How to Determine if the Alternator is Damaged?
3 Answers
Here are the methods to determine if the alternator is damaged: 1. Keep the alternator running and use a voltmeter to test the battery. The voltage reading at this time should be around 13 volts or slightly higher. If the voltage fluctuates between 13 and 14 volts at different speeds, the alternator is in good condition. On the other hand, if the voltage remains unchanged or decreases, the alternator is indeed faulty. 2. Start the engine, turn it off after a few minutes, and touch the alternator. If the alternator is very hot, the bearings may be worn or the insulated copper windings may be damaged, indicating that the alternator will soon fail. 3. Turn on the radio and start the engine. If the radio crackles or the sound quality becomes fuzzy whenever you step on the throttle, it is very likely that the alternator is problematic. 4. Measure and record the battery voltage with a voltmeter when the car is not running. Then start the car and measure the battery voltage again, recording the reading. If the car's alternator is not damaged, the battery voltage will be higher when the car is running. 5. Turn on the car's headlights and observe their brightness. Then start the car, and the lights may dim. If there is a noticeable change in brightness before and after starting, becoming much brighter, the alternator is normal, but the battery may be faulty.
Last time I was driving, I suddenly noticed the battery warning light on the dashboard came on, the AC airflow became weaker, and even the power windows were moving sluggishly. After parking, I measured the battery voltage with a multimeter—it was only 12V at idle (normally it should be around 14V), and revving the engine to 2000 RPM didn’t change anything. Later, when I popped the hood, I noticed a burnt smell near the alternator pulley, and the bearing was making a squeaky noise. The most obvious sign was when driving at night—the headlights would flicker, and my phone charger screen would also flicker when plugged in. My advice is to first turn off power-hungry devices like the stereo and AC. If the symptoms persist, it’s likely the alternator has failed. Get it fixed ASAP, otherwise, you risk getting stranded on the road.
My old car kept losing battery power, and the new battery I replaced only lasted three days before failing to start again. The mechanic taught me to lightly tap the alternator casing with a metal wrench—if it gets magnetically attracted, it means the field coil is still working. But mine showed no reaction at all. Later, we tested the static voltage: when the engine was cold, the battery showed a normal 12.8V, but after starting, it dropped to 11V (normally it should rise). When I pressed the accelerator, the voltmeter needle shook like an earthquake. Finally, we found that the alternator's rectifier bridge was short-circuited—it couldn’t charge the battery and was secretly draining it. Don’t delay fixing such issues; I’ve seen cases where the alternator completely failed, causing even the power steering to stop working.
