours discharge rate. What that means is let's say you have a 100 AH battery. It is rated at 100 AH at the 20 hour discharge rate. Amps = Amp Hours / Hours. So the 20 hours discharge rate on a 100 AH battery is 100 AH / 20 Hours = 5 amps.This is where Peukert Law comes into play which simply states; As the rate increases, the battery's available capacity decreases. So what happens if we say discharge that 100 AH battery at:

              10 hours the battery capacity becomes 85 AH
              5 hours...... 65 AH
              2 hours...... 50 AH
              1 hour........ 35 AH
              100 hours ......135 AH

              Last note here when you look up Sun Hours, that spec means you must have clear view of the horizon to the East, South, and West with absolutely no SHADE. Just the shadow of a single leaf will shut your panel down. It must also face directly Solar South with the correct Tilt Angle. Any deviations and throw all the numbers away.
              MSEE, PE

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              • #22
                OOOOOHHHHHhhhhhhhhhhhhhhhhhhhhhhhh. I see. Im going to soak this up for a while and put this on paper to digest.

                For what I am seeing, if I understand this post on the surface, this light, burning 3 watts, even only 3 hours a day would have 5 days of capacity on this chinzy 7.5AH batter IF the battery was brand new, and IF all other conditions were pretty much absolutely 100% perfect. With an old battery, a panel that is not receiving clear site horizon to horizon....it hasnt a prayer in the world of accomplishing what I wish to accomplish.....unless I used it occasionally and it sat on trickle charge most of its life.

                (Which is exactly what you all told me, but this way I understand a bit better why this is the case)

                Thank you for all of this information. I can still make this work within my setup, but its usage would have to be pretty limited....NOT every night for hours on end. It won't work like that.

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                • #23
                  Originally posted by agdodge4x4 View Post
                  For what I am seeing, if I understand this post on the surface, this light, burning 3 watts, even only 3 hours a day would have 5 days of capacity on this chinzy 7.5AH batter IF the battery was brand new, and IF all other conditions were pretty much absolutely 100% perfect. With an old battery, a panel that is not receiving clear site horizon to horizon....it hasnt a prayer in the world of accomplishing what I wish to accomplish.....unless I used it occasionally and it sat on trickle charge most of its life..
                  Sounds like you are starting to get it. Keep in mind the Insolation Tables are based on ideal conditions.
                  MSEE, PE

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                  • #24
                    Man..someone spammed my post! Well, since IM here, figured I would update everyone. My single light has been running off of my 15W panel and garden tractor battery for about 3 hours every night. Thanks to all, again, for pointing me in the right direction!

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                    • #25
                      Howdy agdodge4x4, thanks for popping in, I think I will delete that nasty self promotional spam from some crappy chinese inverter company, we cant have that tripe clogging up a good thread now

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                      • #26
                        Any one wants to know what exactly is going on with their system large or small should have a couple of these meters on hand... Works great for me....
                        You could had used two 10 watt panels but faced one eastward and one westward...
                        Last edited by MetricAmerica; 05-29-2016, 07:13 PM.

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