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Solar Charge Controllers

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As a battery gains a higher level of charge, the best voltage at which to charge it changes. Charge controllers improve battery life by tracking a battery's state of charge and adjusting charging voltage accordingly.

What is a charge controller?

The charge controller regulates the electric current that is flowing into and out of the battery bank, motor, or pump. By controlling the rate of electric current, charge controllers prevent overcharging and can protect against over-voltage which could damage the battery or motor. A charge controller can also prevent totally draining ("deep discharging") a battery, or perform controlled discharges, depending on the battery technology, to protect battery life.

MPPT or PWM Charge Controller?

Maximum Power Point Tracking charge controllers (MPPT) and Pulse Width Modulation (PWM) charge controllers are two types of charge "regulators" for renewable energy systems. They regulate the flow of electricity from the power generation system into the load or storage system. MPPT charge controllers are the most efficient type on the market but are also more expensive. MPPT and PWM technologies are not mutually exclusive, you do not have to use one or the other.

Several charge controllers use both technologies, but adding MPPT circuitry to a charge control increases the cost. When choosing the right solar charge controller, you'll need to consider how many panels you are using, what your battery bank power storage capacity will be and how much load your power system will create. You should also consider how long you will need to run the system (years). The annual power gains from an MPPT charge controller can offset the cost savings of a controller only using PWM in many situations. But a properly matched PWM can be much more cost effective especially for smaller installations.

MPPT charge controllers have the best performance, but they are more expensive

Why do MPPT charge controllers have the best performance? Because they allow your solar panels to operate at their optimum voltage levels in varying light conditions; summer, winter, morning, noon, cloudy etc... The MPPT charge controller takes the voltage output of the solar panels, and compares it to the battery voltage. It then figures out what is the best voltage to get maximum AMPS into the battery. Remember it's the AMPS that matter. Said another way, the MPPT controller tracks the best voltage level and then down converts it to the voltage of your system (12, 24, 48VDC). This "tracking" of the optimal power point improves performance by as much as 30%. PWM charge controllers on the other hand, reduce the voltage from the solar panel to that of the battery bank resulting in a decrease in efficiency. The efficiency loss depends on the size of the voltage mismatch between your panels and batteries.

A closer look at a Morningstar Tristar Charge Controller.

Another benefit of MPPT charge controllers is that many can accept high input voltages (up to 120+V DC) and efficiently down convert the DC voltage to that of your system (e.g. 12, 24, 48VDC, etc) which means you aren't losing any generated power and you are able to use what you generate more efficiently. Additionally, using a much higher DC voltage on the input side allows you to use thinner wire, decreasing your wire cost and making installation easier.

PWM charge controllers are less expensive and you will find a wider selection of models available. They are ideal for smaller systems where price point is critical or where the additional power is not really needed. Remember, your solar charge controller is an integral part of your system, stick with the brand names from reputable dealers for safe, long term success with your solar electric project!

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