Is Your CAR BATTERY OK ? Then check your alternator

test the car battery first then the alternator.

Many of our customers have had problems with their car not starting, this usually happens on freezing winter mornings. The usual cause lies with a dead car battery and once changed the problem may be solved.

Some motorists though start have the same problem a few more mornings after the car battery has been fitted and usually come marching back to the place where they bought the new car battery claiming that the battery may be faulty. Car owners usually calls us shouting expletives about” how rubbish “our batteries are. We calm them down and recover their car back to our auto centre where we can test the charging system for a faulty alternator.

The first thing we do is to check the alternators charging voltage, we use a hand held portable computer tester for this job. We measure the voltage of the battery with a voltmeter setting with the engine running. It should give a reading of between 13.5 and 14.5 volts. If the reading is below these voltage figures we can suspect that the alternator is at fault and will need replacing.

The alternator gets its name from the fact that it generates “alternating” current known as (AC). Batteries can only use direct current (DC), so the current from the alternator is transferred from AC to DC through what are called “diodes”. The alternator is able to give out a high voltage when the car is running slowly. Your alternator is really three alternators in one. The three sections generate their own voltage out of step with the other two parts.

Therefore in one revolution the alternator puts out three separate voltages. Each three sections of the alternator has its own windings and diodes, either of these components can fail in service one part at a time, but the alternator can still give out a charge into the battery, if one part fails the other parts may still function, this may enable the alternator to carry on in a limited way for a long period before finally failing.

Battery and alternator now fixed means a  pleased customer ?

The failing alternator is usually found out in freezing conditions in the middle of winter when your heater/wipers/lights are needed at full pelt on a cold winters morning. Hope this gives my customers some insight to the workings of your cars alternator.