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Intentionally severe battery use

Lead-acid chemistries prefer light cycling and full recharge between those cycles. Lead-acid batteries are traditional cycled to 50% depth of discharge because it offers a balance between duty life (years between failure) and bank size.1) Pulling the bank below 50% DoD in emergnecies will not automatically cause damage assuming a full charge is accomplished ASAP.

This article is about the intentional severe use of lead-acid banks by running them below the 50% mark, followed by vigorous recharging at maximal voltage. This might be desirable when:

  • reducing the weight impact of lead banks
  • one wants to make use of old/damaged batteries whose capacity has declined

how low can we go?

For folks willing to trade battery longevity for some amount of increased capacity, common low-end targets for low voltage disconnect are:

  • 60% DoD / 40% SoC, ~12.0 rested volts
  • 75% DoD / 25% SoC, ~11.7 rested volts
  • 80% DoD / 20% SoC, ~11.6 rested volts

limiting the damage

  • get power back into the battery ASAP after deep discharge; drive for alternator charging or run a generator to get bulk stage going. Solar alone might be sufficient but it might require meaningful overpaneling.
  • fully charge lead-chemistry batteries as often as possible

increasing effective Absorption duration

Deep cycling generally extends the amount of time for a battery to complete Absorption. At some you may run into the controller's maximum Absorption duration. While you may not be able to increase the actual duration,2) you can achieve a similar effect with one or more of these techniques:

  • if duration setpoint is maxxed then set Vfloat == Vabs. Absorption duration will effectively be “until the sun goes down”.
  • charge at a lower current (charging minimum). While overall charging will take about the same amount of time, Bulk's share of that time will increase and Absorption will take somewhat less time.
  • Absorb at a higher3) voltage (Vabs), this will decrease Absorption duration. Keep a close watch on water levels for flooded batts, and also mind the max allowable voltage for AGM/Gel.
  • supplement solar charging with another charging source during Bulk, allowing more time for solar to finish absorption.
“dead lead”
as when the controller setpoint is maxxed out
but still manufacturer-sanctioned
electrical/severe_battery_use.txt · Last modified: 2020/10/11 19:48 (external edit)