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Note: this is for deep cycle lead chemistries only.! Lithium chemistries should not be held at full voltage.

dealing with insufficient Absorption

In off-grid solar charging scenarios batteries are most often damaged by chronic undercharging. Specifically, not holding the manufacturer's recomended Absorption voltage (Vabs), and not holding that voltage long enough1) for acceptance to drop to endAmps.

Causes of insufficient Absorption:

  • configuration error - controller set to an insufficient duration
  • controller limitation - max duration is insufficient. Example: Tracer-style controllers typically have a 3-hr max.
  • solar conditions - not enough good sun long enough to finish Absorption

set Vfloat to Vabs

The Eternal Absorption approach completely forgoes Float stage, forcing the controller to stay in Absorption by setting Vfloat to Vabs. This addresses the controller issues above. It will not address the insolation problem on a given day, but extended Absorption will help reduce damage from previous days of poor harvest.

side benefits

PWM (and shunt) controllers make more power from panels when battery voltage (Vbatt) is higher.

Eternal Absorption may make timing opportunity loads simpler.


  • increased Vabs duration will require more frequent watering, due to increased outgassing
electrical/12v/eternal_absorption.1594224614.txt.gz · Last modified: 2020/10/11 19:48 (external edit)