A Few Observations on Battery Performance

This post is going to deviate a little bit from my typically long-winded format and present a list of observations and measurements so far.  In short, I’m very pleased:

  • The charger charges at a constant rate until it reaches the upper voltage shutoff
  • After shutting off the charger, voltage drops by less than 0.2V  (in 48) over the next several hours with no load.  This suggests that the surface charge effect is small.
  • When the charger is on, there’s no immediate spike in battery voltage.  Turning the charger on/off only influences the voltage by about 0.1V, meaning that even if it is on, we can still use voltage as an indicator of state of charge.
  • At each of several measurements, all cell voltages stayed within 0.01V of each other.
  • The self-discharge rate is (for all practical purposes) zero.  After 2.5 months in storage, the voltage was unchanged.
  • Charging or discharging a 4kW module at 1500W results in no noticeable heating of the battery pack, cables, or connectors.

Coming soon (not necessarily in this order):

  • Overall system objectives
  • Discussion of battery management/monitoring systems
  • High and low voltage disconnects
  • Over- and under-temperature disconnects

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