TECH TIP FOR JANUARY, 1996

CAN YOU BELIEVE IT!...1996 DOESN'T TIME FLY WHEN YOU'RE HAVING FUN? (SOMEONE, PLEASE, TELL ME WHEN IT STARTED, THE FUN THAT IS)

THE "SI" SERIES OF GM ALTERNATORS INCLUDES THE FOLLOWING DESIGNATIONS: 10, 12, 15, 17, 20, 21, 25, 29, 30, & 40 SI. ALL THE DESIGNATIONS FROM 20SI & UP ARE USUALLY FOUND IN HEAVY DUTY APPLICATIONS. ONLY THE 10, 12, 15, 17 & 21SI HAVE BRUSHES, THE REST ARE OF THE BRUSHLESS VARIETY. ON THE BRUSH STYLE ALTERNATORS THE WIRING AND OPERATION IS THE SAME. THE LOWEST 4 DESIGNATIONS ARE FOUND MOSTLY IN AUTOMOTIVE APPLICATIONS AND THIS TECH TIP WILL CONCENTRATE ON THEM.

ALL THESE ALTERNATORS HAVE A 2 PIN PLUG IN FOR THE REGULATOR, ON THE SIDE OF THE CASE AT THE END FARTHEST FROM THE PULLEY, AND THE CASE IS USUALLY LABELLED 1 OR R AT 1 PIN & 2 OR AT THE OTHER. THE HARNESS CONNECTOR USUALLY HAS A SMALL WIRE (USUALLY WHITE OR BROWN) & A LARGER ONE (ALMOST ALWAYS RED), WITH THE SMALL WIRE CONNECTED TO THE #1 TERMINAL AND THE LARGER WIRE, CONNECTED TO THE #2 TERMINAL. THE OPERATION OF THESE TERMINALS IS AS FOLLOWS:

PIN# 1 TURNS THE ALTERNATOR "ON" BY USING A FEED FROM THE IGNITION SWITCH, THROUGH THE "IDIOT LIGHT" TO GROUND INSIDE THE ALTERNATOR. THIS MEANS THAT IF THE IDIOT LIGHT DOES NOT COME ON WITH THE KEY ON AND THE ENGINE NOT RUNNING, THAT THE ALTERNATOR IS PROBABLY NOT GOING TO CHARGE. SOMETIMES THERE IS A RESISTOR INSTALLED IN PARALLEL TO THE IDIOT LIGHT TO TURN THE ALTERNATOR ON ANYWAY, BUT THIS IS NOT A FIRM RULE. IF THE LIGHT COMES ON, IT MEANS THAT THE ELECTRICAL CONNECTION FROM THE DASH TO THE ALTERNATOR, AND THROUGH THE ROTOR TO GROUND IS COMPLETE. ONCE THE ALTERNATOR STARTS TO CHARGE, FULL OUTPUT VOLTAGE APPEARS AT THE #1 PIN, AND AS WE ALL KNOW IF THERE IS EQUAL VOLTAGE ON BOTH SIDE OF A BULB, NO CURRENT CAN FLOW SO THE LIGHT GOES OUT.

THERE ARE TWO POTENTIAL PROBLEMS HERE, FIRST; WHEN THE ENGINE SHUTS DOWN, THE FEED TO THE #1 TERMINAL MUST SHUT OFF OR THE BATTERY WILL GO FLAT, AND SECOND; IF THERE IS A CONNECTION (ACCIDENTAL OR OTHERWISE) BETWEEN THE #1 PIN AND THE "ON" SIDE OF THE IGNITION SWITCH, YOU WON'T BE ABLE TO SHUT THE CAR OFF WITHOUT UNPLUGGING THE REGULATOR.

PIN# 2 IS THE BATTERY SENSE TERMINAL. IT IS THE POINT AT WHICH THE REGULATOR "SEES" THE CONDITION OF THE BATTERY AND ADJUSTS THE CHARGE RATE ACCORDINGLY. THIS TERMINAL MAY BE LIVE AT ALL TIMES, SINCE IT IS NOT CONNECTED TO GROUND.

IF THE VOLTAGE IS LOW ON THIS PIN, THE CHARGE RATE WILL BE INCREASED TO COMPENSATE, AND LIKEWISE AS SYSTEM VOLTAGE CLIMBS THE RATE WILL DROP. IF THE CONNECTORS ARE CORRODED, OR THE WIRE IS FRAYED, OR ANYTHING ELSE OCCURS WHICH CAUSES THE REGULATOR TO SEE "LOW" VOLTAGE ON THIS TERMINAL, IT WILL INCREASE THE CHARGE RATE IN AN ATTEMPT TO COMPENSATE. IT DOESN'T KNOW OR CARE THAT THE BATTERY IS AT FULL CHARGE AND WILL BE DAMAGED.ALTHOUGH SOME EUROPEAN VEHICLES STILL SET THEIR CHARGE RATE AT 13.8VT, MOST DOMESTIC APPLICATIONS FEEL THAT 14 - 14.8 VTS IS OPTIMUM.

AFTER SENDING OUT THE DECEMBER/95 TECH TIP, I FOUND A REALLY GREAT ARTICLE ON THE CHRYSLER COMPUTER CONTROLLED CHARGING SYSTEMS, AND CONTACTED THE WRITER TO GET PERMISSION TO RE-PRINT IT FOR YOU. PERMISSION WAS GRANTED AND I HOPE THAT IT WILL START TO APPEAR IN THE JANUARY TECH TIP. I THINK IT WILL TAKE ABOUT 3 TECH TIPS TO GET ALL THE INFORMATION AND ILLUSTRATIONS OUT, SO BE PREPARED, THIS IS DEFINATELY THE BEST I'VE SEEN AND WILL DEFINITELY BE A "KEEPER".