Samlexpower SCC-1208L Manuel Du Propriétaire page 9

SECTION 3 |
3.2 SERIES AND SHUNT TYPES OF CHARGE CONTROLLERS
When the MOSFET Switch is connected in series with the Solar Panel and the battery,
the Controller is called Series Type (this controller is Series Type). When it is connected
in parallel across the Solar Panel and the Battery, it is called Shunt Type. In Series Type,
the MOSFET Switch is kept open when the battery is fully charged. The Solar Panel
stops supplying current during this period. In the Shunt Type, when the battery is fully
charged, the MOSFET Switch is kept closed to shunt (divert) the full Short Circuit Current
of the Solar Panel away from the battery.
3.3 ADVANTAGES OF SERIES TYPE OF CHARGE CONTROLLER
A Series Type of Charge Controller has the following advantages over a Shunt Type:
• Power systems experience temporary over voltage conditions. For example, when
lightning strikes, extremely high electrostatic energy is discharged. This energy in-
duces damaging high voltage transients in exposed and unprotected electrical circuit
elements like cables etc. and these high voltage transients are fed to the electrical
devices and cause damage if the device is not adequately protected. Solar Systems
and associated cabling are installed in exposed locations and hence, they are more
prone to the damaging effects of high voltage transients. Large Solar Systems em-
ploy numerous lightning protection devices like Lightning Rods, Surge Suppressors,
shielded cables etc. However, in small Solar Systems, these protections are seldom
incorporated. Because there is less system level protection, small Solar Charge Con-
trollers 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 Volt-
age 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.
• Less switching noise
• During charging, the Shunt MOSFET Switch experiences higher level of stress be-
cause it is in a high temperature, reverse bias stand-off condition
• The voltage applied across the Series MOSFET Switch is lesser and hence, it experi-
ences 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
PWM Charging Control
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