Types of Solar Charge Controllers

If you’ve poured thousands investing in your solar system, be it a residential setup running multiple rooftop panels, or something that you’ve concocted over time while exploring Australia’s great outdoors, you’ll need a dedicated charge controller to handle the charge from the panels to the batteries. With panels now capable of delivering abundant power from the unrelenting Aussie sun, protecting expensive batteries from too much voltage should be a priority. It’s what feeds all the power-hungry devices you have, not to mention the reliance on stable power delivery if your home is off-grid. Damage to batteries is costly in itself, but this can lead to other unwanted expenses that you’re better off without. Solar charge controllers ensure that your battery gets just the right amount of charge, to keep everything connected running just as it should.  

What is a Solar Charge Controller? 

Charge controllers are electronic devices that you install between the panels and the battery. They regulate the amount of power that reaches the batteries from the panels. Charge controllers are necessary protective devices that adjust the amount of charge the battery gets depending on the optimal charge rate in each battery type. This helps batteries from overcharging, which could lead them to explode. Controllers constantly measure how full or empty the battery is and supply it with the right amount of power at the right time.  

But this is not the sole purpose of a charge controller. It also senses if devices are draining too much power when the charge is extremely low, and cuts them off. When the battery again reaches the desired charge rate it turns the devices on once more. A controller is also good in preventing reverse discharging, especially at night, with power drained from the battery and directed to the panels.  

Types of Charge Controllers 

There are three types of solar charge controllers: a shunt controller, Pulse Width Modulation or PWM controller and a Maximum PowerPoint Tracker or an MPPT charge controller. A shunt controller is a basic on/off control. When the battery voltage is low, the shunt turns on and allows it to be charged from the solar panels until it has been fully recharged, and then turns off. Shunt controllers are rarely used, at least on their own, and a solar battery and multiple battery setups are better protected and provide more efficiency by using either a PWM or MPPT charge controller.  

PWM Charge Controllers 

PWM controllers were the industry standard not too long ago. A PWM controller is a voltage regulator that reduces the voltage required for the battery. It doesn’t change the output current until the battery is nearly full. When the battery nears full charge, the controller turns to pulse width modulation, or the constant topping up of the battery by rapidly turning on and off. This is a good feature because once charging stops, batteries tend to slowly discharge. The downside is that the battery or battery bank needs to be in the same voltage as the panel or panel array. A 12V battery needs to be connected to a 12V PWM controller. To maintain voltage, panels need to be connected in parallel.  

PWM controllers are suited for smaller solar setups with few panels, running only basic devices, like lights and a fridge. The advantage is the price, with a decent PWM controller an inexpensive buy. For larger systems though, you need to step up to an MPPT charge controller 

MPPT Charge Controllers 

PWM controllers have been largely replaced by MPPT solar charge controllers. They can be used to pair batteries and panels in different voltages. An MPPT acts as a power regulator or DC converter, meaning they can accept any input of power and convert it into the appropriate battery voltage. And this often is the maximum power voltage. There is less voltage drop in the wiring between panels and battery banks, and hence more efficiency. This means panels can be hooked up in series, allowing for thinner cables routed at longer distances. Though you might save some cash in cables, MPPT controllers are considerably more expensive, but the option for most solar setups with multiple batteries fed from several panels is to run a larger number of devices and appliances.  

But you get what you pay for. An MPPT controller is estimated to be up to 25 per cent more efficient than a PWM controller. Also, it can use the maximum voltage of the solar array to charge batteries much quicker. This is the controller to have in a residential off-grid solar setup, or one in a caravan or motorhome. These systems will already have much put toward it, and an efficient and effective MPPT controller will safeguard that investment.  

PWM or MPPT? Which Suits You? 

If you’re the occasional camper, running a few devices off a 12V panel (or two) through a cheap lead-acid battery, then definitely get a PWM controller. If you have a complex off-grid residential or camping setup, consisting of several panels, and intend to upgrade that system in the future by adding more devices and appliances, then a fully-featured MPPT charge controller is what to get. Not only is it more efficient, but is less hindered in changes in weather, and allows more flexibility in where you place each component. A bit costly, yes, but in line with what you already have.