34 | SAMLEX AMERICA INC.
Now, the capacity of the batteries is determined based on the run time and
the usable capacity.
From Table 7.3 “Battery Capacity versus Rate of Discharge”, the usable capacity at
3 Hour discharge rate (C/3) is 60%. Hence, the actual capacity of the 12V batteries to
deliver 300 Ah will be equal to: 300 Ah ÷ 0.6 = 500 Ah, and the actual capacity of the
24V battery to deliver 150 Ah will be equal to 150 Ah ÷ 0.6 = 250 Ah
And finally, the actual desired rated capacity of the batteries is determined based on
the fact that normally only 80% of the capacity will be available with respect to the
rated capacity due to non availability of ideal and optimum operating and charging
conditions. So the final requirements will be equal to:
FOR 12V BATTERY:
500 Ah ÷ 0.8 = 625 Ah (note that the actual energy required by the load was 300 Ah).
FOR 24V BATTERY:
250 Ah ÷ 0.8 = 312.5 Ah (note that the actual energy required was 150 Ah).
It will be seen from the above that the final rated capacity of the batteries is almost
2 times the energy required by the load in Ah. Thus, as a Rule of Thumb, the Ah
capacity of the batteries should be twice the energy required by the load in Ah.
7.17 CHARGING BATTERIES
Batteries can be charged by using good quality AC powered battery charger or from
alternative energy sources like solar panels, wind or hydro systems. Make sure an
appropriate Battery Charge Controller is used. It is recommended that batteries may be
charged at 10% to 20% of their Ah capacity (Ah capacity based on 20 Hr Discharge Rate)
.
Based on the application, batteries may be charged using 2-Stage / 3-Stage / 4-Stage
Charging Profiles as follows:
Float Application Charging (2-Stage)
Stage 1
(Bulk Stage at constant current)
"
Stage 2
(Absorption Stage at constant
voltage. May also be called Float Stage in some applications)
.
Normal Charging (3-Stages)
Stage 1 (Bulk Stage at constant current)
"
Stage 2 (Absorption Stage at constant
voltage)
"
Stage 3 (Float Stage at constant voltage)
Equalization Charging (4-Stages)
Stage 1 (Bulk Stage at constant current)
"
Stage 2 (Absorption Stage at constant
voltage)
"
Stage 3 (Equalization Stage at constant voltage)
"
Stage 4 (Float Stage at
constant voltage)
SECTION 7 |
General Information - Battery Related
