60A 12V 24V 36V 48V MPPT Solar Charge Controller

In short, the solar charge controller you choose must be able to support the power requirements of your loads, your battery voltage (e.g. 12, 24, 36, or 48V), and your PV current and voltage inputs. Additionally, you will need to consider whether you need a controller with low voltage disconnect, lighting control, or other features or certifications. Your climate, choice of modules, and price will also determine whether you choose a PWM or an MPPT controller.  A good solar distributor will be able to help you size and configure your modules, batteries, and controllers for an optimum system.

The first solar charge controller schematic below (Figure 1) illustrates how a solar charge controller is connected to power a direct current (DC) load, and the second one (Figure 2) pertains to an alternating current (AC) load.

Figure1: Off-grid Diagram with DC Load

When installing a solar charge controller, it is recommended that you connect and disconnect in the following order:

1. Battery to the controller first
2. PV array to the controller
3. Electrical load to the controller

When disconnecting, you reverse that order. The battery provides power to the controller so always make sure that solar and loads are disconnected before connecting or disconnecting the battery from the controller. Connections between the battery, load, PV array, and the controller should have disconnect switches to enhance safety and facilitate ease of installation and breakdown.

In the wire diagram schematic above with DC load, sunlight contacts the solar modules, which convert solar into DC electrical power that it delivers to a charge controller. The charge controller regulates the amperage and voltage that is delivered to the loads and any excess power is delivered to the battery system so the batteries maintain their state of charge without getting overcharged. During the evening when there is no sunlight, battery power is used to run the load.

You’ll notice that the battery is grounded at the negative battery terminal. This is because all our PWM and MPPT controllers have a common negative ground. Therefore, it is possible to establish a common negative ground for the entire system: the solar array, controller, battery, and load. This meets NEC code requirements for grounding. If you need an equipment ground for any metal parts on a controller enclosure, some of our controllers include an equipment ground terminal lug. Otherwise, for our controllers that don’t have this terminal lug, you can connect an equipment ground directly to the controller enclosure.

The next diagram (Figure 2) depicts the components and connections to power an AC load. This diagram with an AC load looks similar to the previous example with a DC load, except that in this example, we have added an inverter to the system. The purpose of the inverter is to convert the DC power from the battery to AC power that can be used to run an AC load like the TV you see in the schematic.

Figure 2: Off-grid Diagram with AC Load

It’s important to note that the inverter is connected and powered from the battery, not the controller’s load terminals like we did in the DC load example. That’s because the inverter can have a high energy surge upon startup, and this high current surge might be higher than the rated capacity of the charge controller, whereas the batteries will be able to meet the high energy surge requirement.

Bulk Charging Voltage

For lead-acid batteries, the initial bulk charging stage delivers the maximum allowable current into the solar battery to bring it up to a state of charge of approximately 80 to 90%. During bulk charging for solar, the battery’s voltage increases to about 14.5 volts for a nominal 12-volt battery.

Absorption Charging

When Bulk Charging is complete and the battery is about 80% to 90% charged, absorption charging is applied. During Absorption Charging, constant-voltage regulation is applied but the current is reduced as the solar batteries approach a full state of charge. This prevents heating and excessive battery gassing. At the end of Absorption Charging, the battery is typically at a 98% state of charge or greater.

Float Charging

Float charging, sometimes referred to as “trickle” charging occurs after Absorption Charging when the battery has about 98% state of charge. Then, the charging current is reduced further so the battery voltage drops down to the Float voltage.

The Float charge of a battery keeps the battery at maximum capacity throughout the day.

Equalization Charging

For flooded open vent batteries, an Equalization charge is applied once every 2 to 4 weeks to maintain consistent specific gravities among individual battery cells. The more deeply a battery is discharged on a daily basis, the more often equalization charging is required. Solar Charge Controller Equalization is for flooded, not for sealed, GEL, or valve-regulated batteries which can be damaged by equalization.

The maximum voltage, listed in the operator manual, that a controller can support. To determine whether your system will operate under this Voc limit you must know the lowest temperature your system will be exposed to, and calculate the voltage produced by your array at that temperature. Exceeding Voc limits will damage your controller.

A solar charge controller is a solar-powered voltage and current regulator. They are used in off-grid and hybrid off-grid applications to regulate power input from PV arrays to deliver optimal power output to run electrical loads and charge batteries. Solar charge converters are also commonly called solar charge regulators.

What Does a Solar Charge Controller Do?

Solar charge controllers maintain batteries at their highest state of charge without overcharging them to avoid gassing and battery damage. Learn more by watching our on-demand webinar below, and by reading the additional information on this page.