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LiFePO4: charging

[last updated: 2025-05-07]
battery - home page
LiFePO4 batteries
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  • Charging:
    • Recommended to use a charger designed for LiFePO4 batteries, "to avoid overcharging".
        A "balance charging board" is used to ensure that each cell in a multi-cell LiFePO4 battery pack is fully charged and that no cell is overcharged.
          Clueless how you're supposed to do that with a sealed multi-cell battery, with no access to the individual cells...

    • Initial charging at constant current of 0.3C. ("bulk charging")
      When the battery voltage (individual cell) reaches 3.65V, use 3.65V constant voltage charging. ("absorption charging")
      When the charging current is lower than 0.1C (or 0.05C), stop charging.
      • So for my Sefepoder battery listed above, this translates to:
        Constant current: (0.3 x 15 =) 4.5a until voltage reaches (3.65 x 4 =) 14.6v
        Constant voltage at 14.6v until current reaches (0.1 x 15 =) 1.5a, then done.

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    • My tests:
      • First Sefepoder 15Ahr:
        • Set up my Hammetek bench supply to do 4.5A as recommended. Worked for awhile, an hour+, but then shut down.
          That is, the bench supply just stopped its output, amps went to zero.
          Not sure if some shutdown circuit in the supply, or, my opinion at the moment, that some auto-shutdown circuit in the battery itself was activated.

        • Detailed log:
          Bottom line, max charge was 13.30V.

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      • Second Sefepoder 15Ahr:
        • Out of the box: 13.16V
        • Set up on bench at 1.0A for about an hour,
          then about 1/2 hr at 3.0A ...
          Stabilized at 13.30 after resting all day.
        • Charged again at 3.0A for about 2 hrs.
          Stabilized at 13.34 after resting overnight.

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    • Not sure about this...
        Chopper charging method: the current of the constant current source remains unchanged, and the switch tube is controlled so that it is turned on for a period of time and then turned off for a period of time, and the cycle repeats.
        The advantage of this method is that, during charging, the ion generation inside the battery requires a certain response time, and if it is continuously charged, it may reduce its capacity potential. After charging for a period of time, adding a turn-off time can allow the ions generated at the two poles of the battery to have a diffusion process, so that the battery has a “digestion” time, which will greatly increase the utilization rate of the battery and improve the efficiency of the battery. charging effect.

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  • from: https://www.redwaybattery.com/redway-batterys-lifepo4-batteries-tests-8-...
    • Fully Charge the Battery: Ensure the battery is fully charged according to manufacturer specifications.
    • Connect a Load: Use a resistive load or electronic load tester that can safely discharge the battery at a specified current (e.g., 0.2C).
    • Monitor Discharge: Record the time it takes for the battery voltage to drop to its cut-off voltage (usually around 3.0V per cell).
    • Calculate Capacity: Use the formula:
      Capacity Ah =Discharge Current A ×Time h
      For example, if you discharge at 10A for 5 hours, the capacity is 10A×5h=50Ah10A×5h=50Ah.

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  • Measure internal resistance:
    Typically should be 150 - 300 milliOhm
    https://harveypoweress.com/test-the-lifepo4-battery-internal-resistance/
    https://www.ufinebattery.com/blog/lithium-ion-battery-internal-resistance/
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