Starting Motor – Delco 50-MT No Load – Test

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 Test and Adjusting section.

Illustration 1 g00713059

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 four 8 V batteries in series for a 32 V system. Connect eight 8 V batteries in series for a 32 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 following measurements should be observed:

Table 2
No Load Test     24 V     32 V     64 V    
Minimum Voltage     20 V     30 V     32 V    
Minimum Speed     5500 rpm     7500 rpm     5500 rpm    
Maximum Speed     7500 rpm     10,500 rpm     NA    
Minimum Current Draw     95 Amp     100 Amp     NA    
Maximum Current Draw     120 Amp     125 Amp     125 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:

a.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.

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

c.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:

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

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

4.Failure to operate with no current draw indicates:

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

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

c.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:

a.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:

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

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