User Manual

– 5 –
Figure 2 below may be used to determine the minimum
battery size, expressed in Ampere hours of capacity. To
determine the required minimum battery capacity, plot
the required discharge current, on the horizontal
axis, against time. The point where the current and time
lines intersect on or below the diagonal Ah curve shows
the minimum capacity required for the application. In
practice, if the intersection point of the time & current
does not fall exactly on a particular Ah curve, the next
higher value Ah curve should be used to determine the
minimum battery capacity/size. In addition, it is
recommended that figure 32 (Cyclic Service Life) and
Figure 33 (Float Service Life) and if appropriate, the
constant power calculations in table 5, on page 7, should
be consulted prior to final selection.
Discharge Characteristics
The curves shown in Figure 3 and the discharge
current rates shown in Table 4 illustrate the
typical discharge characteristics of Yuasa NP batteries
at an ambient temperature of 25°. The symbol “C”
expresses the nominal capacity of the battery measured
at a 20-Hour discharge rate. Please refer to General
Specifications on page 3 to determine the nominal
capacity rating of specific NP models. The standard
industry practice to determine the nominal capacity of a
valve regulated lead acid battery is to discharge the battery
under test at its 20-Hour rate to a final voltage of 1.75
volts per cell.
Table 4 shows the different currents that can be drawn
at various discharge capacity rates.
Table 6 shows that the rated nominal capacity of a
battery is reduced when it is discharged at a value of
current that exceeds its 20-Hour discharge rate. This
should be taken into consideration when a battery is
being selected for a particular application.
BATTERY CAPACITY SELECTION
DISCHARGE
FIG 2