20 | SAMLEX AMERICA INC.
SAMLEX AMERICA INC. | 21
Normal Lead Acid Charging Algorithm
Please refer to Fig 4.2A
Stage - 1: Bulk Stage. During night, the battery voltage will drop below the Float
Transition Voltage Set Point “Vf” (Curve portion A to B), as there is no sun and discharging
takes place due to loads that are powered during the night e.g. night lighting.
When the sun is available in the morning, charging commences in Bulk Stage.
During this stage (Curve portion B to C), the Switch is kept at 100% Duty Cycle (ON
continuously) and hence, maximum current equal to the available Short Circuit
Current “Isc” of the panel is fed to the battery and the battery voltage starts rising.
This is equivalent to Constant Current Charging. When the voltage reaches the
Absorption Regulation Voltage Set Point “Va” (Point “C”) and is sustained for a
minimum period of around 50 to 55 sec, the controller transitions to Absorption Stage.
At the end of the Bulk Stage, the battery is charged to around 80% capacity. The
balance of 20% capacity is restored in the next Absorption Stage.
During this stage, the LCD Screen 4 (Fig 5.3) on page 32 shows “State: Bulk”. Screen 1
(Fig 5.3) shows the actual terminal voltage of the battery under “BatV”.
Stage - 2: Absorption Stage. The controller enters this stage at Point “C” from
the previous Bulk Stage when the battery voltage reaches the Absorption Voltage
Regulation Set Point “Va” and is sustained for a minimum period of around 50 to 55 sec.
This stage is timed for 1 Hr - either continuous or cumulative (Curve Portion C to D).
In this stage, the Switch operates under PWM control by feeding pulsing Short Circuit
Current “I
SC
” with constantly reducing Duty Cycle (< 100% and > 0%) / average current
to keep the battery voltage constant at the Absorption Voltage Regulation Set Point
“Va” (Curve portion C to D). This is equivalent to Constant Voltage Charging. This is an
intentional, controlled over voltage condition for the battery for 1 Hr. This is necessary
to return the balance 20% of the capacity. At this voltage, the battery starts gassing
(evolution of Hydrogen and Oxygen due to electrolysis of water in the electrolyte) and
hence, it is necessary to exit this stage as soon as 100% capacity is restored. If this over
voltage condition is allowed to continues after 100% recharging, the battery will be
damaged due to effects of overcharging like overheating, loss of water, corrosion of
the Positive plates and excessive build up of pressure resulting in acid spillage due to
opening of pressure activated relief valves (sealed batteries). The balance of 20% of
the battery capacity is restored in this stage. As the battery capacity rises from 80% to
100%, the PWM control tapers the current by continuously reducing the Duty Cycle
from < 100% to > 0%.
NOTE: Change over to the next Float Voltage Regulation Set Point “Vf” is possible
only after the battery voltage is held at the selected Absorption Voltage
Regulation Set Point “Va” for continuous or cumulative period of 1 Hour. If
“Va” cannot be maintained continuously / cumulatively for 1 Hr, transition to
Float Stage will NOT take place (the periods during which the battery voltage
falls below “Va” are not counted towards 1 hour time period).
SECTION 4 |
Principle of Operation & Features
Summary of Contents for samlexpower SCC-30AB
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