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Solar charge controller setpoints
Controller behavior is guided by setpoints, or values stored internally. On simpler controllers the setpoints may not be adjustable. On others there is a range of values that can be stored.
charging setpoints
Charging setpoints are configured in accordance with the battery manufacturer's recommendations. These are often found in manuals and spec sheets. For example, Trojan's recommendations for charging their T-105 AGM batteries looks like this:
Simpler charge controllers 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 recommendations1) and understand you will likely not get full performance or lifetime from the battery bank.
Absorption voltage (Vabs) - the voltage the battery bank is held at during
Absorption stage. In this case the recommendation is 14.4v.
Float voltage (Vfloat) - the voltage the battery bank is held at during
Float. In this case the recommendation is 13.5v.
Maximum charge rate: While maximum charge rates normally are immaterial to solar charging, Trojan specfies a maximum of
C/5, or 1/5th of the battery's capacity in Ah.
Minimum charge rate: not stated in our example, but typical minimum charging values are ~C/10 for lead chemistries.
Temperature compensation - how the voltage setpoints are adjusted for temperature. While this is sometimes configurable, generally the compensation factor is close enough between manufacturers that it can be left at the default.
Absorption termination - the amount of current (or percentage of capacity) accepted by the battery in late Absorption that indicates it's appropriate to Float. In the lower-right of
this graph Trojan shows it as
C/200:
2)
Less common setpoints:
Absorption duration - the amount of time Vabs will be held until dropping to Vfloat. Somewhat common.
Absorption restart - voltage (or duration) at which Absorption stage after failing to maintain Vfloat
load setpoints
Only present on controllers with LOAD outputs.