how to adjust DoD when LVD is preconfigured in most charge controllers??

Re: how to adjust DoD when LVD is preconfigured in most charge controllers??

Welcome to the problem of managing a battery bank... The voltage on the battery is the results of many different active process variables (temperature, electrolyte, dynamic mixing of electrolyte, value of current, etc.). Even measuring electrolyte specific gravity can be affected by stratification (dense acid sinks, light mostly water floats, takes time and/or bubbles to mix electrolyte from next to the plates into the balance of the electrolyte "bath", etc.). You can estimate the specific gravity by measuring the "resting voltage" of the battery (~3 or more hours of no charge/discharge current flow).

Plus, depending on the brand and intended market for a battery, the initial S.G. can be "adjusted" (lower S.G. levels for standby/long life; higher S.G. for more capacity, better cycling capacity).

Resting Voltage

Typically, when a battery is first subjected to a high current low, the battery voltage will quickly depress, then pick up again a bit.

Some of the LVD circuits will lower the LVD cutoff voltage for heavier current flows.

Some battery manufacturers will give you a charge relating S.G. and Resting Voltage to State of Charge--otherwise you just use a generic table.

If you are looking for a "better way" to manage your battery... Take a loot at Battery Monitors (Victron Energy, Smart Gauge Website, etc.).

Basically, you install a precision resistor (current shunt) in the negative lead of the battery. The meter measures the current flow through the 500 amp resistor (voltage drop), totalizes the current flow * time (Amp*Hour), and runs it against an internal model (taking voltage, temperature, and such into account).

Sort of the equivalent of placing a fuel flow meter on the fuel line to your gas tank and monitoring fuel use (discharge) and fuel replenishment (recharging) to estimate what is in the fuel tank (aka Gas Gauge).

These meters will display your state of charge 0-100%, or in Amp*Hours, and display other parameters.

A few (some Xantrex and Victron units, at least) will allow you to set an alarm contact to turn "on" at 50% and turn "off" at 80% state of charge--you can use this as a human alarm or as a signal to start a genset, bother the teenagers, etc...

They are not perfect (they estimate batter state of charge, and typically "reset" back to 100% when they see battery voltage at 14.5 volts, low charging current, for a period of time--for example). Battery Monitors are very handy for AGM and other sealed batteries where you cannot measure specific gravity.

Anyway, another option...

-Bill