samlexsolar SCC-30AB, Owner'S Manual, Page: 16 / 48

16
3
GENERAL INFORMATION: BATTERIES
temperature and discharge rate for a high capacity Lead Acid cell. Note that the cell
voltage diminishes in direct proportion to the remaining capacity.
Fig 3.1 SOC versus Open Circuit voltage
The Lead-Acid Batteries
A basic equivalent circuit of the Lead-Acid battery is modeled by a voltage source
with an equilibrium voltage (V
E
) in series with an internal resistor (R
in
) (see Fig 3.2). It
must be noted here that this configuration can describe only a current state because
the magnitude of V
E
and R
in
are not actually constant, but is function of many
parameters such as state of charge (SOC), temperature, current density, and aging of
the battery.
V
B
V
in
I
B
R
in
V
E
R
load
V
B
V
B
V
in
I
B
I
B
R
in
R
in
V
E
V
E
R
load
R
load
Fig 3.2. Basic equivalent circuit of the Lead-Acid battery for a current state