Turn the lights, radio, fog lights, fan, and other electronics on, making sure the voltage reading doesn't go below 13. When you shut off the car, make sure the reading is above 12.6. If any of these readings are off, you likely have an issue with your alternator and may want to visit an auto repair shop.
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.
Checking the alternator directly
Locate the alternator within the vehicle and ensure its belt isn't loose. Rotate the multimeter dial and set the knob to measure DC voltage in the range of 15-20V. Start the car engine. Check whether the alternator belt is spinning properly without slipping.
If your car starts but stalls when you're underway, your battery is probably not being recharged due to a faulty alternator. A squealing sound coming from the engine that gets louder when drains like the heater or sound system are on may be your alternator bearings.
Here's how to tell if your alternator is bad. One of the most obvious signs is if the car dies after a jump start. The alternator should provide enough current to keep the vehicle running even with a bad battery. If it doesn't, then your alternator needs to be examined.
If the engine starts but dies immediately, your alternator probably isn't keeping your battery charged. If a jump starts and keeps your car running, but the car can't start again off of its own power, a dead battery is probably your answer.
The answer is simple - Yes, You can jump-start a car with a bad alternator. But, can You drive such a car, and for how long, that is another question.
How mechanics test the alternator. 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.
A parasitic drain is frustrating to deal with since it can be intermittent and often leaves you with a dead battery when you least expect it. In some cases, it can be severe enough to deplete your fully charged battery overnight.
You can check the alternator by simply starting your car and then disconnecting the negative battery cable. Be careful doing this, though, because there are a lot of moving parts in your engine compartment that could cause injury.
You'll disconnect the negative battery terminal to test the alternator. If you disconnect the positive battery terminal it could cause serious damage to your car's computer system.
Some people believe that you can just tap the alternator with a hammer to get it to operate. You should not do this because it will damage the part and you might even damage the surrounding parts to the car, resulting is a large car repair bill.
That said, an alternator can take time to fail or can stop working suddenly. Usually, people recognize the whining sound that comes from a bad alternator and get it fixed before it breaks down completely.
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.
The simple answer to this question is yes, your car's battery will start to charge as long as your engine is running. As long as the electrical systems aren't draining the battery quicker than the alternator is charging it, it is technically possible to completely charge your battery using this method.
An effective method to determine whether it's your battery or alternator that's gone bad is to connect jumper cables from a running vehicle's battery to yours. After a few moments, try starting your vehicle. Once it's started, remove the jumper cables — if your engine stalls, your alternator has probably gone bad.
If your alternator is malfunctioning by over-charging your battery, disconnecting it may allow the alternator to provide an even higher voltage to the car electronics, and potentially damage those sensitive components.
Absolutely not! I cannot stress this enough. Disconnecting a battery cable while your car is running is a big no-no when it comes to testing your car's alternator. It might seem like a quick and easy way to check, but trust me, it can lead to all sorts of troubles.
If the engine's already running, disconnecting the battery will still keep the engine running. If you're trying to start a car without a battery or with a very dead battery, it won't start (even with push start in a manual car) because there's no electrical supply (spark) to the combustion chamber.
Does a Bad Battery Affect Your Starter or Alternator? A bad battery won't usually harm your starter or alternator, however, since both of those components get their voltage directly from the battery, if the battery is underperforming, both the alternator's and starter's performance will be affected as well.