TECH TIP FOR NOVEMBER/92

IF A CUSTOMER SAYS "MY BATTERY WENT FLAT", THE FIRST THING YOU ASK IS:
1) DID IT GO FLAT WHILE THE CAR WAS RUNNING, OR WHEN IT WAS
  PARKED?
2) IF IT WAS PARKED, FOR HOW LONG?
3) HAS THE BATTERY EVER GONE FLAT BEFORE? HOW OFTEN?
4) HAS ANYONE USED THE CAR FOR BOOSTING RECENTLY? HAS ANYONE
   OTHER THAN YOU DRIVEN IT LATELY, SAY, JUST BEFORE THIS
   PROBLEM OCCURRED?
5) HAS THE CAR BEEN WORKED ON RECENTLY? BY WHOM AND WHAT DID
   THEY DO?
IF THE BATTERY WENT FLAT OVERNIGHT OR OVER 2-3 DAYS THEN
THERE IS OBVIOUSLY AN EXCESSIVE DRAW. (IF THE VOLTAGE DROPPED
BELOW 6VTS., PARTICULLARY IN COLD WEATHER, THE BATTERY MAY NEVER
HOLD A CHARGE PROPERLY AGAIN.)

MANY NEW CARS HAVE A CONTINUOUS DRAW CALLED A PARASITIC DRAW,
EVEN WHEN THE CAR IS SHUT OFF. G.M.'S INTERNAL REGULATOR
CONTINUOUSLY DRAWS 1-2ma (MILLIAMP OR 1/1000 OF 1 AMP).
SOME PARASITIC DRAW IS TO BE FOUND IN ALMOST EVER CAR TODAY
AND IS ACCEPTABLE, BUT HOW MUCH IS ACCEPTABLE?

GENERAL MOTORS HAS A FORMULA TO CALCULATE THE ALLOWABLE
PARASITIC DRAW A BATTERY CAN TOLERATE. MULTIPLY THE RESERVE
CAPACITY BY .25, YOUR ANSWER WILL BE IN ma.  A BATTERY WITH 80
MINUTES RESERVE CAPACITY HAS AN ALLOWABLE DRAIN OF 20ma ( 80 X
.25 = 20ma)

HERE ARE SOME OF THE APPROX. VALUES FOR SOME COMMON THINGS
WITH CONTINUOUS DRAWS:
DIGITAL CLOCK            3-4ma      QUARTZ CLOCK           7ma
VOLTAGE REGULATOR        1-2ma      RADIO MEMORY           3ma
ENGINE COMPUTER          5-9ma      MEMORY SEAT            3ma
 

REMEMBER TO ALLOW SUFFICIENT TIME FOR THE DELAYED TURN OFF
SYSTEMS TO "TIME OUT", BEFORE CHECKING FOR PARASITIC DRAW (FULLY
LOADED CHRYSLERS CAN TAKE UP TO 55 MIN.), OR YOU WILL GET AN
ABNORMALLY HIGH READING. ANY DRAW ABOVE APPROX. 50ma IS TOO MUCH AND MUST BE CORRECTED.

MANY OF YOU USE A SMALL 9VT. BATTERY THAT PLUGS INTO THE
CIGARETTE LIGHTER TO KEEP THE COMPUTER AND DIGITAL SYSTEMS
ENERGIZED WHILE YOU SERVICE THE BATTERY OR CHARGING SYSTEM.
ON SOME AUDI'S AND VW'S THE USE OF THESE DEVICES CAN
ACTUALLY TRIGGER THE VEHICLE'S AIR BAGS.
I SUGGESTS THAT THE AIR BAGS BE DISCONNECTED BEFORE USING
SUCH A DEVICE.

RUMOUR HAS IT, THAT THE TECHNICIAN WHO DISCOVERED THIS FACT,
HAD THE VW MONOGRAM IMBEDDED IN HIS FOREHEAD FOR A WEEK!!!
REMEMBER!!!

1/10TH OF YOUR LABOUR CHARGE IS FOR TURNING THE SCREW, THE
REST IS FOR KNOWING WHICH ONE TO TURN!!!!!

DISCONNECTING THE BATTERY CABLE WITH THE ENGINE RUNNING WILL
GIVE YOU NO USEFUL INFORMATION ON THE ALTERNATOR. IT WILL,
HOWEVER, GENERATE A 180©240 VT. SPIKE IN A SYSTEM WITH 100 VT.
DIODES.

FOLLOWING THIS PRACTICE WILL GIVE ME MORE BUSINESS AND HELP
ME MAKE IT THROUGH THE WINTER. KEEP UP THE GOOD WORK!!!