Car Components Electrical Systems 

Replacing dynamo brushes

Undo the screws holding the brush cables. The carbon brushes are a sliding fit in oblong holders on the dynamo endplate. Coiled springs bear against the tops of the brushes to hold them in contact with the commutator. Each brush also has a braided wire or cable attached by a screw. The cable from one brush leads to earth, and that from the other to the dynamo output terminal. Undo the screws holding the cables, push the ends of the coiled springs to one side of the brush holders, and…

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Car Components Electrical Systems 

How to fix a dynamo

The electrical connections from a dynamo are on the rear endplate. Current generated in the armature is passed through the commutator to spring-loaded brushes and thence to terminals on the endplate. Wear on the carbon brushes and commutator is the most common cause of dynamo failure. Normally the brushes wear first, but as they become smaller the spring pressure holding them in contact with the commutator weakens. This leads eventually to continuous sparking – known as arcing – between brushes and commutator. Arcing causes rapid wear on the commutator, pitting…

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Car Components Electrical Systems 

Testing an alternator and checking output

Prise off the flexi-cover with a small screwdriver. Alternators have replaced dynamos as generators on modern cars; they can produce more current. Any short or open circuit or wrong connection can cause a sudden surge of voltage that will damage electronic parts. Never make or break any connection while the engine is running. Checking alternator output using an ammeter in series with the charging system should be done only by an auto-electrician. A safe test can be made with an induction ammeter held parallel to the output cable, but it…

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Car Components Electrical Systems 

Checking, adjusting and refitting drive belts

The belt runs in V-pulleys and drives the generator and water pump, with its fan, from the crankshaft pulley. Drive belts always stretch a little in use, because of the strains put on them by driving the water pump and generator, as well as the fan itself if it is in the system. Age and continual flexing also cause belts to crack and deteriorate. Stretching slackens a belt, so that it slips on the pulleys. A cracked belt will eventually break. The tension and general condition of the belt should…

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Car Components Electrical Systems 

Using a car battery charger

An average car battery has a capacity of around 48 amp hours which means that, fully charged, it delivers 1 amp for 48 hours, 2 amps for 24 hours, 8 amps for 6 hours and so on. A basic charger usually charges at around 2 amps – and so needs 24 hours to deliver the 48 amps needed to fully charge a flat, 48 amp hour battery. But there is a wide range of chargers with different charge rates on the market – from 2 to 10 amps. The higher…

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Electrical Systems Car Components 

Checking the batteries

Most car batteries are sealed for life – apart from a small vent hole which allows gas to escape. They never need topping up. The fluid level in other batteries should be checked at least once a month and topped up if it drops below the correct level – just above the tops of the battery plates. Never top up with tap water, which contains minerals which may damage the battery. Use distilled or otherwise purified water, or a proprietary topping-up fluid. Avoid over-filling, which causes the electrolyte to leak…

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Car Components Electrical Systems 

Testing a dynamo and checking output

The dynamo is a simple direct-current generator with two output terminals. The dynamo is a robust and simple type of generator which was fitted to many earlier cars. Most modern cars are fitted with an alternator. If you suspect a fault in the dynamo, check all the connections to it with a circuit tester. Check also that the dynamo actually turns when the engine is running, and that the drive belt is adjusted to its correct tension, and is not slipping (See Checking, adjusting and refitting drive belts). Checking output…

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testing-a-dynamo-and-checking-output Car Components Electrical Systems 

how to Test a dynamo and check output

The generator is a robust and simple type of generator installed in many early cars. Most modern cars are equipped with an alternator. If for some reason you suspect a generator failure, be sure to check all connected circuit testers. Check that the generator is also actually running when the engine is running and the transmission belt is adjusted to the correct tension and does not slip. Checking output with a voltmeter or tester Make these checks with a voltmeter if possible. If not, use a circuit tester or test…

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