Testing Checking Components

Rotor

Resistance measurement
Use an ohmmeter (5 x 1 range) to measure the resistance of the winding between the slip rings.
The resistance should be:
Bosch 80 A 2.5-3.1 Ohm

A low resistance indicates a short circuit in the armature winding. A high resistance (infinity) indicates an open circuit in the armature winding.

Stray current test
Use an ohmmeter (5 x 1000 range) to measure the resistance between one of the slip rings and the generator (stator) frame.

The resistance should be high (infinity).

A low resistance indicates the presence of stray currents between the armature winding and ground.

The stray current test can also be carried out with a 40 V/40 W AC test lamp.

Slip rings
Inspect the surface of the slip rings for grease, dirt and scoring. Clean them with trichloroethylene. Avoid polishing the surface of the slip rings as a highly polished surface makes for poorer contact with the brushes.

The diameter of the slip rings should be 7.8 + 0/-1 mm (1.08 +0/-0.04 in).

The maximum permissible slip-ring ovality is 0.03 mm (0.001 in).






Stator

Resistance measurement
Use an ohmmeter (5 x 1 range) to measure the resistance of the stator windings (three readings).

The resistance should be:
Bosch 80 A 0.10 ± 10% ohms.

Stray current test
Use an ohmmeter (5 x 1000 range) to measure the resistance between the stator frame and each of the stator windings.

The resistance should be high (infinity).

A low resistance indicates the presence of stray currents between the armature winding and ground. The stray current test can also be carried out with a 40 V/40 W AC test lamp.






Diodes (rectifier)
Use a test lamp (up to max. 40 V) or an ohmmeter to test the diodes for an open circuit or short circuit.

1 Positive rectifier diodes
Measure between terminal B+ and the stator connection points.
The test lamp should light up when its positive terminal (max. 40 V) is connected to one of the stator connection points, or the ohmmeter should give a low resistance reading when its positive lead is connected to one of the stator's connection points.
If the connections are reversed, the lamp should not light up, or the ohmmeter should give a high resistance reading (several kohms).

2 Negative rectifier diodes
Measure between terminal D- and the stator connection points.
The test lamp should light up when its positive terminal (max. 40 V) is connected to one of the stator connection points, or the ohmmeter should give a low resistance reading when its positive lead is connected to D-.
If the connections are reversed, the lamp should not light up, or the ohmmeter should give a high resistance reading (several kohms).

3 Excitation diodes
Measure between terminal D+ and the stator connection points.
The test lamp should light up when its positive terminal (max. 40 V) is connected to one of the stator connection points, or the ohmmeter should give a low resistance reading when its positive lead is connected to one of the stator's connection points.
If the connections are reversed, the lamp should not light up, or the ohmmeter should give a high resistance reading (several kohms).






Brush holder
Check that the brushes can move freely in the holder.
Check the wear on the brushes. At least 5 mm (0.2 in) should protrude from the holder.
Check that the brushes are completely insulated from each other. Use an ohmmeter to measure the resistance between the two brushes. The resistance should be high (infinity).
Check that there is good contact between each brush and the "-" and DF terminals.