October 21
st
, 2021 40
Batteries
Battery Charging Information
4-Stage Charging
The MPPT has a 4-stage battery charging algorithm for rapid, efficient, and safe battery charging. The figure
below shows the stage sequence.
Bulk Charge Stage
In the Bulk Charge stage, the battery is not
at a 100% state of charge and has not yet
reached the Absorption voltage setpoint.
The controller will deliver 100% of available
solar power to recharge the battery.
Absorption Stage
When the battery has reached the
absorption voltage setpoint, we use
constant-voltage regulation to maintain
battery voltage at the absorption setpoint, preventing heating and excessive battery gassing. The battery is
allowed to come to a full state of charge at the absorption voltage setpoint. Absorption lasts until batteries
charge at 2% of the programmed Ah size.
Float Stage
After the Absorption stage charges the battery fully, the MPPT reduces the battery voltage to the float voltage
setpoint. If batts have 100% charge, there can be no more chemical reactions, and all the charging current
turns into heat and gassing. The float stage provides a meager rate of maintenance charging while reducing
the heating and gassing of a fully charged battery. The purpose of float is to protect the battery from long-term
overcharge.
Battery Charging Setpoint Examples (48V)
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