DIY Manual

46 | P a g e 10-543-1 REV A
DIY Manual
CLASSIC CHARGE CONTROLLER
This chapter of the DIY Manual explains important characteristics of the Classic charge controller
and presents insight and troubleshooting tips gleaned from thousands of Tech Support calls.
Please read in junction with the Classic Owner’s Manual for a complete understanding.
CLASSIC EXPLAINED
Maximum Power Point Tracking (MPPT)
MPPT checks the output of the photovoltaic (PV) modules, compares that output to battery
voltage, then fixes what is the best power the PV modules can produce and converts the PV
output to the best voltage to get maximum current into the batteries. Maximum power varies
with solar radiation, ambient temperature, and solar cell temperature, and is most effective
during cold weather and cloudy days.
MPPT tracks and controls the Maximum Power Voltage, or Vmp, of the PV module(s). Whereas
the Open Circuit Voltage, Voc, is an important design consideration when determining how many
PV modules to wire in a series string as PV input to an MPPT charge controller, Vmp is the voltage
used to make power. Vmp is the voltage component, and Imp is the current component, of the
IV Power Curve. When you read about an MPPT charge controller “sweeping” the power curve,
this means the controller is looking at the point on the power curve in which Vmp is maximum.
Voc and Vmp
On the back of a PV module is a factory sticker with performance specifications, to include Voc,
Isc, Vmp, and Imp.
Voc – Open Circuit Voltage: If the PV module is exposed to the sun, with both the positive and
negative module wires disconnected, Voc is the voltage you will measure with a multimeter. Voc
exists with daylight; Voc is a function of light illuminating the PV module. When Voc is maximum,
current flow is zero, due to an infinite resistance in the circuit. This is shown by the power
formula: P = V x I.
P = V x I