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  • Adding additional bank

    So I know that manufacturers do not recommend mixing older with new batteries. However, the batteries I have (x 8 us battery 2200xc) after 15 months of service are still 100% spec for a new battery per the manufacturer and I.e are still showing strong SG levels in all cells between 1,275 -1,280 @ 25deg after full charge.

    I want to add a second bank of 8 to make 16 batt in total (48volt sys). Seems like it would be ok, but am I missing something.

  • #2
    I think you answered your own question. Based on what you said about you older batteries, you'll be fine. Worse case you'll see a little drag on the new ones and they will level out with the older ones. I'd commission them and get as close in SG level as you can and enjoy the new capacity. Maybe do a short EQ on the older , then do the same on the new ones and then combine them.

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    • #3
      Originally posted by Willy T View Post
      I think you answered your own question. Based on what you said about you older batteries, you'll be fine. Worse case you'll see a little drag on the new ones and they will level out with the older ones. I'd commission them and get as close in SG level as you can and enjoy the new capacity. Maybe do a short EQ on the older , then do the same on the new ones and then combine them.
      Yes, to an extent I am asking a question I think I know the answer too. Th idea is to get opinions from others just to make certain I am not missing something.

      The fact that SG levels are per spec means the battery has not lost capacity form new, this is how I understand this. Therefore, if the batteries are at spec, the new batteries will not be "pulled down" to their capacity as existing batteries are still as like "new" from a capacity point of view.

      The question is do batteries go along at full spec for some time and then quite rapidly start losing capacity? Also, the additional bank will reduce the DOD significantly, so that should also help to slow down capacity loss. I assume?!

      As US battery told me that they even consider 1,265 at spec and let batteries out of their warehouse with those SG's.

      But, still perhaps there is another factor one of the very techie guys can raise that I am not considering.

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      • #4
        Originally posted by Jemplayer View Post

        The question is do batteries go along at full spec for some time and then quite rapidly start losing capacity? Also, the additional bank will reduce the DOD significantly, so that should also help to slow down capacity loss. I assume?!
        The first 20-100 cycles when deep cycle batteries are put into service the batteries go from 75% to 100% capacity as the plates form and become active. Then as long as you keep the SG"s up they go through a period of several years where the capacity remains fairly flat. As all batteries have a expected life based on the plates of 4-10 years they will begin to lose capacity as they age. The curve on the out years is gradual, but noticeable. While the Industry standard says when a battery reaches 77-80% of rated capacity it's service life is over. Now in RE most will try to use them to 50% if the can still get you through the night with your loads.

        This chart really about how a slight undercharge would extend the life of a battery, but it works for your question.

        ScreenHunter_862.jpg

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        • #5
          Originally posted by Jemplayer View Post

          The fact that SG levels are per spec means the battery has not lost capacity form new, this is how I understand this. Therefore, if the batteries are at spec, the new batteries will not be "pulled down" to their capacity as existing batteries are still as like "new" from a capacity point of view.
          Take two batteries paralleled , one new and one 15 months old. When you apply a load they will both drop to a voltage level to sustain the load. The newer one will drop less in voltage to sustain the load. After the load is removed the batteries will recover to a voltage level. The level will not be the same because the older battery will have lower capacity. It's at this point that the older battery will begin to " Pull Down" the new battery to it's voltage level as they even out. It happens other times, like removing them from a float charge, but you should get the concept.

          Now, what issues do you think will arise when you combine the two strings, one set that have already reached 100% capacity and one new string without formed plates at 75% capacity ?? They will even out.

          Battery Manufacturers use all kind of terms that are meaningless except to them. At spec, who knows what it means. Both batteries could have 1.265 sg level and be very far apart in capacity. I could take a battery and pull it to 80% dod every day for 15 months and the SG could be the same and I'll guarantee you they would not even be close in capacity.

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          • #6
            Originally posted by Willy T View Post
            Battery Manufacturers use all kind of terms that are meaningless except to them. At spec, who knows what it means. Both batteries could have 1.265 sg level and be very far apart in capacity. I could take a battery and pull it to 80% dod every day for 15 months and the SG could be the same and I'll guarantee you they would not even be close in capacity.
            One thing that you can count on, though, is that if the SG of a battery at full charge (as determined by the SG no longer rising with additional charging current) and the SG is lower than it was when the battery was new then the battery has lost a noticeable amount of its sulfuric acid content to hard sulfation on the plates. And that does correspond to a loss in capacity.
            The inverse (that high SG means no loss of capacity) is unfortunately not true.
            SunnyBoy 3000 US, 18 BP Solar 175B panels.

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            • #7
              Originally posted by inetdog View Post
              One thing that you can count on, though, is that if the SG of a battery at full charge (as determined by the SG no longer rising with additional charging current) and the SG is lower than it was when the battery was new then the battery has lost a noticeable amount of its sulfuric acid content to hard sulfation on the plates. And that does correspond to a loss in capacity.
              The inverse (that high SG means no loss of capacity) is unfortunately not true.
              Sg's are the same as when batteries where 4 months old. What you say above is interesting. Per the manufactures tech, if the sg is at spec then capacity is 100%. They told me that as capacity decreases with age it will reflect in the sg level dropping over time.

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              • #8
                Specific Gravity isn't what would matter. Internal resistance is what matters in parralleling batteries. I seen no reference to checking the IR of the batteries.

                I'd guess you could expect the new batteries life expectancy to be reduced between 25% to 50% if you parrallel them with the old batteries.

                WWW

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                • #9
                  Originally posted by Wy_White_Wolf View Post
                  Specific Gravity isn't what would matter. Internal resistance is what matters in parralleling batteries. I seen no reference to checking the IR of the batteries.

                  I'd guess you could expect the new batteries life expectancy to be reduced between 25% to 50% if you parrallel them with the old batteries.

                  WWW
                  And how would one go abut texting IR?

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                  • #10
                    Originally posted by Jemplayer View Post
                    And how would one go abut texting IR?
                    Sunking has a thread on it somewhere. I think it might even be a sticky.

                    WWW

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                    • #11
                      http://www.solarpaneltalk.com/showth...nal+resistance

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