How to Check an Alternator

Have you ever wondered how a car manages to supply enough electric power to sustain the various electrical appliances including the headlights? Of course, it is because of the car battery that this is possible. However, it is because the battery charge is replenished regularly by the alternator!

An alternator is car's electrical generator, that enables it to generate its own power. When the battery goes dead, we mostly suspect that something is wrong with the battery, but more often the culprit is a problematic alternator.

To learn about alternator testing, it will be helpful if you have a rough idea about its internal working. That knowledge can help you understand what has gone wrong with the alternator.

The structure of an alternator assembly is the same as any dynamo or electrical generator. It consists of a stator, a rotor, a diode, and a voltage regulator. The stator is an arrangement of magnets, inside which the rotor rotates to generate electricity, through electromagnetic induction.

The diode converts generated AC voltage to DC voltage, which is used to charge the battery. The voltage regulator sees to it that the desired output voltage is maintained. It switches off charging when the battery is charged to full capacity.

The rotor is driven by the alternator belt, which in turn is driven by the torque derived from the crankshaft. Thus, engine power is utilized to generate electric power in a car.

The gist that must be taken from explanation is that the alternator charges the car battery. Hence, if anything is wrong with the car alternator, it will reflect on the car battery's output. So one can indirectly check if an alternator is working by checking out the car battery voltage output.

Let us see how to check the function of the alternator that is armed with a voltmeter. A standard DC voltmeter or a multimeter will be good enough for the job. There are three stages of checking the alternator voltage. First is checking the car battery voltage output. Shut down the car and open car hood to locate the battery.

Using a standard voltmeter or multimeter (with its knob turned on to DC Voltage), check the output of the car battery. Connect the positive (red) terminal of the voltmeter to the positive terminal of the battery and connect the negative (black) terminal to the negative of the battery.

If the voltage reading is around 12.6 V, then the battery is charged fully. If the voltage is substantially lower than 12.6 V, then there may be some problems with the alternator or the battery itself.

Next, you can move on to check the alternator itself. Locate and observe it for any external signs of malfunctioning. Check whether the alternator belt is taut enough and that all the wire connections are in place. See to it that the wire which connects the alternator output to the car battery is properly connected.

Now turn the car on and put the engine in neutral gear. Let it run for a while. Then, while the engine is idling, check the voltage output of the car battery.

Ideally, with the car engine running and the alternator supplying charge, battery voltage should be in the range of 13.6 V to 14.3 V. If the observed voltage output is below the expected voltage output, then there may be something wrong with the alternator and you need to get it checked as soon as possible.

It is important that you include a battery and alternator checkup in your car maintenance routine. That will prevent situations where the battery goes dead, due to alternator failure and one is left stranded on the road.