Charge Controllers

What does a charge controller do?

A charge controller is placed between the solar panels and the battery to charge the battery at the correct voltage and current and to protect it against overcharging and over-discharging. When a panel is connected directly to a battery, the battery can overcharge, shortening its life or causing damage. The controller also prevents the battery from discharging back through the panel at night, and many models offer a load output and status indicators.

The difference between MPPT and PWM

• PWM controllers: Operate by reducing the panel voltage to the battery voltage; an economical solution for small systems where panel and battery voltages are close to each other.
• MPPT controllers: Continuously track the panel's maximum power point and convert the excess voltage into current; they deliver more energy especially when the panel voltage is higher than the battery voltage.

The category includes 10 A PWM and 20 A MPPT models.

Selection criteria

The current rating of the controller must cover the maximum current the panels can produce with a safe margin. For MPPT controllers, the open-circuit voltage of the panel array must never exceed the controller's maximum input voltage under any conditions; this margin is important because panel voltage rises in cold weather. The battery type (gel, AGM, flooded, or lithium) must be set correctly on the controller; an incorrect setting shortens battery life.

Installation sequence

For most controllers, it is recommended to connect the battery first and then the panels; removal is done in reverse order. The connection sequence is also specified in the manufacturer's instructions. The controller should be mounted close to the battery in a ventilated location not exposed to battery gases. Appropriate cable sizes and fuses must be used.

Frequently asked questions

How much more energy does an MPPT controller provide?

The gain depends on the difference between the panel and battery voltages, the temperature, and the solar conditions.

What current rating should I choose?

It is selected by adding a safe margin to the total short-circuit current of the panels.

Can it be used with a lithium battery?

Models with a lithium battery setting can be used; check the product specifications.

What does the load output do?

It directly powers small DC loads such as lighting and disconnects the load when the battery is depleted.

Can a panel be connected directly to a battery?

It should not be; a controller is essential to protect the battery.

Where should I look for battery selection?

Browse the solar gel batteries category for suitable batteries.