37-MT, 41-MT, and 42-MT Series Starting Motors Caterpillar

The following procedure is used in order to perform the no-load test after the starting motor has been repaired. The test should also be performed when the starting motor is removed from the machine. In order to check a starting motor completely, the complete procedure should be followed. To check the starting motor components, refer to the Testing and Adjusting section.

Illustration 1	g02718921
No load test diagram (24V)

1. Illustration 1 shows a 24 V system with two 12 V batteries that are connected in series to a starting motor. Connect one 12 V battery for a 12 V system. Connect the positive side of the battery cable to the "BAT" terminal of the starting motor solenoid. Connect the negative side of the battery cable to the negative terminal of the starting motor.

2. As shown, connect an open switch between the "S" terminal and the "BAT" terminal of the solenoid.

3. Connect the multimeter red lead to the "Mtr" terminal on the solenoid. Connect the multimeter black lead to the negative terminal of the starting motor.

4. Use a phototach or a rpm indicator in order to measure the speed of the armature.

5. Close the switch. The measurements in Table 2 should be observed:
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   Table 2

   No Load Test	37-MT 12 V	37-MT 24 V	41-MT 12 V	41-MT 24 V	42-MT 12 V	42-MT 24 V
   Minimum Voltage	11 V	23 V	11 V	23 V	11 V	23 V
   Minimum Speed	5501 rpm	3215 rpm	5501 rpm	7200 rpm	5100 rpm	5960 rpm
   Maximum Speed	8535 rpm	4041 rpm	8535 rpm	9700 rpm	8700 rpm	9326 rpm
   Minimum Current Draw	100 Amp	68 Amp	100 Amp	68 Amp	100 Amp	68 Amp
   Maximum Current Draw	155 Amp	100 Amp	155 Amp	100 Amp	155 Amp	100 Amp

6. If the voltage is below the minimum, the batteries are low and the batteries need charged.

   Note: If the voltage is higher, the speed will be proportionally higher.

No Load Test Results

The following information provides some results of a no-load test and the possible problems.

1. A rated current draw at a no-load speed indicates a normal starting motor.

2. A low free speed and a high current draw indicate:

   1. An increase in friction could be caused by tight bearings, dirty bearings, or worn bearings. A bent armature or loose field pole shoes that would allow the armature to drag are possible causes of increased friction.

   2. A shorted armature could cause a high current draw. A shorted armature can be checked on a growler tester after disassembly.

   3. A grounded armature or a grounded field winding could cause a high current draw. Check for grounds after disassembly.

3. Failure to operate with a high current draw indicates:

   1. A direct ground in the terminal or field windings.

   2. The bearings cease to operate properly. The bearings can be seen by turning the armature by hand.

4. Failure to operate with no current draw indicates:

   1. An open field circuit will cause a failure. The system can be checked for an open field circuit with a multimeter after disassembly.

   2. An open armature will cause a failure. Inspect the commutator for badly burned bars.

   3. Broken brush springs, worn brushes, or high insulation between the commutator bars could prevent good contact between the brushes and the commutator.

5. A low no-load speed and a low current draw indicate:

   1. An internal resistance that is high is possibly caused by poor connections, leads that are faulty, a commutator that is dirty, and/or causes that are listed in step 4.

6. A high free speed and a high current draw indicate:

   1. A shorted field circuit will cause a failure. Check the field winding for shorts after disassembly.