Alternator Battery Starter ¦ Understanding and Testing

For some reason most people immediately want to start replacing these components when the vehicle fails to start or the battery light comes on, etc. They never seem to consider that testing is an option. Perhaps that is because they do not know how to test. I hope to share enough information in this introductory article to slow this unnecessary parts replacement down.

Let's consider these components as a simple loop which should make it a little easier to understand.

The battery is used to store electricity and deliver it as needed. Many people including mechanics believe that the battery's sole purpose is to supply electricity to the starter to crank the engine. Over 25 years ago that was true, but not true in a very long time. The battery is an integral part of the overall 'on demand' electrical supply plus it acts like a filter for electricity by removing spikes that could harm many of the vehicle computers. It generates this electricity from an internal chemical reaction.

The starter is simply an electric motor that is used to crank the engine. The size, weight and electrical consumption of these motors have been reduced significantly over the years through the integration of permanent magnets.

The alternator is an alternating current (AC) generator that supplies direct current (DC) electricity through the use of an internal rectifier bridge. It supplies most of the electricity required to operate the vehicle except in extremely high demand situations and it also charges the battery during normal and low demand times.

To test these components requires common sense, knowledge and very few tools. The tools required ( a fuse tester, a 12Vdc light type circuit tester, and a digital multimeter (DMM)) are not very expensive and even most enthusiasts would have these tools.

You can get a Digital Multi Meter (DMM) HERE and a 12Vdc light type circuit tester HERE.

IF a vehicle does not crank (that is the action before the engine runs) then there are a few simple tests.

1st.. Do the circuit test lamps (idiot lights) on the dash illuminate at their normal brightness? (a) If no, then the battery may simply be discharged or bad. Try to jump start the vehicle. (b) If yes. Next step.

2nd .. When the key is turned to crank do they dim only slightly? (a) If no, goes almost dark. The battery may be low on charge (charge it) or the starter is bad. (b) If yes, the vehicles antitheft may be engaged preventing function (antitheft light flashing = engaged on most vehicles). Next Step

3rd..Turn the headlamps on and have someone watch their intensity as you try to start the vehicle. Did they dim drastically? (a) If no, there is a starter circuit problem. (b) If yes, the battery may be low on charge or the starter is bad. Try a jump start. Just remember to connect the cables properly. Positive to Positive and Negative to Negative.

IF the vehicle is running but the alternator or battery circuit test lamp on the dash is illuminated here is the testing;

1st..Turn the ignition off, raise the hood and check if the accessory belt is still attached. (a) If no, replace the belt (b) If yes, Next Step

2nd ..Using the 12Vdc circuit probe, carefully test for battery power at the back side of the alternator at the terminal which has the largest wire connected to it. Does it have power? (a) If no, check all the main fuses in the power distribution center. (b) If yes. Next Step.

3rd..Either remove the multi wire connector (usually 2 to 4 wires) on the alternator or find a way to probe the wires for voltage. Is there 12Vdc on one of the wires? If no. check all the fuses. (b) If
yes next step.

4th ..Turn the ignition key on, but leave the engine off. Using the DMM probe the other wires in the multi wire connector. Is there 12Vdc on one of the other wires. (a) If no check the fuses. (b) If yes, the alternator may be bad.

Testing the battery there is only one acceptable method and that is with a battery tester, either a tester like the Midtronics XL500 or a carbon pile load tester like a Sun VAT 40 (some frown on this tester as it being inferior, but use what your shop has available).

Today we place heavy demands on batteries and even the best ones have problems lasting much over 18 months to 3 years. Many believe this is because of 'Winter Cold' but 'Summer Heat is far more destructive, so keep this 18 months to 3 years figure in mind when recommending a battery. A battery with a 3 year free replacement is an excellent investment for the consumer, a shorter free replacement period is a gamble.

One very good tell tale sign that a battery has almost reached the end of its life is it starts corroding the cables badly, however Interstate batteries seem to do this almost immediately.

typical 3 wire alternator charging system circuit

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All above information is based on published information as of 01/2015 or products purchsed to confirm
 

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