UFC 3 -520-01
June 10, 2002
Starting current of starter motor.
Engine model and make.
Cubic inches displacement. Some battery manufacturers have sizing guidelines
based on the cubic inches displacement.
Number of cranks and possible duration of each crank.
Rest period for battery recovery, if needed.
Worst case low battery temperature.
Worst case low engine temperature and oil viscosity.
Battery type and desired life.
Seismic or vibration requirements.
E-3.5
As part of the sizing process for a diesel engine battery, consider voltage drop
between the battery and the starter motor. The starter motor usually draws significant
current from the battery. For this reason, batteries are often located very near the
diesel engine to minimize the voltage drop caused by the high current. Typical
connecting devices between the battery and the starter motor include:
Cable--resistance varies with cable size and length.
Contactors (relays, solenoid, switches)--resistance less than 0.002 ohms is typical.
Connections--each connection resistance less than 0.001 ohms is typical.
E-3.6
The diesel engine manufacturer usually specifies the minimum system
requirements, including the maximum connection resistance between the battery and
the starter motor. Ensure these minimum requirements are met by the installation.
E-4
CHARGER SIZING.
E-4.1
Size each battery charger to be large enough to power the normal system
loads while recharging a discharged battery within a reasonable amount of time.
Manufacturers recommend a recharge time of 8 to 12 hours. Shorter recharge times
require larger battery chargers and might result in excessive current flow into the battery
during the recharge process. For this reason, 8 hours is usually the minimum recharge
time for a discharged battery. On the high end, 12 hours is often recommended for an
upper limit; however, this recharge time is somewhat arbitrary and 14 hours or 16 hours
might be acceptable, depending on the application and how the recharge is controlled.
The primary consideration is that the charger should be sized to recharge the battery
within a reasonable amount of time.
E-8
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