Charge Controllers

Solar charge controller is a regulator that is use in off-grid and grid-tie with battery backup systems to control the flow of voltages and current coming from the solar panels going to the battery. Most solar panels output far more voltage than the required battery voltage, so if there is no regulation the batteries can be damaged from overcharging so the controller is place between the panels and the batteries to limits the rate at which the solar current is added to or drawn from the batteries and so doing prevents overcharging or undercharging which can reduce the batteries performance or lifespan, it also prevent the battery from completely discharging when they are being used. Some charge controllers can show system operation parameters, battery status and protection from over discharging. The capacity of charge controllers ranges from 4 amps to 80 amps. The two most use charge controllers are Pulse Width Modulation (PWM) and Maximum Power Point Tracking (MPPT) technology. PWM controllers are a time-tested traditional technology that has been around for many years they are robust, inexpensive and widely used in solar installation applications but although very efficient they are no comparison with the newer MPPT the shining star of today’s solar systems. MPPT controllers track the maximum point of power (constantly scanning the VI curve) thousands of times per minute, these controllers actually detect the optimum operating voltage and amperage of the solar panel array and match that with the battery bank. The result is additional 15-30% more power out of your solar array versus a PWM solar controller.

Features of some of today€™s intelligent solar Charge Controller include:

  • Maximum Power Point Tracking (MPPT) delivers maximum available power from PV array to battery bank
  • Integrated PV ground-fault protection
  • Ultra-reliable, convection-cooled design does not require a cooling fan ˆ’ large, aluminum, die-cast heat-sink allows full output current up to 45°C without thermal derating
  • Selectable two or three-stage charging algorithms with manual equalization to maximize system performance and improve battery life
  • Configurable auxiliary output
  • Liquid crystal display (LCD)
  • Input over-voltage and under-voltage protection, output over-current protection, and back feed (reverse current) protection (warning and fault messages appear on LCD when unit shuts down as a protective measure)
  • Over-temperature protection and power derating when output power and ambient temperature are high
  • Battery Temperature Sensor (BTS) included – automatically provides temperature compensated battery charging
  • Network communications
  • Communicates settings and activity to other enabled devices, such as the Inverter/Charger, System Control Panel Automatic Generator Start.
  • Five-year warranties

A solar charge controller is similar to the voltage regulator in your car. It regulates the voltage and current coming from the solar panels going to the battery. Most €œ12 volt€ panels outputs about 16 to 20 volts, so if there is no regulation the batteries will be damaged from overcharging. Most batteries need around 14 to 14.5 volts to get fully charged.

Not always, but usually. Generally, there is no need for a Solar Controller with the small maintenance, or trickle charge panels, such as the 1 to 5 watt solar panels. A rough rule is that if the panel puts out about 2 watts or less for each 50 battery amp-hours, then you don€™t need one.

For example, a standard flooded golf car battery is around 210 amp-hours. So to keep up a series pair of them (12 volts) just for maintenance or storage, you would want a panel that is around 4.2 watts. The popular 5 watt panels are close enough, and will not need a controller. If you are maintaining AGM deep cycle batteries then you can use a smaller 2 to 2 watt panel.

Maximum power point tracker (or MPPT) is a high efficiency DC to DC converter which functions as an optimal electrical load for a photovoltaic (PV) cell, most commonly for a solar panel or array, and converts the power to a voltage or current level which is more suitable to whatever load the system is designed to drive.

The most basic Solar Controller simply monitors the battery voltage and opens the circuit, stopping the charging, when the battery voltage rises to a certain level. Older charge controllers used a mechanical relay to open or close the circuit, stopping or starting power going to the batteries.

More modern charge controllers use pulse width modulation (PWM) to slowly lower the amount of power applied to the batteries as the batteries get closer and closer to fully charged. This type of controller allows the batteries to be more fully charged with less stress on the battery, extending battery life. It can also keep batteries in a fully charged state (called €œfloat€) indefinitely. PWM is more complex, but doesn€™t have any mechanical connections to break.

The most recent and best type of Solar Controller is called maximum power point tracking or MPPT. MPPT solar controllers are basically able to convert excess voltage into amperage. This has advantages in a couple of different areas.

Most solar power systems use 12 volt batteries, like you find in cars. (Some use other voltages and the same advantages apply to these systems as well.) Solar panels can deliver far more voltage than is required to charge the batteries. By, in essence, converting the excess voltage into amps, the charge voltage can be kept at an optimal level while the time required to fully charge the batteries is reduced. This allows the solar power system to operate optimally at all times.

Another area that is enhanced by an MPPT charge controller is power loss. Lower voltage in the wires running from the solar panels to the charge controller results in higher energy loss in the wires than higher voltage. With a PWM charge controller used with 12v batteries, the voltage from the solar panel to the charge controller typically has to be 18v. Using an MPPT controller allows much higher voltages in the wires from the panels to the Solar Controller. The MPPT controller then converts the excess voltage into additional amps. By running higher voltage in the wires from the solar panels to the charge controller, power loss in the wires is reduced significantly.

MPPT charge controllers are more expensive that PWM charge controllers, but the advantages are worth the cost. If you can afford it, you should definitely use an MPPT Solar Controller.

The final function of modern Solar Controllers is preventing reverse-current flow. At night, when solar panels aren€™t generating electricity, electricity can actually flow backwards from the batteries through the solar panels, draining the batteries. You€™ve worked hard all day using solar power to charge the batteries, you don€™t want to waste all that power! The charge controller can detect when no energy is coming from the solar panels and open the circuit, disconnecting the solar panels from the batteries and stopping reverse current flow.

When selecting a Solar Charge Controller, it€™s important to also look ahead €“ if you think you€™ll be adding to your system, it pays to invest in a charge controller rated as high as possible which can save you money when you decide to increase your system size.

Charge controllers are rated by voltage and amperage. The charge controller must be rated matching the voltage of the solar panel array and battery bank. (Usually 12, 24 or 48 VDC) the charge controller must also be rated with enough capacity to handle the current (in amps) coming in from the solar panel array. The basic formula for sizing a solar panel charge controller is to take the short circuit current (Isc) of the array and multiply it by 1.56. (Isc rating is normally printed on the back of the solar panel).

When the rated charge controller is now decided upon we can move to the features we need from it. There are many standard solar charge controllers that work well but others have some great features that will make the renewable energy system more intelligent like the battery temperature sensors. Battery capacity depends on temperature, therefore proper battery charging can be significantly enhanced with a temperature sensor other features includes adjustable control voltage set points, low voltage disconnect, overload protection displays and metering. If D.C loads are to be connected you can connect it directly to the solar charge controller€¦if the solar controller is equipped with a low voltage disconnect (LVD), then the solar charge controller can detect when the battery is low and shut off the DC load until the battery is charged.


  • Nominal battery voltage: 12, 24, 36, 48, 60 Vdc
  • Maximum PV array voltage (operating):
  • Maximum PV array open circuit voltage:
  • Array short-circuit current: Maximum and minimum wire size in conduit
  • Total power consumption while operating:
  • Charger regulation method: Three-stage (bulk, absorption, float), Two-stage (bulk, absorption)