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General Information 2-21MN2408
Battery Charger
An engine mounted alternator to charge the batteries during operation is an available option.
Standby gensets require a solid state battery charger that is connected to utility power so the
battery is charged continuously while the genset is not running. The battery charger should be
connected to the emergency circuit. The batteries on prime power gensets are charged by the
engine mounted alternator, if equipped.
Harmonic wave forms from solid state battery charges and belt driven alternators can cause the
electronic governor on the engine to act erratically. To avoid this, the output of the battery charger
or the belt driven alternator must be connected directly to the battery or to the battery terminals
on the starter. Make control connections to the genset control using a conduit with a flexible
section at the genset to avoid damage due to genset vibrations.
Battery Cables
The wire size (wire gauge) of the cables connecting the starter to the batteries must be large
enough to ensure the resistance of the cranking circuit is less than the “Maximum Allowable
Resistance of the Cranking Circuit” as shown on the Engine–Generator Set Data Sheet. The total
cranking circuit resistance includes the resistance of the cables from the starting motor to the
battery and the resistance of all relays, solenoids, switches, and connections. The resistance of
various sizes of cables is shown in Figure 2-19. For purposes of calculating cranking circuit
resistance to select cable size, the resistance of each connection can be taken as .00001 ohms
and the resistance of each relay, solenoid, and switch can be taken as .0002 ohms. Figure 2-19
illustrates an example of a typical cranking circuit resistance calculation.
Figure 2-19 Typical Battery Cable Calculations