TTERIES
REDUCTION IN USABLE CAPACITY AT HIGHER DISCHARGE RATES.
As stated above, the rated capacity of the battery in AH is applicable at a discharge rate of
20 Hours. As the discharge rate is increased, the usable capacity reduces due to “Peukert
Effect”. This relationship is not linear but is more or less according to the table below:
Table 1 Battery Capacity versus Rate of Discharge
Hours of Discharge Usable Capacity
20 100%
10 87%
8 83%
6 75%
5 70%
3 60%
2 50%
1 40%
Using the above table will show that a 100 AH capacity battery will deliver 100% (i.e.
full 100 AH) capacity if it is slowly discharged over 20 hours at the rate of 5 Amperes.
However, if it is discharged at a rate of 50 Amperes then theoretically, it should provide
100 AH ÷ 50 = 2 hours. However, the Table above shows that for 2 hours discharge rate,
the capacity is reduced to 50% i.e. 50 AH. Therefore, at 50 Ampere discharge rate the
battery will actually last for 50 AH÷50 Amperes = 1 Hour
UNITS OF BATTERY CAPACITY
The battery capacity is the measure of the energy the battery can store and deliver to a
load. It is determined by how much current any given battery can deliver over a stipu-
lated period of time. The energy rating is expressed in Ampere Hours (AH). As a bench
mark, the battery industry rates batteries at 20 hour rate i.e. how many Amperes of
current the battery can deliver for 20 hours at 80 º F till the voltage drops to 10.5 Volts
for 12 V battery and 21 V for 24 V battery. For example, a 100 AH battery will deliver 5
Amperes for 20 hours. Battery capacity is also expressed as Reserve Capacity (RC) in
minutes. Reserve capacity is the time in minutes for which the battery can deliver 25
Amperes at 80 º F till the voltage drops to 10.5 Volts for 12 V battery and 21 V for 24 V
battery. Approximate relationship between the two units is as follows:
Capacity in AH = Reserve Capacity in RC minutes x 0.6
TYPICAL BATTERY SIZES
Below is a chart of some battery sizes applicable for powering
inverters:
BCI * Group Battery Voltage, V Battery AH
27 / 31 12 105
4 D 12 160
8D 12 225
GC2** 6 220
* Battery Council International ** Golf Cart
Page 6
To Next Page
Loading...