HEAVY DUTY ALTERNATORS The rotor is electrically magnetized by a small current flowing through it via brushes riding on smooth slip rings. Alternating  current  is  produced  as  the  magnet  poles  of  the rotor   pass   through   the   coil   windings   of   the   stator.      For increased   capacity,   there   are   twelve   (12)   magnetic   poles incorporated  into  the  rotor  and  three  (3)  separate  windings  in the  stator.    Since  alternating  current  is  produced  as  the  rotor passes the coil windings of the stator, increased engine speed produces more current. The    battery    stores    only    direct    current    and    cannot    use alternating  current.    For  this  reason,  rectifier  assemblies  are used  to  convert  alternating  current  produced  in  the  stator  to direct   current.      Rectifiers   consist   of   silicon   diodes   which function  as  electrical  switches  and  permit  current  flow  in  only one direction. The rectifier diodes are mounted in aluminum castings, called heat sinks, which are finned to dissipate heat. A built-in solid state voltage regulator controls alternator output and the battery’s state of charge.  A lead from the vehicle’s key switch provides turn-on voltage to the voltage regulator. The regulator senses when the battery has received sufficient charge and then reduces the "field" (magnetizing) current flow to  the  rotor.    Reducing  the  field  current  flow,  in  turn,  reduces alternator output. When   headlights   and/or   accessories   place   a   load   on   the battery,  the  regulator  increases  the  field  current  flow  to  the rotor, thereby increasing alternator output. PREVENTIVE MAINTENANCE Mounting hardware including brackets and drive belts must be periodically  inspected  and  adjustments  or  repairs  performed as  required.    It  is  important  that  mounting  bolts  and  nuts  be kept securely tightened to maintain belt alignment and prevent vibration damage which will occur if mounting bolts work loose. Vehicle wiring must be inspected at periodic intervals for loose or corroded connections and repairs made as needed. TROUBLESHOOTING 1. Check the drive belts, wiring, and mounting hardware, and make sure that they are in proper working order. 2. Check     the     batteries     according     to     manufacturer specifications     to     insure     that     they     are     in     good condition.        The    batteries    must    be    at    least    75% charged.  If necessary, charge or replace batteries. 3. To  establish  if  the  alternator  is  functioning  properly, connect  an  accurate  test  voltmeter  to  the  alternator output terminals (use a voltmeter capable of measuring    1/100    of    a    volt).        With    all    electrical accessories off, run the engine at approximately 1000 RPM. Voltage reading should be within 13.8-14.2 volts. If the alternator is overcharging, continue with step 7. If a  low  output  condition  is  noted,  then  continue  with step 4. 4. Remove the regulator as shown under DISASSEMBLY section. Remove   and   inspect   the   brushes.      If   brushes   are cracked,  burned  or  worn  to  3/16"  or  less,  then  the brushes  must  be  replaced.    Insure  that  each  brush contact lead has a good connection to the brush and the contact cap. Clean  each  brush  contact  cap  and  the  two  contact pads on the regulator. Reinstall  the  brushes  and  regulator  as  shown  under REASSEMBLY, steps 12 and 13. 5. Repeat  the  test  in  step  3.    If  the  output  voltage  is below 13.8 volts, the unit should be full field tested as shown in step 6. 6. Shut   off   the   engine   and   all   electrical   accessories. Measure the voltage at the alternator output terminals and  make  a  note  of  the  reading.    Connect  a  short jumper  to  the  alternator  NEGATIVE  output  terminal and to a 1.5-2" piece of stiff wire (a piece of paper clip wire is suitable).  Insert the wire in the full field access hole as far as it will go.  See Figure 3. Figure 3 - Jumper Connections for Full Field Test. Run  the  engine  at  about  1000  RPM  and  check  the output voltage.  If the voltage rises rapidly above the voltage  reading  noted  when  the  engine  was  off,  the alternator is OK, continue with step 7. If  the  voltage  rises  slowly  or  remains  the  same,  the alternator is defective.  Continue with step 8. CTS-4043A - Chapter II - Page 3