Alternators and batteries need regular care.
Do you take your rig’s electrical power for granted? Do you do all the regular maintenance and checks on mechanical parts but don’t do the same for the battery and alternator?
If you do, it’s possible that one day you will turn your ignition key and hear only silence.
The alternator converts the mechanical energy the engine makes out of diesel fuel into electricity to supply the entire system. The batteries are there to store the energy in order to start the engine after a shutdown. They also may stabilize the voltage and contribute to the energy supply for short periods when you are idling or running slow with a lot of lights and other accessories turned on.
Routine maintenance is key to keeping power flowing.
Routine checks on alternator output voltage and battery storage or output capacity are also recommended.
Routine maintenance of alternators
We visited Philadelphia Freightliner in Bristol, Pa., where the dealer’s service manager, Denis Granville, guided us through all needed routine alternator maintenance for a typical heavy truck.
We first took a look at a 2005 Freightliner Columbia’s alternator.
If a serpentine belt should need replacement, the first step is to note its routing, making a drawing if you think you might not remember it accurately. Then insert a 1/2-inch breaker bar’s square end into the square hole in the tensioner and rotate it in the direction of increasing spring tension. This will relieve belt tension, allowing you to remove it. To replace the belt, first work it around the crankshaft and alternator pulleys and those of any other accessories it drives. Then rotate the tensioner far enough in the direction of increasing tension to allow you to work the belt around its pulley. Finally, gradually release the tension with your breaker bar.
Routine battery maintenance
“You get big problems with batteries caused by vibration,” Granville says. When the batteries are tightly mounted to the battery box, they ride up and down gently with the truck suspension. But when their hold-downs get loose, they bounce around, and this often damages the relatively delicate plates and internal connectors. On the latest models, check the positioning of the three or four battery hold-downs and tighten, preferably with a torque wrench, once a year. On late-model Freightliners the torque is eight to 12 pounds-feet. Where torque is critical, such fasteners will normally be marked. On older trucks with side battery boxes, inspect the hold-down J-bolts and make sure they are properly inserted into the holes in the side of the battery box at the bottom. The hold-down on older Freightliners ran across all the batteries and grabbed them from both sides at the top. But it wasn’t secure on one side. We needed to disconnect both hold-down J-bolts, reposition it squarely over the batteries and then reinstall the hold-down bolts. When in proper position, tighten the nuts at the top ends of the fastening bolts.
Note that there are many connections because of the need to wire all the batteries in parallel on both ground and positive sides to supply the electrical system. There are sometimes even connections joining cable ends together. And some trucks have a separate connector and cable for the engine ECM. Follow all wiring to where it grounds to the frame or component and clean connections there as well. Make sure not to miss any connections, using a marker to mark each one you’ve serviced, if necessary.
Testing the system
The most obvious test is a careful and constant eye on the voltmeter on the dash. If the voltmeter gives consistent readings somewhat over 12 volts with the key on and engine at rest, and a good solid 14 volts with the engine running above idle speed, the electrical system is probably functioning well.
Bruce Purkey of Purkey’s Electric, one of the trucking industry’s top charging system experts, has a slightly more accurate way to test your alternator’s health. The test results are meaningful only if you are already sure that the belt drive and your batteries and cables are in good shape. You’ll need an accurate DC voltmeter.
“You don’t want to see either an increase or a decrease,” Purkey says. “An ideal reading would be 14-14.2 volts at both 1,000 and 2,100 rpm.” If the voltage change is .2 volts or less, the alternator’s regulator is functioning properly. The alternator could still have an amp problem. The above test is only half the total test.
Going beyond such simple tests puts you in the major leagues when it comes to test instruments. Even the relatively straightforward digital battery analyzer Denis Granville showed us costs about $700. This measures battery impedance, which is a little like resistance and gives an excellent indication of how much plate surface is still working. As batteries age, parts of the plates go bad and, eventually, capacity drops to the point where you won’t start, so this tells you a lot.
In spite of the sophistication of such a test instrument, Purkey much prefers a combination unit that also puts a heavy load on each battery and measures output voltage to make sure the unit can handle heavy stress. He describes it as being similar to a treadmill stress test your doctor does on your heart. But such instruments go for about $1,000. One thing is for sure, and he and Granville agree on this one: Batteries must be disconnected and tested one by one to get meaningful results. If you take the truck in to have your batteries tested, make sure they do the test this way.
Another test a technician with the right equipment can make is a loaded alternator test. Purkey says a good alternator will be able to achieve full output in most cases by the time the engine reaches 1,000 rpm. Knowing how much power the alternator can make at various rpms is a great test of its health. It’s easy to install a clip-on ammeter to get the amperage readings in doing such a test, but the expensive part is acquiring a gadget called a carbon pile to put a heavy enough load on the alternator. The load must be heavy enough to drag the voltage all the way down to 12 volts throughout the test. You might want to suggest such a test to whoever is diagnosing your system.
One, two, three!
Since alternators and batteries often function normally till just before a sudden failure, it’s absolutely necessary to approach troubleshooting from the right perspective. Purkey stresses a “one, two, three” procedure that tests the batteries individually with the above-mentioned combination test, then the cables and finally the alternator. Many a technician or do-it-yourself trucker has replaced his batteries or alternator only to find the real problem was a cable that wasn’t carrying the current between the components. While do-it-yourselfers can do a few simple checks, when you suddenly run into trouble, the smartest thing to do is to get an experienced pro to test the system for you. Testing a cable right means applying a heavy load and accurately measuring voltage drop from one end to the other. It’s a test well beyond the reach of a do-it-yourselfer’s bank account and possibly his technical capabilities.
What Purkey’s valuable advice tells us is that you need to find somebody who can do these tests this way or risk spending a lot on the wrong repair. This means finding somebody with a good reputation and being willing to commit to paying for a couple hours’ labor to make sure the job gets done right the first time.
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