Many consumers and installers indicate that they do not adjust their solar charge controller’s absorption, float, and equalization settings according to the batteries that they are using. Hence they are using the controller’s factory presets, without realizing that this is most likely not optimal for the health and performance of the battery brand and type they are using in their application. While the charge controller will work and their off-grid PV system will function, they will likely incur one or more of the following consequences:
- Battery sulfation at the internal lead plates
- Low battery state of charge
- System downtime due to insufficient charging
- A significant reduction in overall battery operating life
- A decrease in overall storage capacity
In order to optimize battery health and performance it is recommended to contact your battery manufacturer and have them provide you with the precise recommended absorption, float, and equalization voltage including duration, and interval parameters that you can set for your charge controller. These parameters will vary depending on the battery brand, type and chemistry (e.g. sealed, gel, flooded lead acid, lithium, etc.). As an example, for a given battery, a manufacturer might recommend:
- absorption charge at 14.1V for 3 hours
- float charge at 13.7V for 2 hours
- equalization charge at 14.9V for 2 hours once per month
(note: this is an example and equalization is not recommended for some batteries)
It is not uncommon for batteries to last only a couple of years if charge controller settings are not set to battery manufacturer specifications. But, by following battery manufacturer recommended setpoints, some batteries can often last for 5 to 10 years or more. Since batteries are often the most expensive component of your off-grid system (representing 40% of initial costs and up to 80% of lifetime costs), adjusting charge settings is extremely important. Proper charge controller settings not only reduce lifetime battery costs, it also reduces the time and money you spend to replace the batteries and the costs associated with system downtime. Installers and consumers can find recommended charge settings on battery manufacturer websites, operation manuals, or by contacting them directly.
Controllers with interactive input displays
Metered versions of ProStar (Gen3) PWM and ProStar MPPT controllers, and the new GenStar MPPT controllers have interactive input displays with scroll buttons that allow for adjustments to absorption, float and equalization parameters within seconds directly at the controller, with no additional data connection needed. The key words are “interactive input” since some meters on TriStar controllers for example, only allow “read only” interaction, but not interactive input and adjustment of charge settings. In order to use the controller’s interactive meter to adjust the setpoints, you should ensure that DIP switches 4, 5, and 6 are in the ON position (indicating a custom setting), otherwise your meter screen will not display options for adjusting absorption, float or equalization charge settings.
Controllers without interactive meters
Morningstar controllers without interactive input meters, such as TriStar PWMs, TriStar MPPTs, non-metered ProStar PWMs and ProStar MPPTs, and SunSaver MPPT’s can use a PC and our free MSView software to adjust and program charge settings. See the MSView page for more info. If you would rather not use MSView, you can consult the solar controller’s operation manual to find DIP Switch settings that will establish a preset that most closely matches the recommended setting for your battery. Please note that a preset that is labeled and generally used for Sealed batteries can be used for other battery types, if the particular battery type’s recommended settings most closely match the labeled preset. It’s the numerical settings that are most important, not the labels.
Controllers with Battery Select Jumpers
Morningstar’s SunSaver PWM and SunLight PWM controllers have battery select jumpers. When inserted they set absorption voltages lower than when removed. The Battery Select Jumper is typically inserted for sealed batteries. Moreover, when jumpers are removed, this creates a higher absorption setpoint voltage and it also enables an equalization charge.
Other environmental factors can impact controller charge settings. Batteries that are located in off-grid applications that are exposed to cold temperatures for long periods of time might require higher voltage settings, whereas hot temperature exposure might require lower voltages. Fortunately, many Morningstar controllers have built-in temperature compensation and others can use a remote temperature sensor to account for the effects of temperature.
Load consumption and battery depth of discharge are also factors. Systems that experience consistent small load consumption and low battery depth of discharge throughout the year generally require lower voltage settings than systems that experience inconsistent load consumption or greater depth of discharge. While there might be some differences of opinion on optimal charge settings for a given system, these differences are small when compared to doing nothing at all.