Electrical PM

John Baxter | February 01, 2012

Attention to electrical system maintenance will prevent a no-start or sudden loss of power — and extend alternator life.

The alternator connects the engine and the electrical system. It converts rotating power from the crankshaft to 14-volt current to charge the batteries and operate all lighting, gauges, the engine ECM and the electronic portion of the injection system. The starter plays the reverse role, converting the battery’s stored electricity into cranking power.

Wiring like the large, red, positive connection to the starter on the back of this alternator is just as important as the alternator, starter and batteries. Connections must be clean and tight. Cables must have low resistance.

While the alternator is fairly trouble-free, its function and long life depend on battery maintenance and the maintenance of all the wiring and ground systems that ensure low-resistance electrical circuits. A certain electrical system symptom can signal a problem in one or more areas, so maintenance and troubleshooting should not be restricted to one or two components.

Battery maintenance

Alternator maintenance is more about maintaining the batteries than the alternator itself. A good alternator lasts almost forever, but only if it doesn’t overheat. One good way to prevent such overheating is to keep the batteries working efficiently.

Battery grime should be cleaned periodically. Corroded connectors need to be cleaned with an abrasive material or special battery post cleaning tool. Resistance in these connections will reduce cranking power as well as prevent the batteries from being quickly charged after a cold start.

The alternator’s main job is to handle the vehicle’s electrical load, calling on 75 percent or more of its output. New batteries and good wiring reduce battery charging needs, making life a breeze for the alternator. As batteries and cables develop resistance, the alternator works harder and longer to replace what’s used for starting or supplying overnight shutdown loads.

Testing batteries once a year, preferably just before the weather gets cold, is critical.

Testing reliable start power

1.  Disconnect the cables to isolate the batteries.

2.  Use a carbon pile load tester – a big electrical resistance – to put half the rated load on each.

3.  Check the output voltage for 20 seconds of continuous loading with a voltmeter. If the voltage stays at or above 9.5 volts for more than 20 seconds, the battery will get you started.

Use a special, circular wire brush to clean battery posts. Some can be chucked into a drill to speed the process and do a more thorough job.

Voltage on a battery that is close to failing will fall off by the end of 20 seconds. If any battery fails this test, replace the entire set to ensure long life. You can inexpensively have this test done at a dealer or repair shop if you can’t do it yourself.

While this test will help ensure reliable starts, it’s harder to determine whether batteries are gradually starting to tax the alternator by losing their reserve capacity, notes Bruce Purkey, president of Purkey’s Fleet Electric. He suggests two ways you can check on this:

Testing reserve capacity

1.  Establish a baseline for good batteries by testing them when new.

• Turn off the engine. Measure battery voltage.

A hydrometer can be used to measure charge by indicating the density of the electrolyte in the cells of conventional batteries. When fully charged, the colored balls float, as shown here.

• Turn on headlights and let them drain the batteries for 30 minutes. Retest the output voltage and record the reading.

• After a year or two, you can repeat the test. After 30 minutes, if voltage drops more than when new, it shows a reduction in reserve capacity.

2 Carefully monitor battery performance while shut down overnight if you have an inverter with a low-voltage cutoff. If your typical overnight load is fairly constant, note how long it takes to get a low-voltage warning or cutoff. When that interval becomes significantly shorter, it’s time to replace the batteries.

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