How Big of a Charge Controller Do I Need?
The answer to this question starts with how much solar do you have and what size and voltage battery do you want to charge? There are two basic types of charge controllers - PWM and MPPT.
The answer to "What size solar charge controller does your system need?" starts with by asking how much solar do you have and what size and voltage battery do you want to charge?
There are two basic types of charge controllers:
- PWM – Pulse Width Modulation Charge Controller - A “switch” turns on and off at set parameters to prevent overcharging your battery. The solar panel needs to be the same voltage as the battery, because you’re connecting the panel directly to the battery with a “switch” between the two. The battery dictates the output of the panel so there’s a considerable loss factor, usually around 30% loss of output. PWM charge controllers are simple and therefore generally less expensive, but they’re not “smart”.
- MPPT – Maximum Power Point Tracking Charge Controller - Some people say that you gain up to 30% output with MPPT, but it is the 30% that you lose with PWM. Simply put, there is a transformer between the battery and the solar panel so the battery can’t bully the solar panel output. All this is controlled by a processor which adds features. In the end, the solar panel can produce all it can at any given time thus utilizing its potential. Most MPPT controllers will allow you to come in at substantially higher voltage thus giving you the option of going further with smaller wire from the panels to the controller.
What Size Controller to Get
Add up the total watts of solar panels and divide by either 14.4 for 12-volt systems 28.8 for 24 volts or 58.8 for 48-volt battery banks. This will give you maximum output amps from the controller. If you don’t want to waste output in heat, size the controller at around two-thirds the rated output of the controller.
- 20 amps is good for a 30-amp controller
- 45 amps is perfect for a 60-amp controller
- 65 amps is about right for an 80-amp controller
Using these guidelines, the system won't run hot or waste precious energy. In addition, the fan won’t fail prematurely, which is important because if that happens, the controller could release smoke that will be very tough to get back in.