Charge controllers are solid-state electronic devices used in nearly every solar energy system that uses batteries.

A charge controller is used in solar systems with 12 volt to 48 volt battery banks to keep the voltage to the batteries within acceptable limits.

A charge controller automatically stops electrical power when systems batteries become fully charged.

PWM charge controller capacities range from 4 to 80 A and multiple charge controllers can be used in parallel for larger solar battery system.

PWM simply means pulsewidth modulatio.

The Pulse width modulated (PWM) charge controllers turn on and off very rapidly, maintaining the batteries at full charge with whatever power is available.

PWM charge controllers regulate the charge of the battery, but also prevent the battery from being over discharged which can damage the battery bank.

PWM charge controllers have multiple stages of control it uses to regulate different voltage and current levels.

The voltage and current of a battery varies over the different stages of battery charge.

Though the amount can vary, the bulk charge usually is approximately 80%, the absorption charge is 10% with the float charge representing the balance of the battery charging process. The bulk charging stage of the charge controllers process is the first stage used to bring the battery depth of discharge (DOD) back to 100%.

The bulk charge stage happens first in in the morning after the batteries DOD has drained down since sunset the previous day.

The bulk charging stage pushes as many amps into the battery bank as possible from the solar panels and gets the voltage up in the process. The effect of a charge controller is like trying to fill a glass of water from a tap. You first turn the tap on full while the glass if filling, then slowly reduce the pressure until the glass is full.

When the battery bank reaches a predetermined level known as the bulk voltage set-point, the charge is then substantially slowed. Because the bulk voltage set point is determined by the type of battery you are using, many PWM charge controllers have to be pre-set to the type of battery which will dictate the rate of charge.

The second state of charge the PWM charge controller employs is the absorption stage.

After a battery system has been brought up to the bulk voltage set point, the charge controller slows down the charge rate because the battery bank cannot accept the same rapid charging pace without overheating and damaging the battery bank.

At the absorption stage a battery bank is only about 80% full. The absorption charge is the function level in the process that tops off the battery bank. During the absorption stage, the PWM charge controller holds the battery volts constant and reduces the amount of current sent into the battery. When the absorption stage is complete, the battery bank is fully charges.

The final step PWM charge controller performs is the float charge. Typically a charge controller enters into a float charge state when the other charge levels of the battery bank has been achieved.

When the number of peak sun hours is limited, a PWM solar charge controller may not be able to get the battery bank back to the float stage before the next cycle begins.

We recommend the MPPT solar charge controller because it is better and more efficient than PWM.