Is My Alternator Faulty?

Is My Alternator Faulty?

Tuesday, January 16th, 2018

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Posted by: Harriet Johnson

What Is An Alternator?

Alternators are commonly used in ‘newer’ vehicles. Their function is to charge the battery and get power to the electrical system when your engine is turned on.
The alternator earns its name from the term ‘alternating current’ or AC.
Nearly all alternators are seated using brackets which bolt on to a specific point on the engine.

Is My Alternator Faulty?

You may be experiencing slow start ups, flickering headlights or a warning light on your instrument panel, but is it the alternator?

Milner’s have put together a quick test to help you out.

The Multimeter test.

For this test you will need a multi-meter / multi-tester / voltmeter. These can be purchased online or at your local motor factors, you may even have change left from a tenner.
With the engine switched off, connect the meter to the battery terminals RED positive & BLACK negative. (Do not connect these to the cable clamps)

The meter should read a minimum of 12.3 volts or if you have a good condition battery, it should read at least 12.6 volts.
If your meter is showing below this reading it could be a result of one of the following reasons:

  • The battery is discharged. (Recharge your battery)
  • The battery is low on distilled water. (The water should be 5mm above the plates. DO NOT fill the battery full to the top).
  • The battery has a high internal resistance. (Sulphide plates)

Multi-meter test

IF your battery is in good condition.

Start your engine and rev to 2000 RPM. This will draw power on the battery and cause the voltage regulator to start the alternator working. Let the engine idle and the reading should be:

  • A minimum of 13 volts.
  • Revving the engine will fluctuate the voltage between 13 to 14.5 volts, which indicates the alternator is in good shape.
  • If the voltage when revving the engine stays the same or decreases, then your alternator is more than likely faulty.
  • To test the regulator, repeat the process with the lights, radio and A/C (if fitted) switched ON.
    Rev the engine again to a constant 2000 RPM. The meter reading should read above 13 volts and no more than 14.8 volts. IF the meter reads above 14.8 volts, the alternator is probably over-charging.

If you are unsure on the above, take your vehicle to your local garage and get them to do the test for you.

 

(The above information is a guide only. It is down to the operator to gain the correct voltage tolerances for the vehicle on test. The above tests are for a standard 12 volt negative earth system. A good working battery will show 12.6 volts and a minimum of 12.3 volts.)

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