SECTION 7 |
General Information on Lead Acid
Batteries
29
From table 7.3 “Battery Capacity versus Rate of Discharge”, the usable capacity at 3
hour discharge rate 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 13% of their Ah capacity (Ah capacity based on C-Rate of
20 hr Discharge Time). Also, for complete charging (return of 100% capacity) of
Sealed Lead Acid battery, it is recommended that a 3 Stage Charger may be used
(Constant Current Bulk Charging Stage
Constant Voltage Boost / Absorption
Charging
Constant Voltage float Charging).
In case, Wet Cell / Flooded Batteries are being used, a 4-stage charger is
recommended (Constant Current Bulk Charging Stage
Constant Voltage Boost /
Absorption Stage
Constant Voltage Equalization Stage
Constant Voltage Float
Stage).
WARNING!
1. Before commencing installation, please read the safety instructions
explained in the Section 1 titled “Safety Instructions”.
2. It is recommended that the installation should be undertaken by a
qualified, licensed / certified electrician.
3. Various recommendations made in this manual on installation will be
superseded by the National / Local Electrical Codes related to the location
of the unit and the specific application.
