A solar charge controller keeps a battery bank from overcharging and turns off solar panels at night to block current from reversing from the batteries to the panels, an important function since electrons can flow both ways. Learn more about how charge controllers work and how they add to battery life.

Charge Controller

Solar charge controllers were created with two distinct and important purposes:

1. They keep a battery bank from overcharging.
2. They turn off the solar panels at night to block current from reversing from the batteries to the panels, a

In practical terms, charge controllers are important because if you hook a solar array directly to a battery without the overcharge protection a controller provides, you’ll boil the battery dry and ruin it.

significant function since electrons can flow both ways.

How Charge Controllers Add to Battery Life

Early charge controllers contained a simple relay that opened at a pre-set high voltage and closed at a pre-set lower voltage, allowing the panels to resume charging the battery. Battery life was of no apparent concern as there was no way to properly fully charge a battery bank.

Nowadays, almost any charger can get a battery to 80% (Bulk) charge. The trick is charging the next 20% (Absorb). In the bulk mode there are variable voltages and all the available (constant) current (amps). When a pre-programed voltage setting is reached, the charger passes off to the Absorb mode (and timer).

The Absorb mode and timer uses constant voltage and variable (tapering down) current (amps) for a pre-determined period of time (Absorb time). This is the most important mode as this is the one that gets the batteries to full charge. Batteries must, for the health of the battery, come to a full charge at least every ten days.

Many charge controllers cannot be programed, rendering them useless for battery health and long life. Many people think the charge controller has some intelligence that senses the batteries and take care of the Absorb time. The reality is the charge controller manufacturer has no idea how many watts of solar you have and what batteries you bought. It is a mathematical computation and must be programed into the controller.

Everyone wants a less expensive charge controller, but you might save a few bucks on the controller only to end up spending a small fortune replacing batteries.

Next, see "How Big of a Charge Controller Do I Need?

Learn more about solar charge controllers here or call us at 888-826-0939 with any questions.