SECTION J5
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Zener Diode
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The Zener Diode is a semi-conductor device that
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critical but predetermined voltage.
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Assuming the battery is in a low state of
charge, its terminal voltage (the same voltage is
across the diode) will also be low, therefore the
maximum charging current will flow into the battery
from the alternator. At first none of the current
is by-passed by the diode, the latter being
non-conductive due to the low battery terminal
volts. However, as the battery voltage is restored,
the system voltage rises until, at approximately 14
volts, the Zener diode becomes partially
conductive, thereby providing an alternative path
for a small part of the charging current. Small
increases in battery voltage result in large
increases in Zener conductivity until, at
approximately 15 volts, about 5 amperes of the
alternator output is by-passing the battery. The
battery will continue to receive only a portion of
the alternator output as long as the system voltage
is relatively high.
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Depression of the system voltage, due to the use
of 5 headlamp or other lighting equipment, causes
the Zener diode current to decrease and the balance
to be diverted and consumed by the component in
use. If the electrical loading is sufficient to
cause the system voltage to fall below approx. 14
volts, the Zener diode will revert to its high
resistance state of virtual nonconductivity and the
full generated output will go to meet the demands
of the system.
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When refitting a Zener diode, the contact
between the diode and the heatsink must be clean
and free from corrosion. The tightening torque for
the retaining nut is 24-28 Ib./ins. (3.32-3.87
kg/m).
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Testing the Zener Diode
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(a)
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Connect D.C. ammeter between Zener Diode Lucar
Blade and feed cable (Red lead to Zener, Black lead
to cable).
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(b)
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Connect D.C. voltmeter between the Lucar
terminal of the Zener Diode and earth (Red lead to
earth, Black lead to Zener Lucar Blade).
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(c)
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Ensure all lights are switched off and any
accessories unplugged.
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(d)
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Start engine, slowly increase speed and check
meter reading.
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Special Note: THE BATTERY MUST BE IN A FULLY
CHARGED STATE. If the battery condition is poor it
should be temporarily replaced by a known good
battery.
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CURRENT
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DIODE VOLTS
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Nil
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Up to 12.75
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2 Amp
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13.5 to 15.5
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CONCLUSIONS:
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Zener Diode must be replaced if:
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(a)
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Current flow commences before 12.75v is reached.
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(b)
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Voltmeter registers more than 15.5v before 2
amps is shown on the ammeter.
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SECTION J6
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BATTERY
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Lead acid batteries are used on all models. On
Commando models excepting Interpol, a single Lucas
PUZ5A 12 volt battery with transiucent case is
fitted. Later models use Norton Villiers battery
63244 or Yuasa 12N9 4B. On Interpol, two Lucas type
SCZ7E 6 volt batteries are fitted in series. On
both battery types, the acid level can be seen
through the casing and the electrolyte level is
marked clearly on the battery case. A breather vent
is used on both types of battery.
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Battery Maintenance
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Due to continual evaporation and gassing during
charging, a weekly inspection must be made on the
electrolyte level. Since the level will normally
rise whilst the battery is being charged, the level
must only be checked during off-charge periods. Any
loss of electroIyte should be made good by the
addition of distilled water until the level mark is
reached. The level should not exceed this mark, for
spillage may occur with subsequent damage to
surrounding parts.
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It is important to keep the battery connections
clean and tight. Dirt and moisture must be wiped
away from the battery top periodically.
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If the motorcycle is stored for a period, the
battery should be removed and maintained in a good
state of charge every two weeks.
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