SAMLEX AMERICA INC. | 29
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 re-
lated 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 speci-
fying 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”
Table 7.2 below gives some examples of C-Rate specifications and applications:
TABLE 7.2: DISCHARGE CURRENT RATES - “C-RATES”
Hours of discharge time “T” till
the “End Point Voltage”
"C-Rate" Discharge Current in Amps
= Capacity "C" in Ah ÷ Discharge
Time "T" in Hrs.
Example of C-Rate Discharge
Currents for 100 Ah battery
0.5 Hrs.
2C
200A
1 Hrs.
1C
100A
5 Hrs. (Inverter application)
C/5 or 0.2C
20A
8 Hrs. (UPS application)
C/8 or 0.125C
12.5A
10 Hrs. (Telecom application)
C/10 or 0.1C
10A
20 Hrs. (Automotive application)
C/20 or 0.05C
5A
100 Hrs.
C/100 or 0.01C
1A
NOTE: When a battery is discharged over a shorter time, its specified “C-Rate” discharge current will be higher. For
example, the “C-Rate” discharge current at 5 Hour discharge period i.e. C/5 Amps will be 4 times higher than
the “C-Rate” discharge current at 20 Hour discharge period i.e. C/20 Amps.
SECTION 7 |
General Information on Lead Acid Batteries