DIY Manual

6 | P a g e 10-543-1 REV A
DIY Manual
appropriate charge controller, which will determine how the panels are wired together, which
will bring us back to how many panels can be wired together, 3 or 4.
Step 4 CHARGE CONTROLLER SIZING
Charge controllers come in two flavors: Pulse Width Modulated (PWM) and Maximum Power
Point Tracking (MPPT).
A PWM controller is simple in concept and inexpensive in cost compared to an MPPT controller.
PWM means the controller varies the width of the output pulse to the battery bank, thus
regulating the charging current through pulse width – wider width means more current. When
the PWM controller senses the bank is filling up, the pulses are reduced in width, thus decreasing
current flow to the batteries. A PWM controller couples the solar panel output voltage to battery
voltage. Therefore, if you have a 12V bank you will want a solar panel with about an 18 Vmp
output, for example.
An MPPT controller tracks the solar panel’s power curve (IV curve) using an algorithm-driven
program to find the highest power point (Vmp) on the curve. The Classic and KID MPPT charge
controllers constantly sweep for optimal Vmp.
MPPT charge controllers require an input voltage that is 133% higher than the highest battery
bank charging voltage (i.e., the Equalization charge voltage). This voltage differential is what
generates up to 40% more current than a PWM controller. In a 12V system, the Classic 150
operates optimally with an input of 70-90V. Refer to the Classic Owner’s Manual to review the
Classic Power Graphs for the Classic 150, Classic 200, and Classic 250 charge controllers for banks
from 12V to 72V.
Now we go back to the unanswered question of how many PV panels are needed for our example,
3 or 4 panels? Knowing the input to an MPPT controller must be higher than Batt V, we consider
how many panels will be wired in series and presented to the MPPT controller.
Our continuing example calls for 3.8 panels …
Max Power Point or Vmp
Max Voc
Max Isc