Samlex Solar SCC-30AB Mode D'emploi page 30

4
IntroductIon & features
the device is not adequately protected. PV Systems and associated cabling are installed in
exposed locations and 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.
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 so 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.
Four Stages of Solar Charging
Fig. 4.1 represents the 4 stages of charging used in the SCC-30AB
30
2
PWM
ABSORPTION
1
BUL K
CHARGING
NIGHT
Fig. 4.1. Solar Charging Stages
3
EQUAL IZE
4
FL OAT
NIGHT
TIME