How can you check an alternator? Alternator test with a voltmeter If it's in the range, it's good. Connect the meter leads to the battery terminals and look for That means the alternator is pumping out the juice.
Will revving engine charge battery? The battery will charge faster if you rev the engine faster. Because the faster the crankshaft turns, the faster it turns the belt that runs the alternator.
And the faster the alternator turns, the more electricity it produces to run all the electrical stuff in the car — and recharge the battery. How do I know if it's the alternator or the battery? A simple test to check the working of the alternator is by running your car; and then unplugging the positive connection of the battery.
If the car stops, then you most likely have a problem with the alternator. Another simple test is to check your interior lights. How do you check alternator amps?
Turn on all the electrical equipment in the car: lights, stereo, wipers and everything else you can. Current output increases with engine speed, from around 20 to 50 amps at idle up to the unit's maximum output at 2, RPM or higher refer to a service manual for the exact charging output specifications for your vehicle. It can also be measured on an alternator bench tester in a auto parts store. Alternator power ratings can also be given in Watts which is volts times amps.
Many alternators in foreign vehicles are rated in watts rather than amps. The important point here is to make sure a replacement alternator has the same power rating in amps or watts as the original so the charging system can maintain the same power output as before, should the alternator need to be replaced. In fact, on some applications upgrading to a higher output replacement alternator may be recommended if the vehicle has a history of alternator failures, or the vehicle has a megawatt aftermarket sound system, emergency or off-road lighting, or other power-hungry electrical accessories.
If the alternator is working hard under a heavy load at low RPM especially during hot weather , there may not be enough cooling to prevent the unit from overheating.
This tends to be more of a problem on vehicles where the location of the alternator restricts airflow and cooling.
The alternator may be forced to work harder than normal if the battery cables, ground straps or other electrical connections in the charging circuit are dirty or loose. A poor connection increases resistance and causes a voltage drop across the connection. This, in turn, reduces the flow of current through the charging circuit. The electrical system is, after all, just a big series of loops that carry current from the charging system to the battery, and from the battery to all of the vehicle's electrical accessories and electronics.
The return path is usually the vehicle body, which serves as the main ground circuit for almost everything. All the power supply and ground connections must therefore be in excellent condition to minimize resistance and the load on the charging system.
In fact, poor ground connections are an often overlooked cause of low charging output and alternator failure.
One of the most common causes of charging problems is the failure of one or more diodes in the alternator. Alternators have six diodes three negative and three positive that convert the alternating current AC to direct current DC.
They are called a diode trio because each negative diode is paired with a positive diode. A little current also flows through the charging light indicator circuit. On GM alternators, the indicator light circuit is terminal 1. On Asian alternators, it is usually labeled L. This terminal leads to the ground side of the alternator warning light.
When the alternator is charging, the diode trio supplies voltage to the ground side of the indicator light. This offsets the battery voltage applied to the positive side of the light, causing the light to go out once the engine starts.
If the alternator stops charging, current flows though the light circuit from the positive side causing the charging system warning light to come on.
If one of the diodes fails, it may cause the charging system indicator light to glow dimly. If two or more diodes fail, the light will get brighter. At the same time, the feedback current from the diode trio will reduce the alternators ability to produce current. So the more diodes that fail, the less power the alternator will generate. A bad connection or open circuit between the alternator output terminal and the positive battery terminal will force the charging current to follow a parallel route through the diode trio and out of the alternator.
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! 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. Different radios and different computers might have different standby drains, as might accessories like clocks, but in no case should "overnight off" leakage exceed 25 mA or so.
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.
The meter above is on the 20 mA scale, and is reading 1. That is nothing. The battery charge would probably last for months of sitting. If the test light lit, you will want to locate the wire loading the battery. First make sure all lights are off. You can do this by having someone open and shut things with lights, like the trunk, and watching for a define large load change.
You should see a definite load change when shutting doors with lights, like the glove compartment. Connect the test light in series with the negative post, and start pulling feed wires. The first to check is the heavy charging wire from the alternator. A bad or leaky diode in an alternator is a very common source of overnight battery drain.
Connect wires one at a time to see what lead is drawing current. Click here to view past issues. For some, a constant Click Here to Read More Advertisement O ne test is not enough if you are diagnosing a charging system problem.
All too often, the alternator is condemned as the source of the problem if only battery voltage is present with the engine running. If this is the case, it only means that the alternator is not charging, but does not reveal why. Advertisement This wide discrepancy in voltages is due to the fact most alternators are controlled by the ECM or PCM to improve fuel economy.
This means that load on the engine is controlled to reduce parasitic loss at the crankshaft. Alternator output is on demand when there are loads detected or the battery needs to be charged.
Depending on ambient temperature, charging voltage varies. The actual charging voltage designed into a voltage regulator is dependent upon factors such as how far the alternator is located from the battery and the ambient air temperature surrounding the battery as calculated by the PCM. This is why the ambient and underhood temperatures are critical data for the charging system.
Advertisement Another factor determining battery voltages are automatic transmissions with five or six speeds that can drastically reduce engine speed when cruising. Many modern engines operate well under 2, rpm until they reach highway speeds of about 60 to 70 mph.
In most cases of undercharging, the alternator may have an incorrect diameter pulley installed, the drive belt may be slipping or the alternator itself might be under capacity for the vehicle application. Although load-testing an alternator provides a quick way to test for drive belt slippage, keep in mind that an alternator can easily be overheated when testing for maximum output during low-speed operation for an extended period.
Most alternators wi. Some systems might even stop charging if an extreme load is detected and set a code. Advertisement Not knowing what controls what, and how it is supposed to function, can cause a misdiagnosis.
This might also cause you to overlook critical problems. Take time to look at the service information. The other critical tool to effectively diagnose an alternator is a scan tool. On older vehicles, the battery light would turn on the alternator light when the alternator output or battery voltage dropped below a preset value.
0コメント