8 | SAMLEX AMERICA INC.
SAMLEX AMERICA INC. | 9
SECTION 4 |
Principles of Operation
4.2 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. Average impedance may be assumed as 20
milli Ohm or 0.02 Ohm.
When the charger is delivering a constant voltage under Absorption/ Float Stages (
is
supplying current < its Bulk Stage Current value
), the charging current drawn by the bat-
tery can be roughly calculated as follows:
Charging current = (Charger Voltage - Intrinsic battery voltage) ÷ Internal resistance (0.02 Ohm)
For example, when SEC-1250UL is in the Bulk Charge Stage 1 (
Fig 4.1
), its output voltage
is set at 13.5 VDC. When a battery discharged to say 10.5V is charged, it will try to draw
very large current = (13.5V - 10.5V) ÷ Internal resistance (0.02 Ω) = 150A. SEC-1250UL
will, however, limit this current to 50A.
4.3 CHARGING STAGES AND CHARGING CURVES
These chargers are designed to provide the following 3-Stage / 2-Stage charging algo-
rithms for Lead Acid Batteries (
Flooded / AGM / Gel Cell types
)
•
3-Stage Charging Algorithm
: Bulk Stage
"
absorption Stage
"
Float Stage for Lead
Acid Batteries
•
2-Stage Charging Algorithm
: Bulk Stage
"
Float Stage. When 2-Stage Charging
Algorithm is selected (
Section 7.4
), the Absorption Stage of the 3-Stage Charging
Algorithm is bypassed. This algorithm is suitable for operation as a Power Supply
(
Section 8.3
) or as a DC UPS (
Uninterruptible Power Supply
) in conjunction with a
battery (
Section 8.4
)
The type of Lead Acid Battery and the desired charging algorithm can be selected with
the help of DIP Switches S1 and S2 (
7 in Fig 3
). For details, please refer to Sections 7.4
Charging Curves for 3-Stage Charging Algorithm are given at Fig 4.1 for SEC-1250UL and
at Fig 4.2 for SEC-2425UL
Details of the 3 stages of charging operation are explained at Sections 4.3.1 to 4.3.3