Update: Choosing a GoPiGo3 Safety Shutdown Voltage for the ModRobotics Battery Pack

GoPiGo
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Back in June I was designing ROSbot Dave’s safetyShutdown.py battery charge monitor and chose:

  • WARNING: (Flash WiFi LED Orange) 10v
  • SAFETY SHUTDOWN: 9.75v
    • write session duration and final battery voltage to log
    • initiate shutdown -h

I just ran an unprotected discharge to battery cutoff which confirms 10v warning flasher:

  • starts 30 minutes before total battery exhaustion,
  • ~15 minutes before chosen safety shutdown at 9.75v

 

Latest Run:

Full Charge 12.5v (open circuit) to

      Battery Protection Circuit Shutoff at 8.5v (under load)

BatteryDischargeCurve_2599mAh_5.6hrs
BatteryDischargeCurve_2599mAh_5.6hrs1077×885 60.2 KB

This run was 2599mAh in 5.6 hours = 464mA average load

It shows I am shutting down at 5% remaining battery capacity.

This level of discharge might be stressing the battery cycle life - we’ll see. At this point the battery has about a 100 sessions of an average 1.3 hours each in 1.5 months. I don’t always charge it after a session though - only if the voltage is below about 10.5v will I put it to charge. Internet wisdom recommends Li-Ion batteries should not be “stored” fully charged or fully discharged. Dave is only “stored” 18 hours at a time, max.

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I would suggest 10v as the drop-dead voltage, or at least as Vwarn to stay away from the knee of the curve.

I have not seen any recent data about the number of cycles vs depth of discharge. What I have seen is cycles vs charge current, (the lower the better)

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