SECTION 3 - CHASSIS & SCISSOR ARMS
3-4
31215074
3.3
DRIVE MOTOR ELECTRICAL EVALUATION
Several basic electrical tests can be performed on the
Drive Motors. Failure of one of these evaluations is sig
-
nificant and may indicate that the device is physically
damaged.
Refer to Figure 7-2., Resistance Measurement. Discon
-
nect the Main Battery Disconnect and all drive motor
cables during this analysis.
•
Resistance < 2 Ohms Red to Black Armature Wires.
The heavy red and black conductors are connected
to the motor's armature winding. The winding is a
very low impedance and should appear to be a
short-circuit for an ordinary voltmeter. High resis
-
tance can signal corrosion, improper crimps, dam
-
aged cabling, worn brushes, a faulty commutator, or
an open armature winding.
•
Resistance < 2 Ohms Blue to Orange Field Wires.
The blue and orange conductors are connected to
the motor's field winding. In order to make this mea
-
surement, it will be necessary to disconnect the butt-
splice on the two orange wires or use a piercing
meter probe. As with the armature, the field is a very
low impedance and should appear to be a short-cir
-
cuit for an ordinary voltmeter. High resistance can
signal corrosion, improper crimps, damaged connec
-
tors, damaged cabling, or an open field winding.
•
Resistance 15-25 Ohms Yellow to Brown Brake
Wires.
The yellow and brown wires are connected to
the integral brake. Improper resistance can signal
corrosion, improper crimps, damaged cabling, or a
faulty solenoid.
•
Resistance > 1 MegaOhms Red Armature Wire to
Motor Housing.
The armature winding should be
electrically isolated from the motor housing. Low
resistance may be an indication of a crushed cable, a
burned cable, or a burned armature winding. Investi
-
gate by disconnecting the drive motor cable from
the motor and re-measure resistance (isolation).
•
Resistance > 1 MegaOhms Blue Field Wire to
Motor Housing.
The field winding should also be
electrically isolated from the motor housing. Low
resistance may be an indication of a crushed cable, a
burned cable, or a burned field winding. Investigate
by disconnecting the drive motor cable from the
motor and re-measure resistance (isolation).
•
Resistance > 1 MegaOhms Red Armature Wire to
Blue Field Wire.
The armature and field windings
should also be electrically isolated from one another.
Low resistance may be an indication of a crushed
cable, a burned cable, damaged windings. Investi
-
gate by disconnecting the drive motor cable from
the motor and re-measure resistance (isolation).
Common Traction System Difficulties
1. Short-Circuit Motor Armature
This issue will allow the vehicle to drive very slowly
or not at all. Rapid motor overheating (one motor)
will result.
This situation can be detected by elevating the
vehicle's front wheels and engaging drive (plat
-
form stowed). Under DIAGNOSTICS - TRACTION,
the JLG Analyzer's ARM CUR display (Armature
Current Reading) will exceed 120A. The FLD CUR
display (Field Current Reading) will hover around
40A. Neither wheel will rotate at normal speed, but
it will be possible to rotate the drive wheel by
hand. The Power Module's self-diagnostics cannot
detect this fault since the situation appears identi
-
cal to climbing a steep grade.
To find the source of the difficulty, pull the Main
Battery Disconnect and disconnect the Armature
Wiring (heavy red and black conductors) from the
suspected drive motor leading to the Power Mod
-
ule's M1 and M2 Terminals. Re-test the traction
function. If the remaining drive motor is able to
reach full speed (and Armature Current is less than
50A), the drive motor that has been disconnected
is fault. Investigate for crushed and burned cables.
Note if the drive motor smells burned.
2. Short-Circuit Brake Release
This issue will not allow the vehicle to drive. Rapid
motor overheating (both motors) will result. Con
-
tinued attempts to drive the vehicle may result in
armature damage.
This situation can be detected by elevating the
vehicle's front wheels and engaging drive (plat
-
form stowed). Under DIAGNOSTICS - TRACTION,
the JLG Analyzer's ARM CUR display (Armature
Current Reading) will exceed 120A. The FLD CUR
display (Field Current Reading) will hover around
40A. Neither wheel will rotate, and it will be impos
-
sible to rotate either drive wheel by hand. The
Ground Module cannot detect this fault during
power-up or self-test since energizing the brakes
could pose a hazard. However, it may detect this
issue during Drive (investigate using JLG Analyzer).
To find the source of the difficulty, remove the rear
cover from either drive motor. Insert voltmeter
leads into the white connector leading to the
brake solenoid (yellow and brown wires) and
attempt to drive (Platform Mode). The Ground
Module will apply approximately 24V to the brake
release solenoids (wired in parallel) during drive,
but will reduce this voltage in the event of a short-
circuit. If this voltage is improper (less than 8V),
investigate using resistance measurement (refer to
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