May `77
ALTERNATOR CHARGING AND DEAD BATTERY RELATIONSHIP
1. Reports from the users have indicated that some CCE-IHC 20 Ton Dump Trucks are experiencing a problem in
keeping the batteries in sufficient state of charge to start the engine in the morning. The CCE Dump Truck is equipped
with a Cummins NTC 290 Diesel, a high torque 12-volt starter motor, an 80 amp capacity SAE J180 alternator, and 4
each, 6-volt batteries in series-parallel arrangement. These component ratings are commercially matched to start this
engine and maintain charged batteries in heavy duty commercial dump truck service.
2. The Cummins Diesel with 855 cubic inch displacement demands a large quantity of electrical power from the batteries
to start. The colder the weather, the more power that is required. The starter current draws nearly 900 amperes from the
two 12-volt pairs of 6-volt batteries. After engine start, the state of charge of the batteries tells the alternator how much of
its 80 amp capacity the alternator needs to produce to replace the quantity (amps) of electricity used in starting. The
many factors involved in recharging the batteries include interrelationship of alternator output, engine speed, time of
recharge, and condition of wiring at each connector including frame grounds. Table 1 illustrates the dead battery
problems.
3. For normal service involving sufficient truck operational time, the alternator is sized and the batteries have the
capacity to maintain the truck operational. For abnormal service where the truck is only exercised occasionally, the
batteries should be connected to a portable battery charger as needed to maintain a fully charged condition.
a. Alternators: Higher capacity alternators can be substituted. Any alternator meeting SAE J180, double lug, single
wire, will be interchangeable with the present 80 amp alternator; select from 90 and 103 amp ratings, however, running
time of recharging will still be a major factor in keeping the batteries charged. Substituting a 103 amp alternator for the
present 80 amp alternator will result in only a slight decrease in time needed for recharging the batteries. The present
engine to alternator pulley speed ratio is 2.8:1. This provides a 5900 maximum alternator RPM at 2100 engine governed
RPM. For long life and maintenance-free alternator operation, do not repulley this or any alternator to exceed the
maximum of 6000 alternator RPM at engine governed RPM.
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