PWM charge controllers

This type of controller, which uses pulse-width modulation, can only be used in 12 volt 36-cell or 24 volt 72-cell panels.
These are controllers that operate on the voltage of the battery, irrespective of the voltage produced by the solar panels.

This means that when the voltage produced by the panels is higher than that of the battery, it is wasted. In other words, the energy generated by the panels is not used to its full potential.

These controllers are designed for small, low power installations. Their main advantage is the lower price.