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some questions for SunKing, and anyone else on lithium battery technology

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  • #16
    Originally posted by gbynum View Post
    Thanks Sunking. So my original question; existing charger cuts off at 4.15 or so ... given that I don't need full energy stored, would I be better off to stop charging at 3.9 or 4.0 ... assuming I can determine how to do so?
    You are on the right track. LFP is the hardest to find because the charge discharge curve is so flat. Not so with any of the othersexcept LTO.

    Do you have the means to measure AH Discharge Capacity? Example many of the RC Hobby Chargers can charge or discharge any battery type. You can see what goes in, and what goes out. You would start by fully charging and then discharge and measure maximum capacity at 4.2 volts. Then Recharge to 4.1 volts and discharge, and so on until you get to where you want.

    Another way is you charge at 4.2 volts but terminate at a higher current than C/33. Example say it is a 10 AH cell instead of terminating at .3 amps, terminate at say 1 amp. Then do a discharge test to see where that lands.

    Assuming you cannot do a discharge test, you can use your flashlight and a timer. Fully charge it. then discharge in the flashlight until it goes dim and clock it. Lower the charge voltage a bit, repeat. If it goes 120 minutes on a full charge, you are looking for something like 100 to 110 minutes. If the flashlight is a single cell model, you do not have to worry about over discharge especially on LEd models. The driver will shut off before any thing can happen, You only worry when you have more than 1 in series. It takes another stronger battery to drive the weaker one into reverse polarity.

    So you are on the right track and just have to experiment a bit.

    If you really want to dive into it, here is a good [U][I][B]White Paper[/B][/I][/U] on the subject. You can cut to the meat on pages 9 and 10 graphs. But I can tell you from experience on a 3.6 vpc cell you charge until saturated @ 4.1 to 4.15 volts. That will get you 85 to 95% range. Another clue is Nissan Leaf battery max charge voltage is 4.1 on NMC batteries. No commercial EV manufacture allows the customer to fully charge a battery. They would go bankrupt if they did. They only time they allow it is at the end of life to get at that last bit of capacity they have been banking and saving for the end of life. Tesla did it already on older Roadsters and released the last top 20%. EV's operate 20/80 to 10/90 range. The golden rule is to stay away from the knees of the charge discharge curves.
    Last edited by Sunking; 06-02-2017, 05:04 PM.
    MSEE, PE

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    • #17
      Originally posted by karrak View Post
      ... sorry about not posting a clickable link, for reasons that are beyond me I am not allowed to post links.....
      Hogwash. You were banned from posting links because they were nearly all greenwash rubbish and were lowering this site's trust rating. You were warned for weeks/months about it.

      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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      • #18
        Originally posted by Sunking View Post
        If you really want to dive into it, here is a good white paper on the subject.
        Sunking, that link is to your system's filesystem ... C:/Users/Dereck/Downloads/energies-09-00900.pdf ... can you give me one that's accessible from outside? TIA, George

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        • #19
          Originally posted by Mike90250 View Post
          Hogwash. You were banned from posting links because they were nearly all greenwash rubbish and were lowering this site's trust rating. You were warned for weeks/months about it.
          Karrak cannot take a hint he is not welcome here. Just ban the SOB and be done with it.

          MSEE, PE

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          • #20
            Originally posted by gbynum View Post
            Sunking, that link is to your system's filesystem ... C:/Users/Dereck/Downloads/energies-09-00900.pdf ... can you give me one that's accessible from outside? TIA, George
            My bad, try again. I fixed the link.

            Here is a bonus from a very good friend of mine David Andrea. Another [B][I][U]White Paper[/U][/I][/B] on SOC. The bonus is once you get to that site is a wealth of information on Lithium batteries. Surf around, take your shoes off and stay awhile. He list every Lithium battery and every BMS there is with a ton of white papers and tutorial videos . You can spend a couple of days. David is an avid custom EV builder and BMS designer. If you can soak everything in David provides, you are well on your way.

            Just remeber SOC is basically an estimation or WAG. David makes it at least a education and gets you in the ball park WAG
            Last edited by Sunking; 06-02-2017, 05:14 PM.
            MSEE, PE

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            • #21
              Originally posted by sunking View Post
              my bad, try again.
              thanks!

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              • #22
                Originally posted by gbynum View Post
                thanks!
                You are welcome. Check the other link I gave you. I added more content for you in my last reply. Read David's site and I am sure you will have some excellent questions.
                MSEE, PE

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                • #23
                  One more huge treat for you. Everything there is to know about all batteries. This is the 3rd edition so it is free. Lithium is in there and the info still applies. It is the Mother Load of a book. I call it [B][I][U]THE BATTERY BIBLE.[/U][/I][/B] It will take you a week to read all 1500 pages. Months to get it to sink in.

                  [B][I][U]Forth Edition[/U][/I][/B] will cost you $150, so enjoy the free 3rd edition.

                  SK
                  Last edited by Sunking; 06-02-2017, 05:27 PM.
                  MSEE, PE

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                  • #24
                    Originally posted by Sunking View Post
                    Forth Edition will ...
                    Hmm, Forth edition ... I never got into Forth, my programming ceased after BASIC, Fortran, PL/1, and C. <big grin>

                    A HUGE THANKS! I'll enjoy skimming the book, but it may take more than a month.

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                    • #25
                      Originally posted by gbynum View Post
                      Hmm, Forth edition ... I never got into Forth, my programming ceased after BASIC, Fortran, PL/1, and C. <big grin>.
                      You are welcome. If al you are interest in is Lithium batteries, only two chapters to cover. Enjoy.

                      MSEE, PE

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