Good quality alternators can have a long service life, and even last the life of the vehicle.
Sometimes, though, you may have a case of either premature failure or worse still repeated alternator failures.
So in this post, I will cover the common causes of alternator failures, why your alternator replacements may keep burning out, signs that an alternator is about to fail, tests you can do for an alternator, and provide tips as well to get your alternator to last as long as possible.
What Causes Alternators to Fail Repeatedly?
One common cause of repeated alternator failure is when the alternator is forced to work at maximum output for a long time, overheating in the process and damaging the internal windings.
This can happen in a number of ways including when the alternator charges a deeply discharged battery, a damaged battery that demands an unusually high current output from the alternator.
What Can Damage an Alternator?
In addition to overheating, an alternator can also be damaged:
# 1. Disconnecting the alternator output (B+) terminal from the battery positive terminal when the engine is running.
This can result in overheating of the alternator when high current draws flow through the diodes through alternative routes to the battery.
# 2. Connecting it to a damaged battery with an internal short for instance can force a high current draw from the alternator leading to overheating and potentially premature failure.
# 3. Reversing the polarity of the alternator connections – connecting the alternator B+ terminal to the battery negative terminal and the alternator ground to the battery positive is bad for the diodes and can damage the alternator.
# 4. Exposing the alternator to excess water for a long time. The water affects the lubrication in the alternator bearings and the smooth running of the alternator and its ability to reliably meet the power demands of the vehicle.
You may want to read: Car alternator bearings: 6 Things you should know
# 5. Loose or weak wire connections between the alternator and the battery. The bad wire connections restrict the flow of current, slowing down the charging of the battery.
This in turn causes the alternator to run for a longer period and a higher rate that can lead to early failure.
# 6. Normal wear and tear can also kill the alternator. Car alternators operate in demanding environments that subject them to heat and stress on the insulation from meeting the electrical demands of the vehicle.
You may want to read: 7 Common causes of overheating in car alternators
Over time, this can cause the alternators to fail on their own with no fault on the rest of the components in the charging circuit – battery, wiring, and others.
# 7. Accidentally shorting the alternator positive terminal (B+) to the ground while the car engine is running.
The large currents drawn put enormous stress on the alternator’s electrical components over what it is designed for damaging it in the process.
Signs that Car Alternator Is Failing
While these signs are not confirmation of a failed or failing alternator, they can point to a bad alternator or one that is about to fail.
Abnormal noise coming from the alternator. This could be a case of worn-out alternator bearings and or a misaligned drive belt.
Flat battery on some days and other days the charge is good. You could have an alternator problem if the car battery is not being charged consistently
The car engine suddenly dies as you are driving. If the alternator is not able to supply the required power to keep your car running, could be a case of excessive electric loads on the alternator or a failing alternator and the car runs out of battery power, then the engine will die.
Extremely hot batteries, bulging batteries. Extremely hot batteries might be a case of overcharging by the alternator.
This can be a case of a malfunctioning voltage regulator on the alternator.
Battery light comes on while driving yet you have a new good quality battery.
If the battery light comes on while driving and yet you have a new good quality battery, then you might have a case of a failing alternator. Note, it can also be a case of loose or weak battery connections.
Signs of a dead car alternator
Your car alternator is probably dead and needs to be replaced if:
You measure the output voltage across the battery terminals while the engine is running and the voltage is less than 13.5V.
You fully charge a previously drained but good quality battery, confirm that the battery connections make firm clean contact, there are no parasitic loads draining the battery and the car engine dies on you while driving or the battery voltage is not enough to start the car after parking for several hours.
How to Test an Alternator?
You can perform a quick test to check the performance of the alternator by measuring its output voltage while connected to the battery with the engine running.
You can read this post on Bad car alternator vs bad battery for expected voltages from a good alternator.
A more accurate test involves checking the alternator’s regulated voltage and current output on load.
This is extremely useful in the case of an alternator that is degraded and no longer providing the expected power output. Such cases can be difficult to troubleshoot.
This test can be done at an auto workshop.
Alternator regulated voltage test
In this case, the alternator is run at about 2,000 rpm, and the output voltage is measured when the current draw on the alternator is about 10A.
This is then compared against the standard values for the vehicle manufacturer.
Alternator regulated current test
In this case, the alternator is run at about 2,000 rpm and loaded by switching on high beam lights, blower, and other loads to read the output current on load.
This is then compared against the standard values for the vehicle manufacturer.
Tips to Prevent Your Alternator from Failing
Some causes of alternators are avoidable. Here are some tips to keep your alternator working as long as possible.
- Do not disconnect the alternator from the battery while the engine is running
- Avoid exposing the car alternator to water. Excess water affects the alternator bearing lubrication and can lead to early failure.
- Do not short-circuit the alternator positive output terminal (B+) to the ground.
- Avoid reversing the alternator’s positive and negative terminal connections to the battery.
Final Thoughts
Overheating is a common cause of failure with alternators.
Running alternators at maximum output for a long time leads to overheating.
Alternators may be forced to run at their maximum output in the case of loose battery cables, connecting them to deeply discharged or faulty batteries, or disconnecting the battery terminals when the engine is running.
You may be able to tell that the alternator is about to fail if the output voltage is less than 13.5VDC with the engine running.
A more accurate test is to conduct both regulated voltage and current output tests with the alternator on load.
