SERIES CHARGE CONTROLLERS – Connected between the charging source and the battery. Pulse width modulation (PWM), used in all modern charge controllers uses 3-stages of operation to give the most charging possible for the day.
BULK charge is the first stage, where the maximum power available from the charging source is fed to the battery until it reaches a preset voltage.
ABSORPTION is the second stage charge where the maximum battery voltage is held by reducing the charge current just enough to never exceed the target voltage. Reduced current is done by high speed on and off pulsing, where the controlling "on" time versus the "off" time of each pulse determines the average charge current. During this stage of charging there will be some bubbling, or gassing of the battery electrolyte. This is necessary to maintain the health of flooded batteries.
FLOAT is a third stage where battery voltage is reduced after charge is complete. This avoids excessive evaporating of battery water and benefits battery life. When sealed, maintenance-free, AGM or gel type batteries are used, voltage set-points are lower to prevent gassing of the battery.