How to test an alternator

If your car won’t start, it might not be your battery. Believe it or not, your car’s lights, dashboard instruments and even the radio are not solely powered by the car battery. It’s actually the alternator that’s putting in the work to keep things running.

While your battery is responsible for starting the car, your alternator is what keeps your car alive and the engine on. Even the luxuries of electric steering, air conditioning, power windows and heated seats are all thanks to the alternator.

Testing alternator parts is a good idea to prevent issues like malfunctioning car electronics, troubles starting the car, frequent stalling, or even permanent engine damage.

Which alternator do I have?

Your car alternator can differ based on the current it generates. There are two basic types of alternators: fixed voltage and smart alternators.

Fixed voltage alternators provide a higher current after you start your car. When the car battery is back up to charge, it reduces the current whilst you’re driving.

Smart alternators have voltage regulators and electronics to help monitor and vary the charging current according to your car’s electrical needs. The smart alternator delivers a higher voltage and current right after you start your vehicle, and then it systematically reduces as you drive.

To identify which type of alternator you have, you can test your vehicle with a voltmeter attached. Take it for a drive with a helpful passenger, and during the drive ask your passenger to monitor the meter. If the voltage goes up and down between 12-15V, then the vehicle has a smart alternator. If it stays steady and consistent at about 14V, then you have a fixed voltage alternator.

Signs your alternator may be on the way out

Your alternator will show signs that it is faulty or not working properly. Most commonly, you’ll see:

These are all signs it’s time to check your alternator, or bring your car to a local mycar mechanic for a checkup.

How to check if the alternator is working properly

If your car is overdue for a service, it’s a good idea to test your alternator to prevent future problems. Knowing how to check the alternator by yourself isn’t too complex. The easiest method is the battery test.

How to test an alternator with a multimeter

Normally your vehicle should be checked by a mechanic, but if you have a multimeter, you can perform a DIY test yourself. A multimeter is a tool used by mechanics to measure two or more electrical values, such as voltage.

To test your alternator with a multimeter:

1. Set the meter to ‘Volts’

2. Locate the battery in your vehicle

3. Make sure the engine is off

4. Get a base reading of the battery voltage by taking your multimeter’s black and red probes and placing them on the vehicle’s battery terminals

5. The battery voltage reading displayed on the multimeter should be around 12 Volts - a sign of a good battery

6. Now it’s time to start the car

7. With the vehicle running, place the multimeter’s probes on the battery terminals

8. Check the multimeter screen display for the alternator reading

A good alternator will be putting out around the 13.9 - 14.3 Volts. If the reading is below this mark, it could be a sign that your alternator is on its way out. If the voltage is similar to your base reading (when the vehicle is turned off), then the alternator is not working and requires replacement.

If your vehicle is not starting properly, and you’re overwhelmed with the process of testing the alternator, speak to the professionals at mycar. With multiple stores across Australia, our friendly team will help with your vehicle inspection and ensure your car is functioning at its best.