Morningstar Idle Battery Custom Settings
These “idle battery” charge settings are designed for off-grid or standby backup solar PV systems which can have extended periods with little or no-load usage. These settings were developed due to issues that some customers have had with their batteries getting overcharged when using the factory presets with an off-grid solar PV system that was mostly sitting idle for long periods of time. The presets for Morningstar controllers include Absorption time and slightly higher Float voltage settings. These settings were designed for and work well with lead acid battery systems which are generally cycled on a daily basis to some extent. Typically, off-grid solar systems are designed for at least 10% discharge/ day.
Options for batteries that are mostly sitting idle for long periods of time can be adjusted as follows
- Greatly reduce the daily Absorption Time allowing longer Absorption Extension Settings to take over if the battery voltage gets low.
- Use reduced Absorption and/or Float Voltages to prevent unnecessary charging.
- Reduced Temperature Compensation to reflect low current conditions of idle batteries.
- Disble Equalize with DIP Switch #7 Down/Off or Increase # of days for Auto Equalize interval
The downloadable configuration files include the factory presets which have been modified as follows.
- Daily Absorption Time is reduced to 5 minutes
- Absorption Extension Settings remain enabled with the Absorption Extension Voltage increased to 12.55V
- Float Voltages reduced to 13.4V
- Battery Temperature Compensation reduced to .02V/degC
- Increase # of days for Auto Equalize interval to 50 days in case it is enabled with DIP Switch #7 UP/ON
List of Morningstar product Factory Presets with Idle Battery Adjustments Config files.
Note that some settings such as Communications, Notifications and certain internal Data Log settings can be programmed independently of whether the controller is set to a Factory Preset or a Custom setting.
As with any battery charge settings, optimal performance may depend on adjustments that are based on many factors including battery bank size, average daily loads, battery temperatures and daily charge rates which depend on location specific criteria and array sizing. Cumulative Daily Absorption Time adjustments should be considered on a case by case basis.
IMPORTANT – These settings typically should not be implemented when the system is not sitting idle.
Adjustments should be made depending on operating parameters and the degree to which the battery remains idle.
An option is to use the DIP Switches to enable the required Factory Preset for normal operation and the Custom DIP Switch setting when the system is idle.