Solar charge controllers
How does a solar panel charge controller work?
A solar charge controller harnesses the energy from your solar panels and converts it into usable energy to charge your batteries. The voltage of the solar panels can fluctuate massively depending on the intensity of the sun. Therefore, a solar charge controller is required to regulate the voltage from the solar panels and effectively charge your batteries whilst preventing overcharging. There are two types of solar charge controller available: MPPT and PWM.
MPPT vs PWM
PWM solar charge controllers
PWM solar charge controllers act like a switch between a solar panel and a leisure battery, drawing power from the solar panels at just above the battery voltage. They are a low cost option, and are usually used in more basic systems where the solar panels are being used to trickle charge the leisure battery. An example of this is when solar panels are being used as a backup charging source to shore power.
MPPT solar charge controllers
MPPT solar charge controllers are more sophisticated than their PWM counterparts, drawing power from the solar panels at the ‘maximum power voltage’ (the voltage when the power output is greatest). MPPT charge controllers are therefore more efficient than PWM charge controllers, which means they charge your batteries faster. This is why MPPT solar charge controllers are more commonly used.
How to select a solar charge controller
MPPT charge controllers need to be sized correctly according to the total wattage of your solar panels. Victron solar charge controllers have two numbers to help you decide on the correct charge controller for your system. The first number refers to the ‘maximum PV open circuit voltage’. The second number refers to the maximum charging current. Use our calculator below to help you select the right solar panel charge controller for your system. If you’re not sure how many solar panels you need, you can use our solar panel calculator (coming soon!).
Solar charge controller calculator
Our solar charge controller calculator is based on a 100W solar panel having a max PV voltage of 21.6V and a max charging current of 5.7A. A 25% factor of safety is added to the total max charging current.
When panels are connected in series, the voltages are summed and the current remains the same. When panels are connected in parallel, the amps are summed and the voltage remains the same.
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Need help with the rest of your electrical system?
If you’re looking for an overview of campervan electrical systems, have a read of our campervan electrical system guidebook page. Alternatively, if you need to size the rest of your electrical system, try out one of our other calculators.
