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Schneider Electric manufactures two types of Solar Charge Controllers, the C-series and the MPPT-series. This document will provide a basic understanding of how each unit works and what are the key differences between the two series.
First lets talk about the C-series:
This units come on three difference sizes, C35, C40, and C60. Each one of them is rated for 35A, 40A, and 60A of charging respectively. The C-series works using PWM, which stands for Pulse Width Modulation. PWM works as a series of pulses which provide ON/OFF switching to a voltage source based on a time frame, the average between the pulses width provides the voltage needed. The following is an image that provides and example of the information described above.
Now lets cover the MPPT-series:
This units come on two different sizes, MPPT60-150 and the MPPT80-600. Each one of this units can provide 60A of charging and 80A of charging respectively. The MPPT units use an algorithm called Maximum Power Point Tracking. MPPT algorithm considers several aspects of the power being provided by the PV Panels in order to harvest as much power as it can possibly get. The two main aspects it monitors is the Voltage (V) versus Current (I) curve. This units will lock their capability of harvest on what is called the knee curve. The knee curve is a basic Voltage versus Current curve that provide the efficiency of the PV panels. The best efficiency point of this curve is right where the voltage and the current curve hit the same point, which look like a knee, hence the name of the curve. The following graph shows a normal V vs. I curve.
Notice that the MPPT harvest point is the BLUE line that is plotted accross each curve.
Now lets talk about the differences between PWM and MPPT :
PWM is a less efficient unit than the MPPT, because the C-series acts like a switch that connects the array to the battery, i.e. the battery voltage will determine the operating voltage of the modules. For this reason, the C-series requires the array to be configured to the same nominal voltage as the battery bank that is going to be charge with it. The MPPT series can track the maximum power voltage throughout the entire range of input PV voltage (at least 5VDC higher than the target BULK voltage up to the maximum MPPT voltage). The MPPT cannot "boost" from a lower PV voltage to a higher charge voltage, however.