Page 50 - Demo

Page 50.Alvis Three Litre Shop Manual - T.A. 21 and T.C. 21DDynamamo Voltag tage RRegugulatator aand Cut ut-out utThe dynamo voltage regulator and the dynamo cut-out are housed in a control box mounted on the bulkhead and are protected by a moulded cover.The regulator causes the dynamo to give an output which varies according to the load on the battery and its state of charge. When the battery is discharged, the dynamo gives a high output so that the battery receives a quick recharge which brings it back to its normal state in the minimum possible time.On the other hand if the battery is fully charged, the dynamo is arranged to give only a trickle charge which is sufficient to keep it in good condition without the possibility of causing damage to the battery by over-charging.The regulator also causes the dynamo to give a controlled boosting charge at the beginning of a run. This quickly restores to the battery the energy taken from it when starting. After about thirty minutes running, the output of the dynamo will have fallen to a steady rate, best suited to the particular state of charge of the battery.The cut-out, which is an automatic switch connected between the dynamo and the battery, allows the current to flow from the dynamo to the battery only. It closes when the dynamo is running fast enough to charge the battery and opens when the speed is low or the engine is stationary, thus preventing current flowing from the battery through the dynamo windings.The cut-out and regulator are accurately set before leaving the Works and need no further attention or adjustment whatsoever.AmmeterThe ammeter on the fascia board indicates the current flowing into or out of the battery, with the exception of the current consumed when the starter motor is in operation, which is much greater than the current used by the rest of the electrical equipment.When noting the ammeter reading it must be remembered that during day time running when the battery is in good condition the dynamo gives only a trickle charge, so that the charge reading will seldom be more than a few amperes.A discharge reading may be given immediately after switching on the head lamps. This usually happens after a long run, when the voltage of the battery is high. After a short time, the battery voltage will fall, and the regulator will respond, causing the dynamo output to balance the load.FusesTwo fuses, indicated by the markings %u2018AUX%u2019 and %u2018AUX IGN%u2019 on the control box cover, protect these accessories which operate irrespective of whether the ignition is switched on or off, and those accessories which operate only when the ignition is switched on. Fuses for the driving lights and other accessories are housed in a separate fuse box.A blown fuse is indicated by the failure of all the units protected by it, and is confirmed by examination of the fuse, which can easily be withdrawn from the spring clips in which it fits. If it has blown, the broken end of the wire will be visible inside the glass tube. Before replacing a blown fuse, inspect the wiring of the units which have failed for evidence of a short circuit, or some other fault which may have caused the fuse to blow, and remedy the cause of the trouble.Spare fuses are provided and it is important to use only the correct replacement fuse. The fusing value is marked on a coloured paper slip inside the glass tube of the fuse.