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Car Alternator.
The car alternator is used to charge the car battery when
the engine is running and is a perishable item on a car
which can fail after many miles of motoring. When the
alternator fails usually the battery light will come on
on the display to indicate the battery is no longer
charging.
Alternator on petrol cars.
On a petrol car the alternator is more crucial than on a
diesel car as the battery provides the power for the
spark therefore if a battery is not charging the battery
will eventually flatten and no spark will be generated
causing engine failure.
Alternator on diesel Cars.
Although the diesel car needs a battery for electrical
items such as lights, indicators, radio, fans, rear
demist, windscreen wipers...etc, once the engine is
running it does not need electrical power to keep
running. In the event of an alternator failure you would
not be stranded by a engine shut down but safety would
be compromised by loss of signalling and lights.
Testing your alternator.
Testing your alternator is a quick and simple. You don't
need to remove the alternator to carry out a test and it
doesn't require expensive tools.
What you will need is a volt meter or multi meter. They
are very simple to use, and can be purchased in many
retailers for as little as £5.
Alternator Test.
Make sure all the electrical items mentioned above are
turned off and then have someone rev the car's engine to
a fast idle (say 2000-2500 rpm).
Set the Voltmeter to DC and place the red lead of the
voltmeter on the positive terminal and black lead on the
negative terminal of the battery.
At a fast idle, the voltage should read approximately 14
volts (13.5 to 14.4). Although your battery will be
likely 12 volt the alternator has to generate a larger
voltage to overcome the internal resistance of the
battery. The current needed to recharge the battery
would not flow if the alternator output was the same as
that of the battery.
If the reading on the volt meter is less than 12 volts
then you may have a failed alternator.
One last alternator check.
Turn on all the electrical items. Now have someone rev
up the engine again and check the voltmeter. It should
still be reading around 14 volts. If it reads lower than
13 volts the chances are that the alternator is faulty
and will need to be replaced before it fails completely. |
