How to check car alternator

Symptoms of a bad voltage regulator may include: High voltage output Low voltage output, sometimes No voltage output Lights dim or flicker Faulty high-beam headlamp bulbs Engine working erratically weak or flickering ignition system Adding water to the battery frequently Growing corrosion around battery terminals and top Dead battery Battery or check engine light indicator lit on dashboard Some of these symptoms may come from loose or corroded charging system connections. What Does a Voltage Regulator Do? Check Your Alternator Parameters Always check the charging system specifications for your particular vehicle model to correctly interpret your system test results.

Voltage Regulator Test This test is a simple procedure to check alternator voltage regulator output.

What is an alternator?

Set the parking brake and shift the transmission to Neutral manual or Park automatic. Set your multimeter to DC Voltage and select the 20 Volts in the scale. Notice the open-circuit voltage of the battery. Your battery should be at about Now, ask an assistant to start the engine and run it at rpm. Take a note of your voltmeter reading. If you noticed an output voltage reading below 13 volts right after starting the engine, there could be a charging system problem. If the output voltage reading is 16 volts or higher, there's an overcharging problem.

This usually indicates a bad voltage regulator.

How to Test an Alternator - Diagnose Charging Issues

If voltage seems to fluctuate during your test, switch your voltmeter to the AC voltage scale and take another output voltage reading with the engine still running. Usually, the presence of 0. But some manufacturers recommend replacing the alternator if 0. However, if you have noticed engine performance issues, this might be the problem. Consult your vehicle repair manual for acceptable diode leak rate, if necessary. If your output voltage is within specifications, continue with this test: With the engine running, increase engine speed to rpm.

Turn on the headlights, AC, defogger, and other high current accessories you may have. Checking Wires Using Voltage Drop A quick way to examine the wires and connections in the charging system is to check for voltage drops. Set your voltmeter to 2 volts.

How to Tell if You Have a Faulty Alternator

Start the engine and let it idle. Measure for voltage across individual wires and connections in the charging system. If there's voltage over 0. When fixing wires and connections, aim for a voltage drop of less than 0. Voltage Regulator Bypass Test On many alternators except those with computer voltage regulation , you can bypass the voltage regulator to test whether your voltage regulator or some other component alternator or charging circuit is at fault.

If the rear of your alternator has a 'test tab', you need to short this tab to the alternator frame using a screwdriver while checking voltage output at the battery with the engine running. On other systems, you may need to connect the battery and field terminals using a jumper wire while checking voltage output at the battery with the engine running. Consult the vehicle repair manual for your particular model to conduct this test, if necessary.

When the voltage regulator is bypassed, you should see maximum voltage output. If voltage output is at a normal level, most likely the voltage regulator is faulty. If voltage output remains at the same level as in your initial test, most likely you have a faulty alternator. The next video shows you how to test an external voltage regulator and how to bypass it. Voltage Regulator Adjustment Some alternators with an old configuration allow adjusting of the voltage regulator. Connect your voltmeter across the battery posts. Set the Parking brake. Shift the transmission to Neutral manual or to Park automatic.

Turn off any accessories, if necessary.

Check battery charging voltage. Turn the adjusting screw using a small screwdriver to adjust charging voltage to specifications. Testing a Contact-point Voltage Regulator Old type DC generators and early vehicle charging systems used a contact-point type voltage regulator. Still, there might be some vehicles on the road today fitted with this type of regulator. To repair a contact-point voltage regulator: File, test and adjust the regulator points, as necessary.

If still, voltage output is out of specifications, replace the regulator. Refer to the repair manual for your particular vehicle make and model. Voltage Regulator Replacement To replace it, remove the voltage regulator from the back or inside the alternator. Your warning light is on. Many modern cars make it easy for you spot an alternator issue because they have a dashboard warning light.

Recent Blog Posts

The warning light in a majority of vehicles will take the shape of a battery, however, some differentiate the route of the problem by displaying ALT for alternator or GEN for the generator. You spot visual clues One obvious sign of a bad alternator is any noticeable damage to the serpentine belt, or, one of the connecting belts. Does it look loose? Or maybe too tight? You might even notice that a belt is looking worn or cracked. Your car battery is flat. While a car battery can fail of its own accord, it can also be caused by the alternator not functioning correctly.

How to Test an Alternator for Problems | AxleAddict

This is because the alternator is failing to recharge the battery, meaning it uses up its capacity. For more information about spotting the signs of a failing alternator, check out our previous guide by clicking here. If you spot the early warning signs of a failing alternator, you could avoid a costly breakdown. So, you suspect you may have a problem with your alternator but what do you do next? It is possible to run basic checks on your vehicle using a multimeter. A multimeter is a testing tool that measures two or more electrical values. It typically includes a voltmeter, for measuring volts, an ammeter for measuring amps and an ohmmeter for measuring ohms.

Step One: Set your Multimeter

Toggle navigation. David Taylor 28th Feb Your lights are dim Are your car headlights dim? The battery above will slightly gas, but not enough to be harmful, and the battery will get a quick full charge recovery after starting. Less than Much less than When running at a normal slow cruising engine RPM, the voltage across the battery terminals should stay over If this system was in a restored GT coupe, I would probably change the regulator to reduce maximum alternator voltage. This would prevent deterioration of metal around the battery from excessive charging vapors. It's OK in my daily driver as long as I watch the battery for purged acid deposits.

If you measure battery voltage and it is anywhere over If voltage is over Turn the motor off with no load headlights, etc. With the engine just shut off, the battery voltage should be The exact voltage varies with the battery, how quickly you read it, and the state of battery charge. This voltage is not too important because the battery will slowly and steadily settle to a new voltage that indicates the true state of battery charge, but the voltage measured right at engine shutoff is a very clear indicator if the alternator or charging system is charging. If the voltage is over To test the electrical system for unwanted loads draining power, shut everything in the car off.

Do just like you would do things when parking the car overnight. Remove the negative post wire and check current draw with all electrical loads off using a test light. I made a test light from an old tail lamp bulb. The dull glow in the light filament indicates a current drain problem. At this point I do not want to connect a current meter to check leakage because the short could damage the test meter!

How to Test an Alternator?

If a small clear test lamp like this does not light, then it is generally safe to directly measure current drain with a test meter. With all electrical loads off connect the meter, on a low amperes scale of about 1 ampere or so, in series with the battery negative post to ground.

The positive meter lead connects to the car chassis, and negative meter lead to the negative post of the battery. This is measured on the 20mA scale. The mA scale reads in thousandths of an ampere. My Mustang LX, after I changed a bad alternator diode, now has about 1. My Kenwood stereo draws 1. If you have a digital clock that stays on, an alarm, or some other load this current will be higher.

At 75 mA, leakage could compromise battery life of infrequently driven vehicles.