Alternator Problems
Afaulty alternatormay cause one or more problems in the charging system of your car: The battery suddenly dies; the engine cranks slowly or fails to crank; the system overcharges the battery, or the electrolyte inside the battery frequently drops below its normal level. Whatever the symptoms, you need to make sure it is your alternator the root cause of the problem. You can do this by performing a few simple tests at home using a digital Multimeter and other common tools.Performing a base voltage testThis test will help you measure your charging system'sbase voltage. Turn the dial of your digital voltmeter to the appropriate setting, sot that you can read above 13 volts on the direct current (DC) voltage scale. Then, connect your meter probes to the battery terminals following the correct polarity (negative to negative and positive to positive). You should get a base voltage reading of 12.5 volts, approximately. If your reading is lower than 12 volts, you may have a discharged or damaged battery.Performing a no-load voltage testBasically, this test measures your alternator's output voltage without pulling current through the system. Turn off all electrical accessories in your car. Start the engine and ask an assistant to hold the engine speed at 1500 RPM. Connect your voltmeter to the battery terminals as you did in the previous test. This time, you should get a reading of 0.5 to 2 volts higher than your base voltage. A voltage higher than this might point to problems with your voltage regulator or circuit wiring.Load voltage testThe load voltage test is similar to the no-load test. This time though, you are going to pull current through the system. Start the engine and ask your assistant to hold the engine speed at 2000 RPM and to turn on all electrical accessories, including headlights, air conditioner, radio and blower motor. Now, go ahead and take a voltage reading as you did in the previous tests. This time, your reading should be 0.5 volts higher than your base voltage. If you obtained a lower reading, bypass the voltage regulator to locate the fault.Bypassing the voltage regulatorCheck the rear of your alternator and look for a small opening labeled Test Tab or a couple of terminals labeled BAT (battery) and FLD (field). If your alternator comes with a Test Tab, stick a screwdriver through the opening and let the screwdriver shaft touch the edge of the opening and the internal tab. Otherwise, you can short out the BAT and FLD terminals using a short jumper wire. Perform a load voltage test following the procedure described in the previous paragraph. If your voltage increases 0.5 volts from base voltage this time, you have a bad voltage regulator. If the voltage remains low, the brushes, bearings or some other part inside the alternator may be worn out. Repair or replace the alternator.If your test results turned out negative-no problems with the voltage regulator or alternator-check other common problems in thecharging systemthat might be affecting alternator performance. For example, you can inspect circuit wires for shorts or loose connections; check the battery terminals for corrosion or a loose drive belt. These tests only take a few minutes and can help you save time and money when facing a potential faulty alternator.
