PWM vs. TrakStar MPPT Technology

Traditional PWM vs Morningstar’s TrakStar™ MPPT Technology
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It is important to note that exceeding the maximum array wattage for a given
controller/nominal voltage combination will not damage the controller.
Array Sizing for MPPT Regulators:
As with PWM regulators, the most basic concern when sizing an MPPT solar array is open circuit
voltage (Voc). The temperature compensated (see Appendix) Voc of the array must be less than the
maximum input voltage rating of the MPPT controller. Higher Voc has the potential to damage the
unit.
For a given MPPT current rating and nominal system voltage, there is an effective maximum
solar array wattage that can be used. Morningstar MPPT controllers have current ratings which specify
the maximum battery charge current the unit can support. NOTE: The battery charge current will be
lower than the solar input current due to the MPPT’s ability to “boost” charging amperage. The MPPT
output current rating multiplied by the battery voltage is the maximum amount of power which can be
used for charging the batteries. Any amount of power in excess of this could be lost when the controller
limits the charging current to the maximum output current level:
Example #1:
o A 15A MPPT controller is being used in a 12V nominal system (actual battery voltage
between 10V and 15V).
o Multiplying current rating and battery voltage gives about 200W (15A * 13.3V = 200W).
o The recommended maximum array wattage for this system is therefore 200W.
Example #2:
• A 15A MPPT controller is now being used in a 24V nominal system (actual battery voltage
between 20V and 30V).
• The recommended maximum array wattage will therefore be 400W (15A * 26.6V = 400W).
It is important to note that exceeding the maximum array wattage for a given controller/nominal
voltage combination will not damage the controller. Any wattage in excess of the max array
wattage will simply be lost. (i.e. Using a 300W array in a system where the max array W is only 200W
will not damage the controller, but the 300W array will have an operating power of approximately
200W maximum).