SECTION 3 - CHASSIS & SCISSOR ARMS
3-36 – JLG Lift – 3121166
3.7 DRIVE MOTOR ELECTRICAL
EVALUATION
Several basic electrical tests can be performed on the
Drive Motors. Failure of one of these evaluations is signifi-
cant and may indicate that the device is physically dam-
aged.
Refer to Figure 7-2., Resistance Measurement. Disconnect
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 resistance can signal
corrosion, improper crimps, damaged 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 measure-
ment, 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-circuit for an ordinary
voltmeter. High resistance can signal corrosion,
improper crimps, damaged connectors, 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 cor-
rosion, improper crimps, damaged cabling, or a faulty
solenoid.
• Resistance > 1 MegaOhms Red Armature Wire to
Motor Housing. The armature winding should be elec-
trically isolated from the motor housing. Low resistance
may be an indication of a crushed cable, a burned
cable, or a burned armature winding. Investigate 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 elec-
trically 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 discon-
necting 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. Investigate
by disconnecting the drive motor cable from the motor
and re-measure resistance (isolation).
Servicing Guidelines
Since the operating environment of industrial equipment
varies widely, the following are suggested for periodic
maintenance inspection intervals.
• Normal Service – Perform routine inspection (outlined
in the Inspection and Service portion of this section)
every 1,000 hours of drive time.
• Severe Service – Perform routine inspection every 500
hours of drive time. Severe service environments are
listed below:
a. Dusty or dirty locations like cement plants, lum-
ber and flour mills, coal mining, stone quarries,
etc.
b. High temperature areas like steel mills, found-
ries, etc.
c. Environments with sudden temperature change,
such as in refrigeration plant, etc.
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