“With the car running, you can turn on all the heavy loads; turn on the heater blower motor, turn the lights on, etc.,” he tells us. “Then check the voltage at the battery terminals. That'll give you a general idea of the health of the alternator.”
Start the engine and turn on dipped beam headlights to run the test. As in the multimeter method, you must first remove the minus terminal from the battery. The alternator works fine if the headlights give a steady light and the engine beat does not go off.
A battery test is easy to perform and can be done at home. First, open the hood and start the car. While the engine is running, remove the negative cable from the battery. If the vehicle stalls or dies, the alternator is likely bad.
01 Test voltage across the battery terminals with the engine running. A good alternator should maintain battery voltage between 13.9 and 14.8 volts (14.2 is optimum). Even worst-case, with all accessories turned on, there should be at least 13 volts at the battery.
Ripple voltage or (AC voltage) can be measured by switching your digital multimeter to AC and connecting the black lead to a good ground and the red lead to the “BAT” terminal on the back of the alternator, (not at the battery). A good alternator should measure less than . 5 V AC with the engine running.
To test a car battery, you'll want to set your multimeter to DC or DCV for Direct Current Voltage. If there's a voltage range, set it to 20 volts.
In general, stick to DC circuits (the settings on the multimeter with straight lines, not curvy lines). Most multimeters can measure AC (alternating current) systems, but AC circuits can be dangerous. A wall outlet with AC or 'main voltage' is the stuff that can zap you pretty good.
A good alternator should produce about 13.5 to 14.5 volts with the engine idling. If the voltage reading is low (12.5 volts or less), it indicates a charging problem but does not tell you what's causing it.
If you hear a whine or the sound goes fuzzy when you hit the gas, your alternator is probably failing. If the vehicle won't crank or start but the headlights are still working, look to problems with the starter or other parts of the engine.
Most alternators will last between 80,000 and 150,000 miles — or about seven years. However, your driving habits and the area where you live could wear it out prematurely.
Mechanics uses a computerized charging system tester to check your alternator. This is called an AVR test, and it can show if there's a weakness in the charging system, or if you'll need to repair or replace your alternator.
The alternator belt is the connection that interfaces the crankshaft and alternator together. If your car's alternator belt isn't working properly, your car battery won't get the charge it needs for your vehicle's electrical parts. With that, your car battery light will frequently be on to indicate such an issue.
Your car's battery holds a charge, but the alternator works to recharge it while the vehicle is on. That's why you can drive all day long without a problem but leaving the lights on overnight will drain the battery. If the alternator begins to fail, the battery will no longer recharge while the engine is running.
Set your multimeter to DCV (DC Volts) above 15. Make sure your alternator's positive and negative terminals are clean. Put the multimeter's black cable to the negative terminal and the red cable to the positive terminal. Look for an ideal alternator reading of around 12.6.
A corroded or defective alternator diode will faultily continue charging the circuit even when the car off. This, in turn, will drain your car battery and cause the car not to start.
Alternators can go bad suddenly, or slowly over time. If your alternator is slowly going bad over time there are some warning signs you can look out for.
The answer is simple - Yes, You can jump-start a car with a bad alternator.
When we take a closer look, we see car battery voltage can range anywhere from 12.6 to 14.4. With the engine off, the fully charged car battery voltage will measure 12.6 volts. This is known as “resting voltage.” When the engine is running, battery voltage will typically rise to 13.5 to 14.5 volts.
Read the voltage on the meter - Start the engine and observe the voltage on the meter. The voltage should read a minimum of 13 volts. A good alternator should put out between **13.5-14.5 volts. Stress test the alternator - Place a load on the alternator by turning on the headlights, the radio and the air conditioning.