User Tools

Site Tools


electrical:severe_battery_use

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.
1)
“dead lead”
2)
as when the controller setpoint is maxxed out
3)
but still manufacturer-sanctioned
electrical/severe_battery_use.txt · Last modified: 2020/10/11 19:48 (external edit)