Service manual

DCB, DCFCB and DCFCTB Models

Theory of Operation

above the 10 Volt threshold. Current is applied until the battery voltage rises to

13.5 Volts.

Float Charge

The float charge is entered when the battery voltages reaches 13.5 Volts. The

battery voltage is held at 13.5 Volts. While in the float state, the charger supplies

up to 4 Amps to a load and the battery. The charger remains in the float/bulk

charge state until the battery voltage drops below 9 Volts.

Voltage Regulator

Voltage entering from the transformer is converted to full-wave rectified D.C. by

D9. This yields 120 positive going voltage peaks a second. Through resistor

divider R17 and R18, U3-A compares the battery voltage to that of U5, a 5 Volt

reference. If the battery voltage is less than 13.5 Volts, the output of U3-A goes

high turning on Q5. This turns on SCR D3 allowing the one voltage peak to pass

to the battery helping to raise its voltage. When the voltage peak falls back below

that of the battery, the current through D3 drops to zero and D3 turns off. U3-A

continuously sends voltage peaks to the battery until its voltage reaches 13.5 V.

Current Limiter

U1-A monitors the current output of the charger by watching the voltage

developed across R24. If the current rises above 4 Amps, the output of U1-A

rises, turning on Q2. This temporarily prevents U3-A from sending any peaks of

voltage to the battery through D3 and reduces the current output.

U1-B monitors the battery’s voltage. If it is below 10 Volts, the output of U1-B

goes high turning on Q3 and pulling R6 to ground. This changes the current

limiter’s threshold from 4 Amps to 2 Amps.

Thermal Limiter

U2 monitors the temperature of the PC board. If the temp exceeds 105°C, the

output of U2 goes high. This turns on Q1 and pulls R6 to ground. This limits the

charge current to 2 Amps rather than 4 to help prevent the charger from

overheating.