Charge Controllers

Solar charge controllers, also know as regulators play a vital role in a solar system. The primary function of the controller is to regulate the voltage from the solar panel down to an optimum level to successfully and safely charge a battery (usually between 14.0 and 14.5 volts depending on the battery type). Without a charge controller the raw solar panel output voltage (~17 – 21V) would be too high for a 12 volt battery leading to overcharge, gassing and eventual failure. There is a caveat to this, for small solar panels a charge controller may not be required because the maximum voltage generated by the panel would not be sufficient to overcharge a 12 volt battery. However, always check with the supplier.

There are two main types of controller on the market – Pulse Width Modulation (PWM) and Maximum Power Point Tracking (MPPT) controllers. PWM controllers are the simplest and cheapest type and by far are the most common type used in recreational solar applications. Whereas MPPT controllers use a more complex algorithm to charge batteries, recovering up to 30% more power (some manufacturers claim) from a solar panel at any given instant. Consequently they are typically 2-3 times more expensive than PWM controllers.

We offer both types, as the cost of MPPT controllers has dropped, makng them a more affordable option for users to consider. However they are not recommended for all applications and the extra cost is often not justified in terms of extra performance. In those cases, inexpensive PWM controllers are the most suitable option.

If you are technically minded and want to know more about how controllers work, then read on. Alternatively, read our FAQ page on charge controllers which addresses common questions.

Pulse Width Modulation

A PWM controller continuously checks the battery state of charge and self adjusts or regulates only the right amount of charge (current) coming from the solar panel. The controller regulates how long and how frequent the pulses from the solar panel come. These pulses could best be described as a rapid on/off switching of current from the panel. When a battery is in a discharged state the pulses would be longer and more continuous. As the battery becomes more charged the pulses would become shorter and more infrequent, a so called ‘trickle’ charge. Think of it like filling an empty bucket with water, initially you want the flow to be high but as the level nears the top you reduce the flow until the bucket is completely full (and not overfilled).

Look for good quality 3-stage PWM controller as a minimum. The 3 stages are bulk, absorption and float and are required to most efficiently charge a battery from a discharged state to a charged state without damage. A 4th more advanced stage is equalisation which not all controllers have. Also look for a controller where you can select the battery type – wet/flooded, Gel or AGM. These common battery types require slightly different voltage settings for optimum charging which are pre-programmed into the controller.

Maximum Power Point Tracking

A MPPT controller uses a completely different technology and algorithm to charge a battery. The downside of PWM controllers is that when used with higher voltage solar panels the ‘additional’ voltage is simply wasted as heat, reducing charging efficiency. MPPT controllers however make use of whatever volts and amps is available from a solar module and converts it to usable charge, thus improving charging efficiency.

To best understand how MPPT controllers work let’s have a look at an I-V curve, which is the performance curve of a solar module. The maximum power point at any given time is the maximum product of volts and amps. The charging algorithm automatically looks for this maximum power point improving energy efficiency by as much as 20% at a given instant compared to PWM controllers.

IV curve