D3-6 24VDC Electrical System Components D03026
BATTERY EQUALIZER BOX
Most truck control and accessory circuits operate at
24VDC. However, a 12VDC Power Source is avail-
able for the cigar lighter socket, power window
motors, and AM/FM, communications and dispatch
radios.
For this purpose, a battery equalizer system is uti-
lized to obtain the required 12VDC and insure that
the two pairs of 12 volt, series wired batteries are
charged and discharged equally.
The battery equalizer is mounted in a box on the right
hand deck. This box also contains the DDEC circuit
breakers (when equipped with DDC 4000 engine),
12VDC control relay, 12VDC circuit breaker, and the
main battery disconnect switch. (See Figure 3-3.)
Troubleshooting
Refer to the “Battery” information in this section of
the manual for detailed instructions regarding proper
battery maintenance and service procedures. Prior to
troubleshooting the battery equalizer system, inspect
all battery circuit connections for excessive corro-
sion, loose cables, ground connections etc.
Use the following procedure to check the battery
equalizer.
1. Check the circuit breakers.
a. If a circuit breaker has opened, check cir-
cuits and repair cause.
b. Reset circuit breaker.
2. Check battery voltage with the battery equalizer
connected and the engine running.
a. Verify battery charging alternator output is
27.8 to 28.2 volts.
3. If alternator voltage is outside above limits,
adjust voltage regulator as described in “Battery
Charging System”.
4. With the engine running, verify voltages at the
battery equalizer terminals.
a. Measure the voltage between the 24 volt and
12 volt terminals.
b. Measure the voltage between the 12 volt ter-
minal and ground.
5. If the difference between the voltage measure-
ments above exceeds 0.75 volts, the battery
equalizer is defective and should be replaced.
Always open main battery disconnect switch
prior to removing or connecting any wires or
cables in the Battery Equalizer box or prior to
welding on the truck.
1. Battery Equalizer Box Assembly
2. Battery Equalizer
3. Circuit Breaker
4. Circuit Breaker Panel
5. Battery Disconnect Switch
6. Disconnect Switch Handle
7. 12VDC Control Relay
FIGURE 3-3. BATTERY EQUALIZER BOX
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