Section 5. Troubleshooting
Model 5200 High-Level Orderpicker
Electric Motor Tests
Open Circuit Motor Test An open circuit is one where the electrical circuit within the motor has been broken. This can be caused by: • Bad brushes or brush springs • Broken wire in the field or armature winding • Loose or bad connection Refer to Figure 5-3 for the following procedure: 1. Isolate the motor from the lift truck circuit by removing the power cables. Use two wrenches to avoid twisting the terminal stud. 2. With the motor at room temperature, connect the leads of a digital ohmmeter between the individual circuits in the motor. 3. You should observe the following measurements: Table 5-2: Motor
Probe Points
Resistance
Traction Motor
S1 to S2 (shunt)
0.9 to 1.5 ohms
S1 to S2 (series)
< 1 ohm
Lift Motor
Steer Motor
A1 to A2
< 1 ohm
A1 to S1; A1 to S2
> 100,000 ohms
A2 to S1; A2 to S2
> 100,000 ohms
A1 or A2 to Frame
> 100,000 ohms
A to S
< 1 ohm
A to Frame
> 100,000 ohms
A1 to A2
< 1 ohm
A1 or A2 to Frame
> 100,000 ohms
4. If the meter indicates high resistance in the armature, check the condition of the brushes before replacing the motor.
5-12
5. If you find an open circuit in a series-wound motor, the motor must be disassembled by a motor rebuilding facility to isolate the problem to the field or armature circuit.
Grounded Motor Test In a grounded motor, an electrical circuit exists between the current-carrying conductors and the motor housing. This can be caused either by direct contact or through conductive foreign material. The ground may be caused by: •
Insulation breakdown
•
Brush leads touching the motor housing
•
Buildup of carbon dust or other materials
To test for a grounded motor, see “Shorts to Frame” on page 5-2.
Short-Circuited Armature or Field Winding A short circuited winding is one where the insulation on the field or armature has broken down at two or more points. The breakdown creates a low resistance path, allowing current to flow from one turn of the coil to another adjacent coil turn, without actually flowing through the coil wire. The result is a decrease in total resistance of the motor winding and an increase in the current flow. The severity of the short circuit depends on its location. A shorted motor may be indicated by: •
Slow or sluggish operation
•
Running faster than normal (suggests a short in the field)
•
Overheating
•
Blowing a power fuse
•
Burning of brush wires
•
Severe burning or discoloration on the armature coil
•
Severe burning or discoloration on one or two commutator segments every 90° of rotation
Publication Number: 1043922B, Revised: 2 Sept 2015
