Issue link: https://read.dmtmag.com/i/25194
BIG RIG BASICS JOHN BAXTER Getting Your Power Back If your engine won’t run and your lights won’t turn on, it may be time to replace your alternator eplacing an alternator is a sim- ple job, but diagnosing elec- trical problems is complex. Don’t replace an alternator until you’ve had it tested and know it’s bad. R ? A standard alternator uses brushes to carry current from the ignition system to the rotor Most trucks today use a pad-mount alterna- tor, like the one shown, for more rigid mounting. Consult your truck’s tech- nical manual or the sup- plier of the unit for infor- mation on bolt torques and for further information on replacing older-style alternators 2 1 WHAT YOU’LL mounted on adjustable brackets. With the engine cool, discon- nect the battery cable connec- tors at the batteries. NEED breaker bar Note the routing of the alternator drive belt around the tensioner, crankshaft pulley and driven accessories. Draw a picture if necessary. Using a breaker bar with a half drive, rotate the belt ten- sioner away from the belt to release tension. Hold it in position, remove the belt from the alternator pulley and release 2 the tensioner. 3 4 When it’s time to replace your alternator, or spec a new vehicle, you’ll have to choose between a brushless alternator and one with brushes. Alternators have a spinning shaft with a coil of wire wound around it called a “rotor.” The rotor sits inside the “stator,” which is a large stationary coil of wire where the main output current that runs your truck is created. to energize the alternator. The resulting “field” current creates the necessary moving magnetic field as the engine spins the rotor. The brushes are metal conductors that rub against smooth rings and, though they last a long time, they are subject to mechanical wear. A brushless alternator is larger and twice as complex, with two sections of the rotor and two sec- tions of the stator. The extra stator section is where the field origi- nates on a brushless alternator. Since it is not moving, the ignition 26 TRUCKERS NEWS MARCH 2011 Note and document the posi- tions of the battery positive connection and smaller electri- cal connections on the rear of the alternator for proper polarity. Using an open-end wrench, dis- connect each connector, includ- ing the ground. If the alternator does not have a separate ground cable, consult factory information for the proper procedure. While supporting the alterna- tor, remove the four mounting bolts attaching it to the engine block. Remove the alternator. BRUSHLESS VERSUS BRUSHED ALTERNATORS system wiring can feed it directly, without brushes. Alternators with brushes often work only until the brushes fail due to mechanical wear. The brushes are its most vulnerable part. So, without brushes and the resulting mechanical wear, the brushless alternator can last significantly longer. Also, because the field coil can be much larger, brushless alternators can create a more powerful spinning field and make more power at low rpm. This design is more complex to build and takes more material, so cost is a lot higher. Brushless alternators are best for use in new trucks, especially where minimal downtime is essential. Alternators with brushes will save on initial cost and are ideal on older trucks which may not have many miles left in them, where a few hours’ downtime may not be critical and where the owner can minimize the cost of repair by doing some of the work himself, possibly even replacing the brushes in his own garage.