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Initial charge with less than 0.1c?

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  • Initial charge with less than 0.1c?

    Hi. I have plans to make a small solar off grid generator. I bought 4 130Ah Winston cells and l am trying to do initial charge with a 3.65v 15A charger. I connected the cells in parallel and they have been charging now for approximately 48 hours. Voltage has only risen from 3.28>3.35 during that time. Since the combined Ah of cells is 520 15A is only 0.028 C. Also I think the charger does not give constant current of 15a. My question is that am i doing damage to the cells by trying to charge them with low C rating? Would it be better to connect them in series and let my 280w solar panel and mppt charge controller to charge the pack to 14.6v (3.65v per cell) before i do bottom balancing?

  • #2
    No such thing as charging lithium batteries too slowly. If you are going to Bottom Balance, WHY are you charging to 3.65 volts? That is not Bottom Balance, that is Top Balance.

    If you intend to Bottom Balance, turn the charger off. To Bottom Balance you connect the cells in Parallel, However you do not charge them, you discharge them to 2.5 volts. You are Top Balancing.


    MSEE, PE

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    • #3
      Thanks for answer. I was thinking that if charge takes many days and cells are at high voltage for long time it causes damage. After this initial charge i intend to bottom balance. How ever i wonder is it necessary to go as low as 2.5v. i am thinking i would bottom balance around 2.7 or 2.8

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      • #4
        Originally posted by Turponieminen View Post
        Thanks for answer. I was thinking that if charge takes many days and cells are at high voltage for long time it causes damage. After this initial charge i intend to bottom balance. How ever i wonder is it necessary to go as low as 2.5v. i am thinking i would bottom balance around 2.7 or 2.8
        To be most effective, bottom balancing should be done at a voltage lower than you intend to reach during normal use. That way you are most confident that in a series circuit no cell will go below the minimum allowed voltage before the entire string trips the low voltage cutoff.
        SunnyBoy 3000 US, 18 BP Solar 175B panels.

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        • #5
          Originally posted by inetdog View Post

          To be most effective, bottom balancing should be done at a voltage lower than you intend to reach during normal use. That way you are most confident that in a series circuit no cell will go below the minimum allowed voltage before the entire string trips the low voltage cutoff.
          Yes, i plan to stay above 2,9v per cell.

          Got the cells charged btw. I disconnected the charger at 3.36v. Last evening. This morning i started to charge again and in few hours voltage had risen to 3.40, again couple of hours and it was 3.50, another two hours and cells are now 3.65v.
          I guess the charge curve of lifepo cells is so flat at 3.33-3.36 volts that it took 48 hours, and from 3.36 to 3.65 only 12 hours or so. Can't really determine SOC from voltage with these if it is near 3.3 volts

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