Norton Commando Workshop Manual

## Electrical

# J

### SECTION J5

### Zener Diode

The Zener Diode is a semi-conductor device that | becomes conductive in the reverse direction at a critical but predetermined voltage.
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.
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.
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).

### Testing the Zener Diode

(a) | Connect D.C. ammeter between Zener Diode Lucar Blade and feed cable (Red lead to Zener, Black lead to cable).
(b) | Connect D.C. voltmeter between the Lucar terminal of the Zener Diode and earth (Red lead to earth, Black lead to Zener Lucar Blade).
(c) | Ensure all lights are switched off and any accessories unplugged.
(d) | Start engine, slowly increase speed and check meter reading.

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.

CURRENT | DIODE VOLTS
Nil | Up to 12.75
2 Amp | 13.5 to 15.5

### CONCLUSIONS:

Zener Diode must be replaced if:
(a) | Current flow commences before 12.75v is reached.
(b) | Voltmeter registers more than 15.5v before 2 amps is shown on the ammeter.

### SECTION J6

### BATTERY

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.

### Battery Maintenance

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.
It is important to keep the battery connections clean and tight. Dirt and moisture must be wiped away from the battery top periodically.
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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