PWM vs. TrakStar MPPT Technology

Traditional PWM vs Morningstar’s TrakStar™ MPPT Technology
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Recommended values for Vmp are listed below:
12V systems: Vmp > 15V
24V systems: Vmp > 30V
36V systems: Vmp > 45V
48V systems: Vmp > 60V
A PV module’s output current will decrease significantly at voltages higher than Vmp and will be 0
Amps at Voc. Therefore, the temperature compensated Vmp of the array should be higher than full
battery voltage to ensure effective charging over the entire battery voltage range.
NOTE: The Vmp of the array should be higher than, but as close to, the maximum battery voltage as possible. Vmp
significantly higher than max battery voltage reduces efficiency and puts more stress on the switching components of the
regulator. Typically, for proper performance, 36 Cell or 72 Cell off‐grid modules (Vmp ≈ 17 to 18 V for every 12V nominal
battery voltage) should be used with PWM controllers.
Finally, the current output of the array is considered. Unlike MPPT controllers, standard PWM
controllers are not able to “boost” the amount of charging current by converting excess input voltage
into amperage. This means that the input current from the solar array will be equal to the output
current delivered to the battery. The solar array must be sized so that the short circuit current (Isc) does
not exceed the nameplate current rating of the controller being used. An array with Isc greater than the
current rating of the regulator may consistently trip overcurrent protections or damage the unit.
IMPORTANT: Local code may require additional reductions in maximum input Isc levels.
NOTE: Morningstar offers a String Sizer tool to assist in the proper sizing/configuration of your solar array with
Morningstar controllers. Users may choose between a selection of pre‐populated module data or input their own module
specifications. This tool also allows adjustment of design parameters such as range of expected battery voltages and min/max
temperatures at the site. A link to the String Calculator can be found on the Morningstar homepage:
www.morningstarcorp.com
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