Z001019/0_6_July 2008 Page ELECTRICAL SYSTEM - 15
06 ELECTRICAL SYSTEM
SERVICE MANUAL MARINE ENGINES
Check rectifier diode
Measuring devices with diode test function will show
the following results:
- in forward direction: voltage drop from 0.4 to 0.6
volt
- in backward direction: reading is "OL".
a) by means of control lamp
Diode and control lamp are connected in series in
both forward and backward direction in an electric
circuit. Diodes permitting passage in both directions
were mostly exposed to excessive voltages. On the
other hand, diodes with an interruption in forward
direction were mostly destroyed by excessive current
or excessive heating.
ill. 04.1 Lamp burning: diode functional.
Lamp not burning: diode interrupted.
ill. 04.2 Lamp not burning: diode functional,
Lamp burning: diode had short circuit.
b) by means of ohmmeter
For diode testing, only a simple, battery-powered
ohmmeter may be used.
Measuring bridges are unsuitable, as they indicate
wrong values. Under no circumstances, hand
generators may be used. Their high voltage would
destroy the diodes. A perfect diode shows a resistance
of only a few ohms (0,5 ...10 Ohm) in forward direction,
but several kiloohms (almost) in backward direction.
+
-
12V
12-V-Lampe
01.04 ill.2
01.04 ill.1
+
-
12V
12-V-Lampe
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