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  • Originally posted by bistander View Post
    Hi Altrez and all,
    I've been working on a 4 cell LiFePO4 battery. Just got it to a point where I can start testing. I want to go through several cycles and purposely overvolt, overcurrent and unbalance cells to verify the BMS is working properly as well as check out my wiring.
    Cells are A123 brand LiFePO4, 26650 (26mm dia × 65mm long). Cells are a few years old but never used however appear to be disassembled from packs, probably DeWalt tool batteries. They are 3.3 volts nominal.

    Screenshot_20200808-220639.png
    [ATTACH]n499997[/ATTACH]

    And a couple photos:

    ​​ IMG_20200808_175554350.jpg

    IMG_20200808_175527203.jpg

    Just a short 'see if it works' test. Discharge at ~1A.

    IMG_20200808_175747093.jpg

    Next, a cell logger. It will keep track of the 4 individual cell voltages during the tests.

    IMG_20200808_175636586.jpg

    If tests go ok I'll heat shrink the 4 cells and BMS together in a nice little 2.3Ah 12V battery.

    Link to BMS if you're interested:
    https://www.electriccarpartscompany....agement-System

    Regards,
    bi
    Looks cool bi. I look forward to your testing! Do you know of a battery analyzer for the cells? It would be interesting to see that as well.

    -Altrez

    Comment


    • Hi Altrez,

      fourcellMod.png
      This is a download graph from the cellLogger. Blue trace is battery V and 4 other traces are individual cells. Cell #3 was under charged to start with. BMS did open circuit (turn off the battery output) when lowest cell (#3) hit 2.5V just like it supposed to. And as I monkeyed around with charge current from a power supply, it indeed did open circuit (prevents overcharge of any cell) on cue. However when left disconnected overnight, the BMS did little if anything to balance the 4 cells. So I've been manually equalizing cells today. Unless cells are equal in voltage and state of charge I won't get full capacity from battery.

      I have a few different cell/battery analyzers from the hobby industry for smaller capacities. I'll list or take photo of those once I get this thing balanced and on test. A lot of past experience was with medium capacity stuff like 10 to 100 Ah. Occasionally barrowed big high voltage/high ampere rig from nearby university, but most was done on homebuilt analyzers, meaning discharge and charge apparatus and data collection instruments.
      bi

      Comment


      • Altrez,
        Here's my collection of cell/battery analyzers.

        IMG_20200809_225543103_copy_1057x999.jpg It's been a while since I've used a couple of them. I think I'll need to try one of these on this new battery. Might just be that cell #3 is bad from the start. Ignored or forgot my own rule.... Test components prior to assembly.
        bi

        Comment


        • Originally posted by bistander View Post
          Hi Altrez,

          fourcellMod.png
          This is a download graph from the cellLogger. Blue trace is battery V and 4 other traces are individual cells. Cell #3 was under charged to start with. BMS did open circuit (turn off the battery output) when lowest cell (#3) hit 2.5V just like it supposed to. And as I monkeyed around with charge current from a power supply, it indeed did open circuit (prevents overcharge of any cell) on cue. However when left disconnected overnight, the BMS did little if anything to balance the 4 cells. So I've been manually equalizing cells today. Unless cells are equal in voltage and state of charge I won't get full capacity from battery.

          I have a few different cell/battery analyzers from the hobby industry for smaller capacities. I'll list or take photo of those once I get this thing balanced and on test. A lot of past experience was with medium capacity stuff like 10 to 100 Ah. Occasionally barrowed big high voltage/high ampere rig from nearby university, but most was done on homebuilt analyzers, meaning discharge and charge apparatus and data collection instruments.
          bi
          What product did you use to get that graph? I have been looking for something to do exactly that in the sub 1k range. I need standalone 8 channel 0-50 volts DC.

          Thanks!

          -Altrez

          Comment


          • Getting ready for my next round of tests!




            Any input on what tests I should be doing? I was just going to redo the Tests recommended by Turion but this time I am going to track watts on both the output of the battery and the charge to the battery.

            -Altrez

            Comment


            • Originally posted by altrez View Post

              What product did you use to get that graph? I have been looking for something to do exactly that in the sub 1k range. I need standalone 8 channel 0-50 volts DC.

              Thanks!

              -Altrez
              https://www.progressiverc.com/celllog-8s.html

              Discontinued. Too bad. Same thing, same functionality is unavailable. Per channel volt limit is too low for you. If I see something to fit your bill, I'll let you know.
              bi

              Comment


              • close
                https://www.icharger.co.nz/celllog-8s
                “Advances are made by answering questions. Discoveries are made by questioning answers.”
                —Bernhard Haisch, Astrophysicist

                Comment


                • Hey Altrez,
                  Turion found a possible source. The place is out of stock for the CellLog-8S and 8M (same as the 8S except w/o logging feature. They also list PowerLog-6S. 'out of stock' is not indicated. I used the PowerLog-6S years ago. Only 6 cells but also current and temp with logging. Might be worth a shot. Price is higher than it used to be and you're dealing with NZ. Check out the specs. All other sources I saw indicated out of stock. I believe it is also discontinued.
                  I've also used this:
                  https://www.dataq.com/
                  ​​​​You'd need to condition inputs over 10V. Simple voltage divider works. I'm sure I still have mine. Just misplaced it. It'll show up.
                  bi

                  {edit} If you're really serious, check this out:
                  https://www.dataq.com/products/graphtec/gl240/
                  I used it on a project. My colleague (computer science grad) set it up and I ran the tests with it and created the charts with Excel. A lot nicer and more capable than the little devices, but more $.

                  Originally posted by Turion View Post
                  Last edited by bistander; 08-11-2020, 04:11 AM. Reason: Added note

                  Comment


                  • Originally posted by bistander View Post
                    Hey Altrez,
                    Turion found a possible source. The place is out of stock for the CellLog-8S and 8M (same as the 8S except w/o logging feature. They also list PowerLog-6S. 'out of stock' is not indicated. I used the PowerLog-6S years ago. Only 6 cells but also current and temp with logging. Might be worth a shot. Price is higher than it used to be and you're dealing with NZ. Check out the specs. All other sources I saw indicated out of stock. I believe it is also discontinued.
                    I've also used this:
                    https://www.dataq.com/
                    ​​​​You'd need to condition inputs over 10V. Simple voltage divider works. I'm sure I still have mine. Just misplaced it. It'll show up.
                    bi

                    {edit} If you're really serious, check this out:
                    https://www.dataq.com/products/graphtec/gl240/
                    I used it on a project. My colleague (computer science grad) set it up and I ran the tests with it and created the charts with Excel. A lot nicer and more capable than the little devices, but more $.

                    I have the Dataq 10volt already. It's hiding somewhere in the house. it is a good logger I used it for my super cap tests in the old thread. The next one you posted is what I am looking for and only $995! I did say sub 1k lol thanks!

                    -Altrez
                    Last edited by altrez; 08-11-2020, 08:48 AM.

                    Comment

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