Rothewald 10002567 Mode D'emploi page 51

external field winding. The current is picked up by carbon brushes
at the rotor commutator. This type of generator always runs "dry",
either on the crankshaft stump with an external regulator or as
a separate unit, in which case it will usually have an integrated
regulator. Faults are generally caused by vibrations, by shaking
due to the rotor's transverse acceleration, or by asymmetrical
thermal stresses. The carbon brushes and commutator are subject
to long-term wear. Testing the regulator/rectifier: as described
under 6.1.3. If you intend to test your separate commutator
generator thoroughly, it is advisable to remove it from the bike
(first disconnect the battery) and then dismantle it. Then check the
contact pressure of the brush springs and the length of the carbon
brushes, and replace them if necessary. Clean the commutator
with a suitable solvent (degreaser) and, if necessary, rub it down
with fine sandpaper. Check the depth of the commutator grooves
(approx. 0.5 – 1 mm), recut them with a sawblade if necessary
or replace the rotor if the slip ring has reached its limit of wear.
Insert the red test lead in the VΩmAhFE jack, and the black test
lead in the COM jack on the multimeter. Select the 200 ohm
measuring range, and hold the test probes against each other for
the continuity test until a value of 0.1 to 0.3 ohms is indicated.
Then test for continuity at the stator windings; hold one test probe
in front of and one behind a field winding – a small resistance
should be measured. A high resistance indicates a line break, while
resistance close to zero means that there is a short circuit. To
check for a short circuit to earth, select the measuring range up to
2 MOhms. Hold the red test probe against the stator winding and
the black probe against the housing (earth). The measurement
must show infinite resistance, otherwise there is a short to earth
(fault). Next, measure the resistance between two commutator
bars of the rotor in all possible combinations. There should always
be a low resistance. A value close to zero indicates a short circuit,
while a high resistance indicates a line break requiring the rotor
to be replaced. Select the measuring range up to 2 MOhms on
the multimeter. Hold the red test probe against a commutator bar
and the black probe against the axle (earth). An infinite resistance
must be measured in each case, otherwise there is a short to earth
(rotor fault). Commutator generators mounted on the crankshaft
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