Lithium Battery Charging

[last updated: 2022-09-01]
Li-ion batteries
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• Charging Boards:
  • Adafruit MCP73833 charger (ADA: 259)
    
    
    
    • It has 3 LED's onboard:
      red for power applied to the board
      yellow for charging in progress
      green for charging completed

    • Charging problems:
      • If both yel & grn LED's are on, it suggests the battery is defective (has been discharged too low)
      • I bought 20@ 5300 mAh 18650's in 2017. I used some of them, but most of them not. So in Sep-2020 I decided to check their charge level and charge them.
        Several still had 3.2+ volts and charged completely (ADA:259).
        One only had 1v or so ...
      • 4 of them had been built into a 20,000 mAh pack. I put it on a USB port to charge, and it started with still having 3 of 4 bars charged...

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  • DDTCCRUB:
    
    
    
    
    

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• Info from Brian Jenkins:
  • Charging LiPo batteries starts in constant Current mode, then switches to constant Voltage mode when the battery reaches a threshold voltage.
  • Constand current rate (in ma) is 1/2 the mah capacity rating of the battery.
  • Constant voltage rate will be max rating of the battery:
    "We are charging 4 batteries in series, so 4 * 4.2v = 16.8v is our maximum charge voltage."
  • Constant current circuit:
    Uses LM317
    Current cal resistor:
    R_cal = 1.25v / (charge current in amps)
    Power-rating-of-R = 1.25v * (charge current in amps)
  • Constant voltage circuit:
    Also uses LM317
  • Programming:
    Arduino monitors voltage and current
    Has two output relays to switch the two charging circuits on or off (constant current & constant voltage)
    Charging starts in CC, then switches to CV when voltage reaches 80% of target.
    Charging is complete when CV charging drops below 50ma.
    Additional programming might monitor battery temperature and stop charging if it gets too hot,
    or perhaps disconnect a load if battery voltage depletes too much.

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