Instructions For Manual Control Of Generators; Trouble Shooting And Repairs; Electric Anomaly - MarelliMotori MJB 160 Nstrucciones Y Advertencias De Seguridad

6.3 Instructions for manual control of generators

If the voltage regulator (AVR) breaks down, a manual control system can be used, when a 24 V D.C. power supply
is available.
This source could consist of a bank of batteries or of a voltage transformer and a rectifier unit connected at the alternator
output.
- disconnect the two exciter stator terminals ( whites wire + and -) from AVR;
- apply the D.C. power supply to these two wires;
- set the rheostat R to adjust the alternator output voltage.
ATTENTION! Compensate by manually increasing excitation as the load increases.
Before removing the load, reduce the excitation current.
Use the following table to select the rheostat:
MJB 160 – 200

7. TROUBLE SHOOTING AND REPAIRS

7.1 Electric anomaly

TROUBLE
The alternator will not
energise (no load voltage
below 10% of rated
voltage).
The alternator will not
energise (no load voltage
20-30% of rated voltage).
Voltage insensitive to
AVR potentiometer's
rotation.
Voltage lower then rated
(output voltage between
50 and 70%).
Voltage too high.
Unstable voltage.
SIN.UM.805.6
WHITE
EXCITER
STATOR
W I N D I N G
T E R M I N A L S
WHITE
Generator
POSSIBLE CAUSE
a) Loose connections.
b) Rotating diodes or surge suppressor
broken.
c) Excitation circuit shorted or interrupted.
d) Insufficient residual voltage.
a) Fuse (on AVR's supply line) blown.
b) Connection's cut on the exciter stator.
c) Incorrect connections of exciter stator.
a) Speed less than rated.
b) Voltage potentiometer unset.
c) Fuse blown.
d) Faulty regulator.
e) Overexcitation limitation intervention.
a) Potentiometer V unset.
b) Faulty regulator.
a) Diesel engine rpm variations.
b) Stability potentiometer unset.
c) Faulty regulator.
24 V
R
I max
[A]
5
REMEDY
(always to be done with the machine switched off)
a) Check and repair.
b) Check the diodes and change in case they are open or
short circuited.
c) Check the continuity and repair.
d) Apply for a while a 12 Volt battery voltage connecting
the – terminal to – of AVR and + terminal to + of AVR by
means of a diode.
a) Replace the fuse with the spare. If the fuse blows again
check if the exciter stator is short circuited. If everything is
correct, change the AVR .
b) Check the continuity and repair.
c) Reverse the two wires from the exciter stator.
a) Check rpm (frequency).
b) Rotate the potentiometer until the voltage reaches the
rated value.
c) Replace the fuse with spare.
d) Disconnect AVR and replace it.
e) Re-set the potentiometer for excitation limitation (AMP).
a) Rotate the potentiometer until the voltage reaches the
rated value.
b) Replace AVR.
a) Check rpm uniformity. Check the diesel engine
governor.
b) Act on AVR's stability potentiometer.
c) Replace AVR.
13
ENGLISH
Max. resistance of rheostat
[Ω]
80
963857153_F