Car struggling to start? Before you blame the battery, you should consider that a faulty alternator could be to blame. If you’ve never heard of the word alternator it’s ok – this rarely mentioned part not only provides power for everything from the battery to the spark plugs, it is responsible for keeping your entire cars electrical system running smoothly. They rarely require replacing but when they do, you should know the signs and, more importantly, how much an alternator replacement will cost.
Often the first sign we get that something is wrong with the alternator is a car that refuses to start because of a flat battery. Starting an engine puts a significant load on the battery and it takes time to recharge. If the alternator isn’t providing enough voltage to recharge the battery, it will quickly go flat.
As alternators are belt-driven, a worn or snapped belt will cause it to stop working. When this happens problems with the car’s electrical system will be present with another sign such as loss of power steering or engine overheating as the belt that drives the alternator is usually the same belt driving the power steering system and radiator fan.
Other common signs of a bad alternator are the low battery warning light on the dashboard becoming illuminated, as well as dimmed or pulsing interior and exterior lights. The alternator is responsible for powering these and any signs of flickering lights are a sure sign that something is wrong with the vehicle’s electrical system.
Your mechanic will use a multimeter to determine if your alternator needs to be replaced. But this is an easy process and you don’t need to be a mechanic to test your alternator using this method, so we’ll run you through how to test an alternator using a multimeter.
If the car is running, switch it off. For an accurate reading, the car should not have been driven recently and testing first thing in the morning will give you the best results. Make sure the battery terminals are clean and clean with a wire brush if needed. Switch the multimeter to the 20 DC volts (DCV) setting. Attach or contact the black probe of the multimeter to the negative battery terminal and the red probe to the positive terminal. This will give you a resting voltage for your car battery which should be around 12.6V. A lower reading than this can indicate something is draining the battery.
How to test the alternator is simple, as the same test is carried out on the battery but with the engine running. Be wary of, and keep clothing and fingers clear of moving parts when performing this test. The normal output for the alternator is between 13.8 and 14.4 volts. Any reading over or under this range indicates the alternator is overcharging or undercharging the battery and when considered in conjunction with the other signs of a bad alternator, point to a faulty alternator.
Despite their frequent use, alternators are usually relatively trouble-free, and when a problem occurs, it’s recommended to replace the alternator rather than repair it. The logic behind this is because a repair or rebuild can cost almost as much as a replacement alternator. The other consideration is because a new alternator will last longer than a refurbished one, and it usually comes with a warranty.
That said, there are some circumstances where repairing an alternator may make sense. If the belt is showing signs of wear or breaks, an alternator belt (sometimes called a serpentine belt) can be sourced and replaced without having to replace the alternator itself.
Some alternator parts can be easily replaced such as bearings. These can fail due to inadequate lubrication or excessive wear. Wiring connections can become loose or even break, disrupting electrical output. In some cases, these may be able to be soldered back together and repaired. The diodes on the rear of the alternator can become damaged by excessive heat, causing a break in current output. They can even leak which causes the battery to drain.
Repairing an alternator is a job for an auto electrician as it requires a particular set of skills. Another option, if replacing your alternator is too costly, is to fit a refurbished or rebuilt one. Not all the internal parts will be new, but any parts that needed replacement will have been discarded and fitted with new ones. We generally don’t recommend this option as it’s impossible to know the quality of the workmanship but it is an option for those on a tight budget.