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.
- Make sure the alternator is being driven at full speed mechanically.
- Confirm that all connections throughout the system are clean and tight.
- Check the tightness of all battery and alternator mounting bolts.
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.
- With the engine off, open the hood and check the tightness of all alternator mounting bolts – both bolts fastening the alternator to the bracket and those fastening the bracket to the block or front cover. Look for missing bolts and nuts, too, and replace any missing parts. Bolt torque can be checked with your fingers during your daily walk-around but should be done with a wrench at your standard oil change maintenance interval.
- At the same time, check to make sure the belts and pulleys are properly aligned. Belts should run straight into and out of the pulley grooves, and all the grooves for a given belt in a multi-belt system should be in line with one another. With conventional alternator tensioning systems, misalignment would be caused by a loose pulley that had slid outward on its shaft, loose mounting bolts or, possibly, bent mounting brackets. Correct misalignment to guarantee belt reliability.
- The latest trucks use serpentine belts, which are flat with several small grooves along the inside diameter. These belts get their name from the way they snake around the various pulleys. These systems use automatic, spring-loaded tensioners to eliminate belt tension adjustment and periodic retensioning. They are tensioned where the flat back of the belt runs against the flat surface of the tensioner’s grooveless pulley. A common cause of misalignment is worn bearings in the tensioner that cause it to cock to one side. In this case, the back of the belt will run slightly off the tensioner’s pulley on the engine (rear) side, or the belt may twist slightly, causing it to fray. If you see this, replace the tensioner to prevent premature belt failure.
- Automatic tensioners have an indicator line on the tensioner lever. It should remain lined up between two marks on the tensioner body. One mark indicates the tensioner is turned too tight against its spring and is creating excessive tension. The other indicates it has rotated too far in the direction of spring force so there is no longer enough tension. While belts rarely stretch enough to reach the limit indicated by the second mark, an indicator line located past that one indicates either a severely stretched belt or a new one that is much too long. This means not enough tension and possible slippage. Too short a belt is the only cause of a line to the other side of the first mark. This means excessive tension that would make short work of tensioner and accessory bearings. On alternators with conventional tensioning mechanisms, check where the tensioning bolt runs through the alternator frame, and make sure there are adjusting nuts on both sides and that these are snug. Check belt tension with a tension gauge. If tension is inadequate, loosen all the mounting bolts and nuts, including those on the hinge bolt at top or bottom and then one of the adjusting nuts. Adjust tension with the adjusting nuts and then tighten all nuts and bolts. Make sure all fasteners, not just adjusting nuts, are tight before rechecking tension.
- Inspect the belts carefully for fraying or worn outside edges as you check tension. Twist serpentine belts out with your hand so you can get a good look at the inner surface. Wear typically starts to show where cracks in the ridges between grooves crop up. As wear proceeds, chunks will fall out, indicating a belt on its last legs. Standard V-belts will show a glazed V-surface worn smooth from heat resulting from slippage or cracks, especially in the inner section of the belt. Replace worn belts, and always renew multiple belts in complete new sets.
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.
- The job is done on conventional tensioning systems by loosening all bolts and rotating the alternator as far as it will go toward the engine prior to removing the belts. Replace in reverse order, tensioning the new belt as described in Step 4. New belts with conventional tensioning systems should be installed with just a little extra tension. Their tension should be readjusted after at least 30 minutes of operation.
- Check all wiring connections to make sure they are clean and tight. This means output and ground connections at the alternator and any connections where the ground wire attaches to the frame or engine block. Check with fingers during daily walk-around and with a wrench at oil change intervals. Once a year, disconnect the batteries and then disconnect and clean the alternator connectors and nuts with emery cloth to remove corrosion and minimize resistance to current flow. After cleaning and reassembling snugly, coat the connections with a corrosion inhibitor. This is available in a spray can sold at dealers and parts distributors.
- It’s smart to do the same with starter positive and ground connections, including where the ground wire attaches to the frame.
Routine battery maintenance
- First, remove the top of the battery box. When the battery box is located between the frame rails, as it is on a new Freightliner Columbia, first release the locks and then rotate the deck plate forward on its hinges. Then remove the locknut from the center of the box cover and remove it. On older trucks like a 2000 Century Class Freightliner or any with the battery box bolted to the side of the frame rails, first release and remove the step located next to the deck plate.
“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.
- Check all the battery box bolts where it is bolted to the frame, as a loose battery box is just as bad as a loose battery. Boxes mounted between the rails are sometimes bolted to straps, which are, in turn, bolted to the frame. All these bolts should be inspected during a walk-around and tightened up with a wrench once a year.
- Battery connections corrode, even with modern maintenance-free batteries. At least once a year, disconnect them and clean all the surfaces with emery cloth to remove oxidized metal (it resists the flow of current). Then reassemble tight, coat with white lithium grease and reinstall protective caps. Where caps are missing, replace them. Remember that you may at times end up with a connector having 12 volts on it as you work. Either disconnect all battery positive cables at the battery posts before doing work or make sure not to ground the other end of these cables.
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.
- Clean the tops of the batteries with a solution of baking soda and water. This will remove a film of conducting material that can increase the rate of discharge during a shutdown.
- Reinstall the battery box top and deck plate or step as 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.
- Turn off all electrical loads. Don’t forget any appliances in the sleeper like your refrigerator.
- Run the engine at fast idle for two or three minutes after starting to stabilize the batteries.
- Slow the engine to just off idle, and hold it at a stable 1,000 rpm. You can use the electronic or manual throttle to hold it there.
- Connect the voltmeter across the alternator output terminals. When the reading stabilizes, read it carefully.
- Now, accelerate the engine to governed speed. Read the voltmeter again.
“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.