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Why does it take 2hours to fully charge?

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  • Why does it take 2hours to fully charge?

    A quote from sunking from the thread titled Victron charge controllers for lifepo4
    Take a fully discharged 100 AH cell, charge at 1c and it wil take you two hours to recharge to 3.6 volts @ .03 finnish current. At 1C you wil hit Absorb when the battery is roughly 60% SOC, or about 30 to 40 minutes into the charge cycle. From there another 1 to 1.5 hours to Absorb to 100%.
    As I understand 1C means 100AH divided by 1=100amps, or time to discharge the battery in one hour would be 100amps.
    If 1C is 100Amp charge rate how come it takes 2hours? Shouldn't it be just 1hour?

    I have also read the same about the times on other sites & wondering why can't you fully charge in say 30mins or just 1hour?

    cheers

  • #2
    The battery will not continue to accept a full charge rate to get to 100% SOC. It will go through stages and only accept a smaller charge rate until it gets to full Absorb condition. That takes more time. Think of it as an internal safety to keep a battery from overcharging as well as overheating.

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    • #3
      In a nutshell, it's chemistry / physics. As the battery "gets more full" internal resistance increases (electrons get crowded, temperatures rise, tempers flare) d your battery charger has to shout louder and push harder to get anyone to listen (-: I like to think of Japanese "train pushers" (www).youtube.com/watch?v=pYefhPALCpU

      You can always charge faster and harder by increasing the driving voltage and current to partially overcome the increase in internal resistance. But eventually you will let the magic smoke escape and then she won't charge no more. Just be sure to try that experiment outside and have the correct class of fire extinguisher standing by.

      But if you want your batteries to last as long as possible, you want to discharge and charge them slowly, limit the depth of discharge, and thermally monitor/regulate them throughout.

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      • #4
        Originally posted by JSchnee21 View Post
        In a nutshell, it's chemistry / physics. As the battery "gets more full" internal resistance increases (electrons get crowded, temperatures rise, tempers flare) d your battery charger has to shout louder and push harder to get anyone to listen (-: I like to think of Japanese "train pushers" (www).youtube.com/watch?v=pYefhPALCpU

        You can always charge faster and harder by increasing the driving voltage and current to partially overcome the increase in internal resistance. But eventually you will let the magic smoke escape and then she won't charge no more. Just be sure to try that experiment outside and have the correct class of fire extinguisher standing by.

        But if you want your batteries to last as long as possible, you want to discharge and charge them slowly, limit the depth of discharge, and thermally monitor/regulate them throughout.
        Thanks


        Well I just assumed the tapering of current was right at the end & insignificant. So to me another one of the handful of reasons why lithium is not as good as the hype makes it out to be. especially for causal use like RV & base camping. Cheers all.

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        • #5
          Originally posted by Jman View Post

          Thanks


          Well I just assumed the tapering of current was right at the end & insignificant. So to me another one of the handful of reasons why lithium is not as good as the hype makes it out to be. especially for causal use like RV & base camping. Cheers all.
          As far as I know all battery chemistries follow the same rule of tapering off their charge rate at some point in the process. The time and amount differs but there is still a delay to get to 100% SOC.

          Again it has to do with internal resistance of the battery and the laws of physics.

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          • #6
            Originally posted by SunEagle View Post

            As far as I know all battery chemistries follow the same rule of tapering off their charge rate at some point in the process. The time and amount differs but there is still a delay to get to 100% SOC.

            Again it has to do with internal resistance of the battery and the laws of physics.
            Thanks

            I recall reading stuff about Lifepo4:
            - that absorption is almost non existent (15-30mins) if target voltage is high. (perhaps true but they don't mention the life shortening doing this)
            -lifepo4 can take almost all what the alternator can delivery right up to full (this was about how lithium taxes the hell out of the alternator)

            source of my confusion.

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