Doosan D20G, Service Manual

Page: 617 / 1209

G424F(FE) Service Manual Chapter 4. Engine Electrical System 117
The result of these switches and relays is to permit a
5 amp dash-mounted switch to turn on a 500 to
1000amp motor used to crank an engine. Battery
voltage (power) available during cranking varies
according to the temperature of the batteries. The
following chart is a guide as to what to expect from a
normal system.
TYPICALSYSTEM VOLTAGE DURING
CRANKING AT VARIOUS AMBIENT
TEMPERATURES
Temperature 12V System
-23 to -7 C (-10 to 20 F) 6 to 8 Volts
-7 to 10 C (20 to 50 F) 7 to 9 Volts
10 to 27 C (50 to 80 F) 8 to 10 Volts
Figure 1
The next chart shows maximum acceptable voltage
loss in the high current battery circuit feeding the
starting motor. These values are maximums for
machines of approximately 2000 SMH and up.
Newer machines would be less than those shown.
MAXIMUM ACCEPTABLE SYSTEM VOLTAGE
DROPS DURING CRANKING
Circuit 12V System
Battery(-) post to starting motor (-)
terminal
0.7 Volts
Battery (+) post to solenoid (+)
terminal
0.5 Volts
Solenoid Bat terminal to solenoid
Mtr terminal
0.4 Volts
Figure 2
Voltages greater than those shown are most often
caused by loose and/or corroded connections or
defective switch contacts.
Diagnosis Procedure
TOOLS NEEDED
Digital Multimeter or Equivalent 1
DC Clamp-On Ammeter or Equivalent 1
NOTICE
Do not operate the starting motor for more than
30seconds at a time. After 30 seconds, the cranking
must be stopped for two minutes to allow the
starting motor to cool. This will prevent damage to
the starting motor due to excessive heat buildup.
If the starting motor cranks real slow or does not
crank at all, do the following procedure:
1.
Measure battery voltage at the battery posts with
the multimeter while cranking or attempting to
crank the engine. Make sure to measure the
battery posts. Do not measure the cable post
clamps.
2.
Is battery voltage equal to or greater than shown
in Figure 1?
• If the battery voltage is correct, go to Step 3.
• If the battery voltage is too low, Charge or
replace the battery.
NOTE:
Alow battery can be caused by battery
condition or a shorted starting motor.
3.
Measure current draw on the (+) battery cable
between the battery and the starting motor
solenoid with the clamp-on ammeter. The
maximum current draw allowed is 350 Amp. At
temperatures below27°C (80°F), the voltage will
be less and the current draw will be higer. If
current draw is too much, the starting motor has a
problem and must be removed for repair or
replacement.
NOTE:
If voltage at the battery post is within
approximately 2 volts of the lowest value in the
applicable temperature range of Figure1 and if the
large starting motor cables get hot, then the starting
motor has a problem and the Ammeter test is not
needed.
4.
Measure starting motor voltage from test point (4)
to (5) with the multimeter while cranking or
attempting to crank the engine.