Maximum power point tracking is used to charge the batteries with the highest current possible, but this is only part of the equation. A battery cannot be charged at maximum power all the time for safety reasons, so multiple stages are used.
These stages include: bulk, absorption, float and, for some types of batteries, equalization as indicated below.
STAGE 1: BULK
In quick charge stage, the battery voltage has not yet reached the set value of full charge voltage (i.e. equalizing/boost charge voltage) and the controller will perform MPPT charging, which will provide maximum solar energy to charge the
battery. When the battery voltage reaches the pre-set value, Stage 2 charge will start.
STAGE 2: ABSORPTION
When the battery voltage reaches the absorption voltage, the controller will perform constant voltage charging. This is no longer MPPT charging, and the charging current will gradually decrease with time.
STAGE 3: FLOAT
Float charge is conducted following the absorption charge stage. The controller will reduce the charge current to a small amount in order to reduce sulfates on the battery plates or to allow a lithium battery to balance it’s cells. If the load
exceeds this small current the battery voltage will start to decrease until it reaches the recharge voltage. When the battery voltage falls below the recharge voltage, the controller will switch back to bulk charging.
STAGE 4: EQUALIZE
Warning: Risk of explosion!
Equalizing vented lead-acid battery may generate explosive gases. So, the battery compartment must be well ventilated.
Caution: Damage of device!
Equalization can increase the battery voltage to levels that may damage sensitive DC loads. It is necessary to verify that the allowable input voltage of all system loads is greater than the equalizing charge set value.
Caution: Damage of device!
Over charge and excessive gas evolution may damage the battery plates and cause active substances on the battery plate to come off. Equalizing charge may cause damage if voltage is too high or time is too long. Please carefully check the specific requirements of battery used in the system.
Certain battery types benefit from regular equalizing charge, which can stir electrolytes, balance battery voltage, and complete the chemical reaction. The equalize charge increases the battery voltage above a standard voltage, causing
vaporization of battery electrolyte. By default, this happens every 30 days for flooded batteries.
After the battery is completely charged the charging cycle completes and the battery is allowed to slowly discharge until it reaches the charge return voltage at which point a new charge cycle is initiated.
CHARGE PARAMETERS FOR VARIOUS BATTERY TYPES