Model 9600/9700 Swing-Reach ® Lift Truck

3.Observe the following measurements:

Short Circuited Ar mature or Field Winding

4.If the meter indicates high resistance in the armature, check the condition of the brushes before replacing the motor.

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

•build-up of carbon dust or other materials

Isolate the motor from the lift truck circuit by removing the power cables. Use two wrenches to avoid twisting the terminal studs.

Attach one lead of a megohm meter or a digital ohmmeter to a motor terminal and the other lead to an unpainted surface of the motor housing. Set the ohmmeter to the highest scale.

If the ohmmeter reads resistance of <100,000ohms, the motor is grounded. Clean, repair, or replace the motor as necessary.

A short circuited winding is one that 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 usual (suggests a short in the field)

•Overheating

•Blowing a power fuse

•Burning of brush wires

•Severe burning or discoloration on armature coil

•Severe burning or discoloration on one or two commutator segme nts every 90° of rotation.

These symptoms can be caused by problems other than the motor itself, such as binding in a related pump, hose, or solenoid valve.

Testing a motor for short circuited windings requires special equipment at a motor rebuilding facility.

Publication: 1089040, Issued: 08 Apr 2016

Section 5.Troubleshooting

Model 9600/9700 Swing-Reach ® Lift Truck

AC Motors

AC motors used on this lift truck are brushless, 3-phase, internally delta-connected, variable speed motors.

The AC motor has a rotor (in place of the DC armature) and a stator (in place of the DC field). There is no electrical connection to the rotor; current is induced in the rotor. The stator has three windings staggered 120° apart, and three external connections labeled U, V, and W. See Figure5-10.

Open Winding

If the AC motor fails with an open winding, the motor moves erratically, as if hunting/ searching, and there is a ticking sound. Rotation is much slower than usual.

Using a clamping ammeter, measure current in each of the motor power cables. The open phase reads significantly lower than the other two phases.

Shorted Winding

If the AC motor fails with a shorted winding, the motor moves erratically, as if hunting/ searching, and there is a high-pitched sound.

Using a clamping ammeter, measure current in each of the motor power cables. The shorted phase reads significantly higher than the other two phases.

Electrical Troubleshooting 5-20

Publication: 1089040, Issued: 08 Apr 2016