In-Vehicle Testing

Read this carefully before carrying out any tests on the generator or individual components.

Use only a maximum of 40 V DC for testing rectifiers. For insulation and short-circuit tests on the stator and armature windings, use a 40 V/40 W test lamp (do not use a 110 V or 220 V mains supply as this could damage the rectifiers). When measuring the charging current, never disconnect the battery cables while the engine is running.

When soldering or unsoldering diode connections, use flat-nose pliers to hold the diode lead. The pliers will help to conduct the heat away from the semiconductors, which are sensitive to high temperatures (work quickly and use a hot soldering iron).

Avoid bending the leads or applying pressure to them at the point where they enter the rectifier casing.

Before doing any work on the generator, either in the car or on a test bench, always disconnect the battery first.

Important : The generator should be at working temperature (60° C/140° F) during testing.

Testing the generator on a test bench
On the test bench, the generator may only be driven by means of its belt pulley.

Proper cable terminals or plug-in connectors must be used for the electrical connections. This also applies to the battery - makeshift connections should never be used.

During testing, a 12 V battery must be connected in parallel with the generator. The battery serves as a buffer and smooths out the voltage peaks which occur when loads are switched on and off. If such voltage peaks exceed the permissible level, the rectifying effect of the diodes will be destroyed. The maximum voltage for silicon diodes is about 100 V The generator can be tested in generator test benches of most types. In some cases it may be necessary to add suitable mounting and drive arrangements.


WARNING : During testing, the generator must be secured by means of its regular mountings. Clamps and the like should not be used.


Excitation
Unlike a DC generator or dynamo, an alternator is not self-exciting after it has been idle for a lengthier period of time. A 12 V indicator lamp with a rating of about 2 W must therefore be connected to terminals D+ and B+ (see the wiring diagram). The initial excitation current is then applied to the armature field winding via the indicator lamp, generator terminal D+, voltage regulator terminal D+, the closed voltage regulator contacts and terminal DF. Self-excitation starts as soon as the generator voltage opens the excitation diodes, which occurs at 1-2 V. The voltage then rises rapidly and the voltage differential across the indicator lamp decreases. The lamp remains alight until alternator output voltage is equal to battery voltage.

Checking charging capacity
Charging voltage and charging current can be measured with the generator in the car or mounted on a test bench.

Measure the voltage by means of a voltmeter connected to terminal B+ and ground on the generator.

Measure the current by means of an ammeter connected in series with the output lead from terminal B+ on the generator.

Test readings
Connect the battery and apply a load to the generator. Run the generator at the prescribed rated speed. It should then charge at 2/3 of its maximum current:
Bosch 80 A 54 A at 1900 rpm.

Insulation test on assembled generator
After the generator has been dismantled and reassembled, check the insulation between terminal B+ and ground by means of an insulation tester (megger).