stator / alternator

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If the battery goes on strike Check the charging circuit on the motorcycle.
Most motorcycles draw power for lights, starter, ignition, etc. from the battery. Without sufficient battery voltage, the vehicles are no longer roadworthy. An empty battery can have several causes 
Battery defective ( layer short circuit )
The battery is not sufficiently charged during driving.
A leakage current ( insulation damage ) or a consumer draws current.

How do I recognize a weak battery in good time?

The charge indicator lamp lights up.
The starter motor turns slowly.
Light becomes dimmer while driving

Fault location

First check the battery charging circuit on the motorcycle:
Battery terminals and + and - leads must not be corroded.
Check plug connections of regulator and alternator. They should be clean and tight.
Wires must not show signs of breakage, abrasion, burns or corrosion. 
Check regulator/rectifier for visible mechanical defects.
Always check the complete battery charging circuit! ( Even if a fault has already been found).

For the following tests, the motorcycle battery should be charged and in good condition.

Measuring the charging voltage

It is necessary to check the alternator.

1. Checking an alternator with permanent magnet rotor.

Permanent magnet rotors operate in star alternators.
By rotating the rotor, a voltage is induced in the windings of the stator. The rotor is often mounted on the crankshaft journal and runs in an oil bath. Defects occur due to overheating and due to overloading of the controller.

Resistance measurements can be used to detect the faults.
Carry out an ohm measurement with the ignition switched off. Clamp the negative cable to ground and measure all contacts of the alternator connector with the other test probe. The resistance measurement must be infinite ( no continuity ). If resistance is measured, the stator has a ground fault and is defective.
The next resistance measurements are to measure the contacts ( coils ) against each other.  The measured resistance should give similar values for all 3 measurements. Usually below 1 Ohm ( see specifications in the workshop manual ). Deviating measurements e.g. 0 Ohm means short circuit and with higher resistance value than the other comparison measurements indicate a fault in the winding. Both measurements indicate that the stator is defective.
If no faults are found in the resistance measurements and the alternator voltage is too low it may be due to the demagnetized rotor. (Permanent magnets are subject to aging).

2. Testing a collector alternator

In contrast to the previously measured alternator with permanent magnet, the collector alternator induces the current with the aid of an external electromagnet. The current is tapped at the collector of the rotor via collector brushes. Collector alternators are usually flanged to the engine. The regulator is often integrated in the alternator. External regulators are also used for alternators that operate on the crankshaft stub.
Faults and insufficient alternator output can be caused by vibrations, high temperature and worn carbon brushes or worn collectors.
To check the alternator, it is advisable to remove it from the engine and disassemble it. Do not forget to disconnect the battery first!

Fault location / rectification:

Check length of carbon brushes (replace worn parts),
Check pressure force of brush springs, 
Clean / degrease collector with gasoline or brake cleaner.
Remove collector with fine abrasive paper
collector grooves should be approx. 0.5 - 1 mm
if necessary, re-cut with saw blade or if the wear limit of the slip ring is reached - replace rotor

Checking the stator winding

1. measurement
The field windings by resistance measurement. Connect the measuring strip before and after each field winding. The measured values should be similar (less than 1 Ohm, compare measured value with original value from workshop book). If the measured value is too high, there is an interruption.
2. measurement
Select resistance measurement in high ohm range and hold + test probe to stator winding connect - test probe to ground. Measured value must be infinite. Otherwise the stator has a ground fault.
3. measurement
Resistance measurement between the collector lamellas of the rotor. Measure all lamellas against each other. Measured value approx. 2 - 4 Ohm. Compare measured values with information in the workshop manual. At 0 Ohm - short circuit, measured value too high - interruption.  If rotor is defective, replace it. 
4. measurement
Select high ohmic range for rotor resistance measurement, connect + wire from multimeter to the respective collector lamella and the - wire to ground (e.g. axle).  Measured value must be infinite. Otherwise the stator has a short circuit to ground. Rotor must be replaced.

Collector alternators which are mounted on the crankshaft stub must be uncovered.
Disconnect motorcycle battery before!
Check collector, rotor and stator. Insufficient alternator output can be caused by defective pressure springs, worn carbons or an oily collector. If the collector is wet or oily, check the sealing. 
Check the rotor windings by measuring between the copper tracks of the collector (measured value approx. 2 - 6 Ohm). Compare measured value with specification in workshop book. Measured value 0 means short circuit, if the measured value is too high, there is a winding break. The measurement against ground must result in an infinitely high resistance. Otherwise there is a short circuit to ground.
Exactly as described for the external collector alternator, the stator windings are measured for continuity and ground short-circuit at the cable connections.