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    Trying to understand battery.

    I bought this battey
    http://www.ebikes.ca/shop/electric-b...16-lim-dt.html
    the spec say 52V Nominal and 16.5 Ah (but when I received it, it was written 17.52, good for me I guess)
    from the Battery Spec pic below, I see that the Cell are Panasonic NCR18650GA and with this I found those spec
    https://www.orbtronic.com/content/Da...GA-3500mah.pdf
    it say 3.6V nominal and 3.45 Ah

    now the question

    1-
    to calculated the energy in the battery I did
    52V * 17.52 = 911 Wh.
    it that ok ?


    2-
    to get 52V I guess there is 52V / 3.6 V/cell = 14.4 cell in series
    it that ok ?


    3-
    from the Spec Pic, I see
    14S
    and
    14S * 5P
    the 14 S , my guess was 14 cell but was about the 5P ?
    is that 5 lignes of 14S in parallel ?


    4-
    if #3 is correct
    I would calculated the energy for one ligne at
    3.6V/cell * 14 cell * 3.45 Ah = 173.88 Wh
    and 5 in parallel would give a 173.88 * 5 = 869.4 Wh

    but because I see a 17.52, instead of 16.5 , I guess my calculation are wrong


    5-
    from the 18650 spec, I am trying to found the discharge rate and Charge rate
    I know I am suppose to look a CC but I can't figure it out


    6-
    from the battery link, read
    "52V 16.5 Ah Downtube Battery with Panasonic GA Cells,"
    what is Downtube



    thank you, :-)



    #2
    The voltage will vary from start to finish considerably and differently depending on loads so there's no way to come up with precise numbers - having said that...

    1 - the math is right but is impacted by my preface - from the datasheet the battery is 16.5Ah and 16.5Ah · 52V = 858wh

    2 - 52V will be a 14s[eries] - 14 · 3.7V (nominal) = 51.8V = ~52V

    3 - 14 s[eries] x 5p[arallel] will generally be 14 groups of 5 parallel cells with the 14 groups in series

    4 - given 3300mAh (from the datasheet you linked to!) then the battery mAh is 5x - 5 · 3300mAh = 16.5Ah as the manufacturer specifies

    5 - I don't understand the question or comment here

    6 - downtube is the tube that runs from the steering head to the crank where the battery is intended to mount

    Comment


      #3
      Regarding Question 5, from another site/datasheet:

      Specifications:
      Nominal Capacity: 3500 mAh
      Nominal Voltage: 3.6V
      Discharge End Voltage: 2.5V
      Standard Charging Current: 1.475A
      Charging Voltage: 4.20+-0.05V
      Max. Continuous Discharging Current: 10A
      Dimensions:
      65.3mm (L) x 18.50 mm (D)
      Weight: 48.0g

      Since you 5 in parallel, for the pack:
      Standard Charging Current: 1.475A x 5 = 7.375A (but less is better for battery life)

      Max. Continuous Discharging Current: 10A x 5 = 50A

      Comment


        #4
        AZguy and Fred answered to the questions more than fully. I want to add a couple of words - at 10A discharge rate (the max allowed for a GA cell) the capacity of a single cell would be ≤3.25-3.30Ah. Taking into account the 3.6V nominal voltage we would have 14x5x3.6x3.30=831.6Wh max at full load.
        Also there are 2 versions of GA cells - Chinese made and Japanese made, which differ slightly. Japanese cells are better.

        Comment


          #5
          Wow !! Thank you all for those precise and fast answer.

          I am impress with the Discharge rate
          I was not sure about the way I understood battery, I feel more confident now.

          Oh, where should I setup the cut off tension. I currently set it a 41 Volts,

          1- Should I put it higher ?

          Comment


            #6
            I do have more question about battery but I do not know if it is better to post them here or to move to another thread.

            Just in case, Here they are.
            I have built a solar eBike
            https://www.flickr.com/photos/157268676@N03/albums

            everything are working well, but now I realize I Might have made some bad design choice :-)

            The output of the solar panel goes to 2 MPPT Converter/Charger and then to the Charging port of my battery.
            The output port of the battery goes to the motors
            the MPPT adjust the V to charge the battery.


            My panel produce around 340 Watts on a typical day.

            2- that mean I would have 340/53 = 6.4 Amp charging the battery ?


            I would be below the max of 7.375A that Fred found but still a little bit high.
            I understand that the faster I charge the battery, the shorter life it will have.
            if I have a 8 hours day at 340 watts, = 8 * 340 = 2720 Wh and my battery is 858 Wh

            3- does that mean that my battery endure more the 3 charging cycle (2720/858 = 3.2) at high rate on that day.

            at 20 kph, the motor ask for around 250 Watts. so if I produce 340 Watts there is 90 Watts free to recharge the battery.
            But
            because the whole 340 W goes through the battery, that the charging cycle must be calculated with the full 340 ?

            4- is that right ?

            As the battery get full, the charger start to produce less power. So when My battery is full, I get less energy from the solar panel
            I tried to feed the solar panel at the output of the battery to avoid this, but was not sure it could be done.
            the BMS of the battery do allow some charge in reverse (created by regenerative breaking) but I think It cannot handle too much energy.


            5- is there a way to get the full 340 Watts of power but still minimizing the impact on the battery life ?


            thank you all




            Comment


              #7
              Originally posted by VeloSolaire View Post
              Oh, where should I setup the cut off tension. I currently set it a 41 Volts,
              1- Should I put it higher ?
              The minimum is 14 x 2.5V = 35V, so 41V is just fine. The higher is the cut-off voltage, the longer will the battery last, but the capacity will reduce. Also you can practice not charging to 100% (4.2V/cell) to make the battery last longer.

              Comment


                #8
                Originally posted by thunderheart View Post
                The minimum is 14 x 2.5V = 35V, so 41V is just fine. The higher is the cut-off voltage, the longer will the battery last, but the capacity will reduce. Also you can practice not charging to 100% (4.2V/cell) to make the battery last longer.
                I kind of partially doing it because the Charger can only to 56.8 but the full battery 58.8. I did not do the math to see the V of each cell. let's try with my new knowledge.
                56.8/14 = 4.06
                so it is a little below 4.2
                4.05 / 4.2 = 96%.
                I dont know how to control my charge more than that


                thank you everybody for your answers.


                Comment


                • AZguy
                  AZguy commented
                  Editing a comment
                  You *must* charge to 100% every few cycles to ensure the cells get balanced
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