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Basic Function

The basic functions of a controller are quite simple, they prevent battery overcharge and block reverse current to prevent electrical current from flowing out of the batteries.

Overcharging batteries will at the least significantly reduce battery life and at worst damage the batteries to the point that they are unusable.

A charge controller is needed in virtually all solar power systems that utilize batteries. While the basic function of a charge controller is simple they might well be the most complicated part of the whole solar electric system.

Different Types

There are different types of controllers,  basic charge controllers are very simple on or off systems.  Pulse width modulation (PWM) and maximum power point tracker (MPPT) technologies are more electronically sophisticated, adjusting charging rates depending on the battery’s level, to allow charging closer to its maximum capacity.

How They Work

A simple or basic charge controller simply monitors the battery voltage stopping the charging when the battery voltage rises to a certain level, and restarting when it drops to a certain level. Inexpensive but they are inefficient and old technology.

The more modern PWM charge controllers are a type of charge controller that slowly reduces the charging current to avoid overheating the battery after it has reached the regulation setpoint.

At the same time, the system continues to send the highest amount of energy over the shortest period of time , which results in rapid charge and high efficiency.

This type of controller allows the batteries to be more fully charged with less stress on the battery, extending battery life. It can also keep batteries in a fully charged state (called “float”) indefinitely.

MPPT is the top of the line charge controller in the market. The MPPT is a high frequency converter that takes the DC input from the solar panels, changes it to high frequency AC, and converts it back down to a different DC voltage and current to exactly match the panels to the batteries.

It tracks the input power from your solar array and the voltage from your battery bank and adjusts the voltage for the highest amp output to the battery bank.

PWM And Mppt Chargers

The Mppt controller is capable of taking a higher voltage and ‘down converting’ it to a lower voltage while ‘up converting’ the amps.  Simply put, say your solar panels have an output of 24 volts and 5 amps and your battery bank is at 12 volts.

The Mppt will ‘down convert’ the voltage from 24V to12V and while doing this it will ‘up convert’ the amps to 10 amps. So you would have 12 volts and 10 amps to the batteries resulting in a more efficient system.

The PWM controller using the same system will take the higher voltage and ‘down convert’ it to a lower voltage but there is no up converting. So a simple way to look at it is you lose half the volts and half the amps, remember that the Mppt controller uses these down converted volts to double the amps.

MPPT charge controllers offer a potential increase in charging efficiency up to 30 % but of course they are much more expensive. Both systems work well but even at the higher cost MPPT charge controllers are best for your system.