samlexsolar SCC-30AB, Owner'S Manual, Page: 26 / 48

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INTRODUCTION & FEATURES
PV Systems and associated cabling are installed in exposed locations and hence,
they are more prone to the damaging effects of high voltage transients. Large PV
Systems employ numerous lightning protection devices like Lightning Rods, Surge
Suppressors, shielded cables etc. However, in small PV systems, these protections
are seldom incorporated. Because there is less system level protection, small PV
Charge Controllers are more susceptible to damage by high voltage transients.
Transient Voltage Surge Suppressors (TVSS) are used to protect the input and
output sections of the Charge Controller. The TVSS clamps the high voltage
of the transient to a safe level. The Clamping Voltage is seen by the MOSFET
and temporarily stresses the MOSFET. In a Series Type of Charge Controller,
the MOSFET Switch is located between the input terminals and the battery.
Hence, the voltage seen across the MOSFET Switch during high voltage transient
condition is lower and is equal to the Clamping Voltage of the TVSS minus the
battery voltage. This produces lower stress. On the other hand, in a Shunt Type
Charge Controller, the MOSFET Switch sees the full Clamping Voltage and,
therefore, it is stressed to a higher degree.
• Lesser switching noise. During charging, the Shunt MOSFET Switch experiences
higher level of stress because it is in a high temperature reverse bias standoff
position
• The voltage applied across the Series MOSFET Switch is lesser and hence, it
experiences lesser stress and is, therefore, more reliable
A Shunt Type requires a Schottky Diode in series with the battery to prevent short
circuiting of the battery during the time the MOSFET switch shunts the PV Array. In a
Series Type, this Schottky Diode is not required. Elimination of the Schottky Diode in
the Series Type has the following associated advantages:
• Lower voltage drop, less heating and consequent lower losses
• Reverse leakage through the Schottky is eliminated
Battery Charging Algorithm
Selecting the best method for charging your battery together with a good
maintenance program will ensure a healthy battery and long service life. Although the
SCC-30AB’s battery charging is fully automatic, the following information is important
for getting the best performance from your SCC-30AB Charge Controller and battery.