PWM Charge Controllers
PWM Charge Controllers
Charge controller is an essential part of a solar panel system with a battery. It protects your energy storage and prolongs its lifespan. PWM charge controllers are the simplest type of regulators on the market.
Why do you need a charge controller
Every charge controller should be able to
- protect the battery from high voltage of panels. By connecting a battery to panels without a controller in between, you risk overheating the battery which eventually leads to its early death.
- prevent the overcharging of a battery and its usage in the state of deep discharge, like a smart battery charger.
- block reverse currents: at night energy can flow from a battery back to PV modules. Not only are you losing energy, it can potentially start a fire on a roof.
The charge controller also helps you to monitor your solar panel system. It measures the charge of a battery, shows its current state and tells you the voltage of panels. More advanced models offer additional features, like programming the charging process and measuring the temperature outside.
How a PWM charge controller works
PWM charge controllers are actually really simple. They bring the voltage that comes from panels down to the voltage of a battery. This is why you should always use PWM charge controllers only in situations where the voltage of your panels is slightly higher than the one of a battery — otherwise your panels lose too much power. For example, a PWM charge controller fits a system with 30-cell panels and 12 volt battery. To prevent the overcharging, a PWM regulator limits the energy that it receives and makes a trickle of electric charge for a battery. The PWM controller is a good choice with a small residential solar panel system when you don’t aim to get as much energy as possible.
The simplicity of a PWM charge controllers make them very long lasting — their lifespan oftentimes exceeds 15 years. The warranties for them are usually issued for 2-5 years. Unlike MPPT regulators, they are also very cheap. You can get a PWM controller for $20—$100, so you can easily replace one if it malfunctions for some reason.
The downside of PWM controllers is their low efficiency. They make use only of 70-80% of electric power that flows through them. Besides, they are suitable only for a small range of systems, whereas MPPT controllers are much more flexible. Even in systems where you can use either a PWM or an MPPT controller, an MPPT regulator is 20-25% more efficient.
How to size a PWM charge controller
A PWM controller goes well with
- 30-cell panels and 12V battery
- 60-cell panels and 24V battery
- 120-cell panels and 48V battery
As it is with MPPT controllers, PWM controllers have maximum amps and maximum voltage:
- To figure out the electric current that is going to flow through your future controller, divide the power of your solar array by the voltage of a battery. Amps of your controller should be bigger than that number.
- To calculate the voltage, add together VOCs (open circuit voltage) of every panel in the array. On cold days voltage can go even higher. To take it into account, add 5 volts on top of every panel’s VOC. The maximum voltage of a controller should be bigger than this sum.
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