BOSS 2S8651 - Caterpillar

Table 2
Polarization Index     Winding State     Action    
Less than 1.5     Poor/Failing     Clean the generator set and dry the generator set. Refer to Special Instruction, SEHS9124, "Cleaning and Drying of Electric Set Generators".    
Between 1.5 and 2.0     Marginal     Increase the monitoring frequency to monthly.    
Over 2.0     Good     Maintain the recommended tests per the Operation and Maintenace Manual of the Product.    
Measure the resistance of the exciter stator windings. If the measurements are outside the values that are listed below, the exciter stator is faulty. Repair the windings or replace the windings. Refer to the following measurements:5000 Series (Generator Serial Number (S/N: L5B; G5B) ) ... 8.5 ohms to 10.6 ohms6100 Series (Generator Serial Number (S/N: L6B; G5B) ) ... 9.0 ohms to 11.0 ohms7000 Series (Generator Serial Number (S/N: L7B; G5B) ) ... 10.8 ohms to 13.2 ohmsMoisture
Always make sure that the generator and the controls have been thoroughly dried before you place the items into service. A standard generator set control panel and generator connection box is designed to prevent rain water ingress. However, when the generator set is subjected to pressure washing during the routine maintenance, there is the danger that water may enter the terminal box. This is especially true if the water stream is applied at directions other than from directly above the generator. The subsequent operation of the generator may lead to failures of the Voltage Regulator.Loss of Magnetism
In certain situations the generator residual magnetism may be lost. Field flashing is recommended in this case. However, to avoid permanently damaging the Voltage Regulator, it is essential that the battery power polarity that is used for the field flashing is correct. The positive side of the battery must be connected to E+. The negative side of the battery must be connected to E-.Proper Connections
The generator set must not be started or the generator set must not be run under the following conditions:
Wire E+ and wire E- are not connected to the Voltage Regulator.
Available power inputs (X1, X2, Z1, Z2) are connected to the Voltage Regulator.Additional Troubleshooting Information
Table 3
Fault     Action     Effect     Check/Cause    
No voltage at no load on start up.     Flash the exciter stator: Using either a 6 Vdc battery or a 12 Vdc battery, connect battery positive to E+ and battery negative to E- for 2 to 3 seconds when the engine is stopped. Then restart generator set.     When restarted, the alternator builds up its correct voltage.     Problem was lack of residual magnetism, for Self-excited or AREP generators.    
When restarted, the alternator provides no voltage or does not reach the rated voltage. Check the power connections X1, X2, Z1, Z2 to the AVR
Check exciter stator wiring/resistance
Check main rotor resistance
Check diodes
Check armature (main stator) for short-circuit    
Voltage too low     Adjust the voltage potentiometer (P2) or the remote voltage adjust potentiometer.
Stop the generator set.
Restart the generator set.
Check the voltage again.