Table of Contents

Solar charge controller setpoints

Solar charge controller, converter, and DC-DC charging behavior is guided by setpoints, which are settings stored in the controller. They may or may not be configurable by the user.

The two most important setpoints for battery life and performance are charging voltages: Absorption voltage and Float voltage, discussed below.

charging setpoints

Charging setpoints are configured in accordance with the battery manufacturer's recommendations.1) These recommendations are published in manuals, spec sheets, corporate blogs, etc. For example, Trojan's recommendations for charging their T-105 AGM batteries looks like this:

Simpler charge controllers may only have preconfigured presets like “FLOODED” or “AGM” and don't let you set exact setpoints. If this is the case pick the closest preset to the recommendations5) and understand you will likely not get full performance or lifetime from the battery bank. Shunt controllers typically have only one configurable voltage setpoint. The simplest controllers may have no battery settings at all, and may or may not publish what those mystery settings are.

Less common setpoints:

load setpoints

Only present on controllers with LOAD outputs.

non-setpoint settings

1)
Learn 'em, live 'em, love'em!
2)
sometimes confusingly called “boost” stage
3)
the controller being in Float does not necessarily mean the batteries were fully charged; controllers can drop to Float too early due to bad design, incorrect battery chemistry switches, or incorrectly-configured setpoints.
4)
actually C/20/200, but C/200 here for simplicity
5)
using Price Is Right rules: closest without going over
6)
or whatever
7)
lead batteries accept what they want rather than taking what they are given