Thursday, January 14, 2016

Recovering a Dead LiPo battery from "Low Voltage" with an IMAX B6AC battery charger

I was able to bring Big B's dead-dead LiPo Battery pack back to life.  Here's how.

We were out flying on New Years and Big B sent his shiny new Super Sky Surfer into the top of a particularly gnarly walnut tree. We got it down last weekend, but after a week the LiPo in it was stone dead.  His charger threw a Low Voltage alarm and wouldn't charge it.

Normally we charge these in LiPo Balance mode.  This won't work with a dead battery.  The trick is to slowly charge the battery at a low level to get it where the LiPo balance will work.  To do this I...
  • Place the battery in a fire resistant container, just in case.
  • Place the Battery charger in constant current (NiMH) Charging mode.
  • Set the current limit to 0.1 Amp.
  • Start charging:
    • Watch for any sign of battery failure.
    • Do not leave the charging battery unattended.
  • Charge the pack until it reaches a voltage that is acceptable to the balance charger.
    • I used 10 volts, i.e. 3.3 volts times the number of cells.
      • 1s = 3.3 volts
      • 2s = 6.6 volts
      • 3s = 9.9 volts
      • 4s = 13.2 volts
      • Ns = N * 3.3 volts, where N is the number of cells.
  • Stop charging.
  • Check to make sure the battery is not hot.  If it is, let it cool.
  • Switch the charger to Li-Po Balance Charge:
    • I don't want a fire on my desk, so I limited the Balance charge to 0.1 Amp to prevent overheating.
  • Start Balance Charging.
    • Do not leave the charging battery unattended
  • The charger should stop automatically.
My charger stops after 2 hours whether the battery is charged or not.  It was cool the whole time, so after it shut off I restarted the Balance Charge with a current limit of 0.2 amps.  After a half hour it was still cool to the touch, so I upped it to 0.5 Amps.  That ran for 2 hours and got it up to 11.6 volts.  I upped the charging current to 1 amp, and 30 minutes later Beep-Beep!  It's done!


This worked for me; I hope it works for you.

Hat tip to Youtube user NOTEB00KPC for this idea!

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