Charging System Output Test The charging system output test measures system voltage  and  current  under  maximum  load.  To  check output   with   a   load   tester,   connect   tester   leads   as described by the manufacturer, as you may have either an  inductive  (clip-on)  amp  pickup  type  or  a  non- inductive   type   tester.   Testing   procedures   for   an inductive type tester are as follows: With the load tester controls set as prescribed by the manufacturer, turn the ignition switch to the RUN position. Note the ammeter reading. Start the engine and adjust the idle speed to test specifications (approximately 200 rpm). Adjust  the  load  control  on  the  tester  until  the ammeter reads specified current output. Do not let voltage drop below specifications (about 12 volts). Note the ammeter reading. Rotate  the  control  knob  to  the  OFF  position. Evaluate the readings. To calculate charging system output, add the two ammeter  readings.  This  will  give  you  total  charging system  output  in  amps.  Compare  this  figure  to  the specifications within the manufacturer’s manual. Current  output  specifications  will  depend  on  the size  (rating)  of  the  alternator.  A  vehicle  with  few electrical  accessories  may  have  an  alternator  rated  at 35 amps, whereas a larger vehicle with more electrical requirements could have an alternator rated from 40 to 80  amps.  Always  check  the  manufacturer’s  service manual for exact values. If  the  charging  system  output  current  tested  low, perform a regulator voltage test and a regulator bypass test  to  determine  whether  the  alternator,  regulator,  or circuit wiring is at fault. Regulator Voltage Test A  regulator  voltage  test  checks  the  calibration  of the voltage regulator and detects a low or high setting. Most   voltage   regulators   are   designed   to   operate between 13.5 to 14.5 volt range. This range is stated for normal  temperatures  with  the  battery  fully’  charged. Regulator voltage test procedure is as follows: Set the load tester selector to the correct position using the manufacturer’s manual. With the load control  OFF,  run  the  engine  at  2,000  rpm  or specified test speed. Note the voltmeter reading and   compare   it   to   the   manufacturer’s specifications. If  the  voltmeter  reading  is  steady  and  within manufacturer’s   specifications,   then   the   regulator setting is okay. However, if the volt reading is steady but  too  high  or  too  low,  then  the  regulator  needs adjustment  or  replacement.  If  the  reading  were  not steady, this would indicate a bad wiring connection, an alternator   problem,   or   a   defective   regulator,   and further testing is required. Regulator Bypass Test A regulator bypass test is an easy and quick way of determining  if  the  alternator,  regulator,  or  circuit  is faulty.   Procedures   for   the   regulator   bypass   test   is similar to the charging system output test, except that the regulator be taken out of the circuit. Direct battery voltage  (unregulated  voltage)  is  used  to  excite  the  rotor field.   This   should   allow   the   alternator   to   produce maximum voltage output. Depending upon the system there are several ways to  bypass  the  voltage  regulator.  The  most  common ways are as follows: Sorting a test tab to ground on the rear of the alternator  (if  equipped). Placing  a  jumper  wire  across  the  battery  and field terminals of the alternator. With a remote regulator, unplug the wire from the regulator and place a jumper wire across the battery  and  field  terminals  in  the  wires  to  the alternator. CAUTION Follow  the  manufacturer’s  directions  to avoid  damaging  the  circuit.  You  must  NOT short or connect voltage to the wrong wires or the diodes or voltage regulator may be ruined. When  the  regulator  bypass  test  is  being  performed, charging  voltage  and  current  INCREASE  to  normal levels. This indicates a bad regulator. If the charging voltage and current REMAINS THE SAME, then you have a bad alternator. Circuit Resistance Test A  circuit  resistance  test  is  used  to  locate  faulty wiring,  loose  connections,  partially  burnt  wire, corroded terminals, or other similar types of problems. 2-23