Samlex Power SCC-30AB Manuel Du Propriétaire page 15

SECTION 3 |
• The resistances of the connecting cables will not be balanced.
• The individual batteries will see different series resistances.
• All the individual batteries will be charged at different charging current
and thus, will reach fully charged state at different times.
• The battery with lower series resistance will take shorter time to charge
as compared to the battery which sees higher series resistance and
hence, will experience over charging and its life will be reduced.
Sizing the Battery Bank
The capacity of the battery bank in Ampere Hours (Ah) is determined based on the
amount of energy that is required to be provided for operating the desired DC and AC
loads for desired span of time in hours.
For example, backup energy may be required for say 4 hours or 1 day (24 Hours) or 3
days (72 Hours). In this connection, the following formulae will be applicable:
FORMULA 1
FORMULA 2
DC Power drawn from the
FORMULA 3 Battery by DC load fed directly
DC power drawn from the
FORMULA 4
battery by AC load fed from
Energy consumption from the
FORMULA 5
battery in Watt Hour (Wh)
Energy consumption from the
FORMULA 6
battery in Ampere Hour (Ah)
Determining Total Battery Energy Consumption – First step is to determine the total
battery energy consumption in Ampere Hours for running the desired AC and DC
loads during the desired span of backup time:
a) Find out the power rating of each AC and DC device in Watts (W). If Watt
rating is not available, calculate the Watt rating using Formulae 1 or 2.
b) Determine / calculate the power drawn from the battery in Watts (W) by
each of the AC and DC devices. For DC devices, this will be the same as its DC
Power rating (Formula 3). For AC devices powered from DC to AC inverter,
use Formula 4 to calculate the power drawn in Watts (W) from the battery.
Description & Principle of Operation
DC Power in Watts (W)
AC Power in watts (W)
from the battery
DC-AC inverter
Table 3.6. Battery Sizing Formulas
DC Volts (V) x DC Current (A)
AC Volts (V) x AC current (A) x Power
Factor (0.8 Typical)
Power of DC load in Watts (W)
1.2 x Power of AC load in Watts (W)
(Assuming typical efficiency of
inverter = 84%)
Power in Watts (W) x time in Hours (h)
12v Energy consumption in
Battery Watt-Hour (Wh) ÷ 12
24v Energy consumption in
Battery Watt-Hour (Wh) ÷ 24
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