SamplexPower PST-1500-12 Mode D'emploi page 18

SECTION 7 |
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. 10.5V for 12V battery, 21V 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
27 / 31
4D
8D
GC2**
* 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"
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"
0.5 Hrs.
1 Hrs.
5 Hrs. (Inverter application)
18 | SAMLEX AMERICA INC.
General Information on Lead Acid
Batteries
Battery Voltage, V
"C-Rate" Discharge Current in Amps =
Capacity "C" in Ah
12
12
12
6
÷
Discharge Time
"T" in Hrs.
2C
1C
C/5 or 0.2C
Table Continues Next Page }
Battery Capacity, Ah
105
160
225
220
Example of C-Rate
Discharge Currents
for 100 Ah battery
200A
100A
20A