Determining Battery Size Necessary For Backup Power - Siemens System 3 Manual

Section VI — Power Calculations
4. DETERMINING BATTERY SIZE NECESSARY
FOR BACKUP POWER
a. Select the graph on Charts A, B, or C
that seems most appropriate for the
system configuration. Select the
correct battery curve, depending upon
whether the battery is needed for a
passenger ship (36 hours of battery
operation) or any other type of ship (18
hours).
b. Mark the needed supervisory current on
the Y- axis and draw a straight line
parallel to the X-axis between the point
marked and the appropriate curve of
the battery being considered.
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c. Mark the needed alarm current on the X-axis
and draw a line parallel to the Y-axis between
that point and the appropriate curve of the
battery being considered.
d. If the intersection of these two lines falls
within the battery curve, that battery capacity
is sufficient to handle the system.
e. If the intersection point falls above the curve
or near the center of the curve, repeat the
calculations on the curve of either a larger or
smaller battery, as necessary, until the
necessary battery capacity is found.