Samlex America SEC-2425UL - Manuel (Page 7)

6 | SAMLEX AMERICA INC. SAMLEX AMERICA INC. | 7
seCtIOn 4 | Principle of Operation
i
inFo
For complete understanding of working of battery chargers, understanding of
operation of Lead Acid batteries is desirable.
For detailed information on construction, working and application of batteries,
please refer to Application Note titled “Lead Acid Batteries – Construction and
Application” at the following link to Samlex America, Inc. website:
www.samlexamerica.com/support/application_notes.aspx
BAtteRy cHARGeR iS A cURRent liMited dc PoWeR SUPPly
The charger is a current limited DC power supply that converts 120 / 230 VAC, 50 / 60 Hz
to regulated DC voltages and limits the maximum output current as follows:
Model no. current limit
constant
Voltage at Bulk
Stage “i”
constant
Voltage at
Absorption
Stage “U
0
”
constant
Voltage at
Float Stage
“U”
SeC-1250UL 50A 13.5 VDC
14.0 VDC or
14.4 VDC
13.5 VDC
SeC-2425UL 25A 27 VDC
28 .0 VDC or
28.8 VDC
27 VDC
The specified output voltage of the charger during particular charging stage is held
constant till the current limit value is reached. When the battery or DC load tries to draw
current > the current limit value, the charger limits the current to the current limit value
and the output voltage of the charger drops and is no longer constant. When the char-
ger is connected to a battery and is in current limit condition, the terminal voltage of
the charger will be clamped to the actual lower intrinsic terminal voltage of the battery
(assuming the charger is very close to the battery and there is no voltage drop in the
wires connection the charger to the batteries).
BAtteRy iMPedAnce And cHARGinG cURRent
The internal impedance of a healthy battery is very low - in tens of milli Ohms (The
impedance is higher in discharged condition due to Lead Sulfate formation and reduces
when the battery is fully charged – Lead Sulfate gets fully converted to Lead and Lead
Dioxide). Average impedance may be assumed as 20 milli Ohm or 0.02 Ohm
When the charger is delivering a constant voltage (is not in current limit condition), the
charging current drawn by the battery can be roughly calculated as follows:
charging current = (charger Voltage - intrinsic battery voltage) ÷ internal resistance (0.02 ohm)