SECTION 7 |
General Information on Lead Acid
Batteries
19
Reserve capacity is the time in minutes for which the battery can deliver 25 Amperes
at 80ºF (26.7ºC) till the voltage drops to 1.75V / Cell i.e. 10.7V for 12V battery, 21.4V
for 24V battery and 42V for 48V battery.
Approximate relationship between the two units is:
capacity “c” in Ah = Reserve capacity in Rc minutes x 0.6
7.5 TYPICAL BATTERY SIZES
The Table 7.1 below shows details of some popular battery sizes:
TABLE 7.1 POPULAR BATTERY SIZES
BCI* Group
Battery Voltage, V
Battery Capacity, Ah
27 / 31
12
105
4D
12
160
8D
12
225
GC2**
6
220
* Battery Council International; ** Golf Cart
7.6 SPECIFYING CHARGING / DISCHARGING CURRENTS: C-RATE
Electrical energy is stored in a cell / battery in the form of DC power. The value of the
stored energy is related to the amount of the active materials pasted on the battery
plates, the surface area of the plates and the amount of electrolyte covering the
plates. As explained above, the amount of stored electrical energy is also called the
Capacity of the battery and is designated by the symbol “C”.
The time in hours over which the battery is discharged to the “End Point Voltage”
for purposes of specifying Ah capacity depends upon the type of application. Let us
denote this discharge time in hours by “T”. Let us denote the discharge current of
the battery as the “C-rate”. If the battery delivers a very high discharge current, the
battery will be discharged to the “End Point Voltage” in a shorter period of time. on
the other hand, if the battery delivers a lower discharge current, the battery will be
discharged to the “End Point Voltage” after a longer period of time. Mathematically:
EQUATION 1: Discharge current “C-Rate” = Capacity “C” in Ah ÷ Discharge time “T”
