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LiFePO4 Batteries - Lithium Iron Phosphate

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  • #16
    Hello everyone,

    So I have received my LifePO4 batteries and I can now make some observations rather then speculation. I do intent to make my own post and shw some charge curves but I wanted to follow up once on this thread in case people don't follow to the other one.

    I want to speak to the balancing circuits again. I have tried charging up below the ceiling as I described and that method will work BUT you will not get the capacity out. When I did some charges to 14v I was only getting about 10AH out of a 20AH pack at a 5A rate down to 10.5v. That is done with a CBA. When I push all the way up I have pulled 19AH,, and 21AH a few times so it is important to push all the way up IF you need the full capacity. What I mean is you could under run them if you had enough cells to ensure you could meet your requirements but given the price of these cells it doesn't make sense to do that in my opinion. The thing that makes these cells special is that you can get more energy usage out of them safely, you can run them 80 percent or even more Dod making them stronger than their LA counterparts which really should only be brought down 50 percent or so. To put it another way you would need many more LA AH in your bank to get the same usage as with these.

    Another observation is that the cells I am testing do not rise and fall so equally as I thought. One of them was reaching 3.8v well before the rest although standing they were all within a few hundredths of a volt. This presents another problem. once these cells reach saturation they do not pass current so imagine a middle cell reaching capacity before the rest, it will sit there and damage itself while simultaneously starving it's partner cell down the string because it passes little to no current. LA will just gas off but these shut off basically.

    I am going to order some of the balance boards and see how that effects the charging, not sure if bedini tech will play nicely with them since these things are really meant to regulate high current and I am hitting them with spikes. If they are compatible I would say it is probably best to use them. As I have said you can run without them if your careful not to go to close to the top of the charge but personally I want the most capacity I can get out of these expensive cells and with the balancing circuits you probably don't have to babysit. For me it now hinges on whether or not feeding spikes through them is compatible.

    Of course this is all experimental stuff, I'm sure it all works wonderfully with the new trackers. I am just experimenting with spike charging as a curiosity.

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    • #17
      Hello to all, I bought some lifepo4 small AA cells, 3,6 volts each rated at 700 mAh.

      I have them in series, 4 AA, to make 12 volts batteries.

      I am charging them with a comparator cap dump but I have a doubt.

      In all places they say charge until 14,4 volts, but the cap dump don't raise the voltage that much as spikes or direct current. So for cap dump is a lower voltage?

      I charge 1 pack with cap dump until 13,34 volts, and then it rested at 13,2 volts.

      Should I try to push them higher even with cap dump?

      best,

      Alvaro

      Comment


      • #18
        Originally posted by BobZilla View Post
        Hello everyone,

        So I have received my LifePO4 batteries and I can now make some observations rather then speculation. I do intent to make my own post and shw some charge curves but I wanted to follow up once on this thread in case people don't follow to the other one.

        I want to speak to the balancing circuits again. I have tried charging up below the ceiling as I described and that method will work BUT you will not get the capacity out. When I did some charges to 14v I was only getting about 10AH out of a 20AH pack at a 5A rate down to 10.5v. That is done with a CBA. When I push all the way up I have pulled 19AH,, and 21AH a few times so it is important to push all the way up IF you need the full capacity. What I mean is you could under run them if you had enough cells to ensure you could meet your requirements but given the price of these cells it doesn't make sense to do that in my opinion. The thing that makes these cells special is that you can get more energy usage out of them safely, you can run them 80 percent or even more Dod making them stronger than their LA counterparts which really should only be brought down 50 percent or so. To put it another way you would need many more LA AH in your bank to get the same usage as with these.

        Another observation is that the cells I am testing do not rise and fall so equally as I thought. One of them was reaching 3.8v well before the rest although standing they were all within a few hundredths of a volt. This presents another problem. once these cells reach saturation they do not pass current so imagine a middle cell reaching capacity before the rest, it will sit there and damage itself while simultaneously starving it's partner cell down the string because it passes little to no current. LA will just gas off but these shut off basically.

        I am going to order some of the balance boards and see how that effects the charging, not sure if bedini tech will play nicely with them since these things are really meant to regulate high current and I am hitting them with spikes. If they are compatible I would say it is probably best to use them. As I have said you can run without them if your careful not to go to close to the top of the charge but personally I want the most capacity I can get out of these expensive cells and with the balancing circuits you probably don't have to babysit. For me it now hinges on whether or not feeding spikes through them is compatible.

        Of course this is all experimental stuff, I'm sure it all works wonderfully with the new trackers. I am just experimenting with spike charging as a curiosity.
        Bob,

        lifepo4 batts like current, its the nature of the battery. they like to be equalized thru discharge not charge. 14.8 is the finish voltage the trackers are set for with lifepo4. in the long term I am not sure they will play nice with the spike. they do like the linear regulator though....

        Tom C


        experimental Kits, chargers and solar trackers

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        • #19
          Bob,

          lifepo4 batts like current, its the nature of the battery. they like to be equalized thru discharge not charge. 14.8 is the finish voltage the trackers are set for with lifepo4. in the long term I am not sure they will play nice with the spike. they do like the linear regulator though....

          Tom C
          Thanks for the advice Tom. Now that I have had some time to play with these I agree that current seems to work the best. Second I would say a cap dump which is also current but not the same. I also tried just straight generator mode and mode one. All will charge them but i'm with you that over the long haul the spikes might cause issues or even the beating they take on a dumper. As far as just charging them the quickest with the least waste on an SG circuit i would say dumper, gen, and mode 1 in that order. Without question the most preferable way I have found is with my little tracker 3A, I have the regular LA model and it works great but I also have the boards Aaron recommends installed on each cell. In that setup you still don't want to let it keep going once they go red so it is not as noce as having the tracker with the correct calibration but as long as I keep an eye out it works very well.


          Hello to all, I bought some lifepo4 small AA cells, 3,6 volts each rated at 700 mAh.

          I have them in series, 4 AA, to make 12 volts batteries.

          I am charging them with a comparator cap dump but I have a doubt.

          In all places they say charge until 14,4 volts, but the cap dump don't raise the voltage that much as spikes or direct current. So for cap dump is a lower voltage?

          I charge 1 pack with cap dump until 13,34 volts, and then it rested at 13,2 volts.

          Should I try to push them higher even with cap dump?

          best,

          Alvaro
          Alvaro I cannot say much about the small AA's your working with but I have the 20AH packs and I can cap dump them to full charge so perhaps you just need to let them go a bit longer. Just as they discharge in more of a flat line pattern, they also flat line a bit on a charge so even if your not gaining voltage you may still be building capacity but I am only guessing since I do not have the AA's. Good luck ----Bob
          Last edited by BobZilla; 01-06-2015, 02:31 AM.

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          • #20
            Originally posted by BobZilla View Post
            Alvaro I cannot say much about the small AA's your working with but I have the 20AH packs and I can cap dump them to full charge so perhaps you just need to let them go a bit longer. Just as they discharge in more of a flat line pattern, they also flat line a bit on a charge so even if your not gaining voltage you may still be building capacity but I am only guessing since I do not have the AA's. Good luck ----Bob
            Tnx Bob, I will try to push them higher.

            best

            Alvaro

            Comment


            • #21
              You were right Bob, I was been impatient... they were stuck at 13.34 v but they keep charging and then reach 13.6 and from there to 15 they go very fast. tnx

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