MAINTENANCE OF DC ELECTRICAL AND CONTROL SYSTEM
SECTION I. WIRING HARNESS OVERHAUL
4-1. GENERAL. Electrical interconnection of control devices and indicators is accomplished through wiring harnesses.
Wires in the harness are bundled and secured to prevent unnecessary movement and chafing.
4-2. WIRING HARNESS OVERHAUL. If 30 percent of the wires in a harness are defective, the harness must be
overhauled. FO-1 3 through FO-38 are wiring harness fabrication drawings. These drawings specify the length and gage
of every wire used in each harness, as well as the termination points, lugs, or connectors, and wire marking data. The
harness drawings also provide routing information for each harness. The following is a list of the dc wiring harnesses
with a functional description of each.
The harness that are combination ac and dc are listed in Chapter 5.
Cabinet A Interconnect Harness (80-7897). Refer to FO-1 3. Interconnects all meters, relays, and other
electrical components located in cabinet A.
Fuel Monitor Harness (80-7920). Refer to FO-1 4. Interconnects the floats in the fuel tank with fuel level gage
M4, fuel transfer pump, and annunciator alarm system.
SECTION II. BATTERY CHARGER BC1 REPAIR
4-3. GENERAL. Refer to Figure 4-1. The battery charger BC1 is designed to maintain the generator set batteries BT1
through BT4 in a fully charged condition at all times. The battery charger BC1 receives 120 V ac current from the
generator set ac electrical system and is protected by BATTERY CHARGER circuit breaker DP2CB116. An ac input fuse
ACF protects the internal circuitry of the primary system. A power transformer PT steps down the 120 V ac current to 24
V ac and a set of diodes SD1 converts this ac current to dc. This 24 V dc current is then applied directly to the generator
set batteries BT1 through BT4. A dc output fuse DCF, located after the diodes SD1, protects the system. An ammeter
A, located just ahead of the generator set batteries BT1 through BT4, measures the output rate of the battery charger
BC1. A dc voltmeter V, installed across the positive and negative output from the leads battery charger BC1, measures
the voltage of the generator set batteries BT1 through BT4. The equalizer timer ET, placed between the current sensing
circuitry of the battery charger BC1 and the resistor RV1, is used to manually select the rate of charge (float or equalizer)
and the charging duration. The current sensing circuitry of the battery charger BC1 continually senses battery and load
conditions and provides the appropriate output rate.
As the generator set batteries BT1 through BT4 approach an optimum preselected voltage, the battery charger BC1
equalizer output rate tapers to the float output rate, which maintains the generator set batteries BT1 through BT4 in a
fully charged condition. If the equalizer timer ET has been manually set to the equalizer rate, it will automatically select
the float rate once it times out, and control of the charging rate is returned to the current sensing circuitry. The saturable
reactor assembly SR operates with the current sensing circuitry of the battery charger BC1 to determine the rate of
charge, and helps to compensate for line voltage variations of +l 0 percent.
4-4. REMOVAL OF BATTERY CHARGER BC1. Remove battery charger BC1 in accordance with paragraph 4-20 of
the Operator and Organizational Maintenance Manual.