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THE OBJECTIVE OF
THE FOLLOWING TEST IS TO DETERMINE IF AN ALTERNATOR OR
GENERATOR PRODUCES AS MUCH CURRENT AS THE ACCESSORIES USE.
FOR EXAMPLE, IF THE BLOWER MOTOR REQUIRES 20 AMPS WHEN
OPERATED ON HIGH, THE HEADLIGHTS REQUIRE 10 AMPS AND THE
IGNITION SYSTEM DRAWS 3 AMPS, THEN THE ALTERNATOR MUST
GENERATE AT LEAST 33 AMPS TO PREVENT THE BATTERY FROM
DISCHARGING.
WITH ALL ACCESSORIES ON AND THE ENGINE RUNNING AT IDLE SPEED,
THE BATTERY WILL DISCHARGE. CURRENT IS FLOWING OUT OF THE
BATTERY IN ONE DIRECTION. BY INCREASING THE ENGINE SPEED WELL
ABOVE IDLE, THE ALTERNATOR SHOULD PRODUCE MORE CURRENT THAN
THE ACCESSORIES REQUIRE. WHEN THIS HAPPENS, CURRENT IN THE
BATTERY CABLES WILL REVERSE.
THE �MAG-PROBE� WILL DETECT THIS CURRENT REVERSAL. THE
HIGH/LOW SENSITIVITY RING MUST BE ATTACHED TO THE �MAG-PROBE�
IN ORDER TO DETECT A CURRENT REVERSAL. TO ATTACH THE HIGH/LOW
SENSITIVITY RING, SEE PAGE 2 OF THE GENERAL OPERATING
INSTRUCTIONS.
CAUTION � TO PREVENT
DETECTING MAGNETIC FIELDS GENERATED BY THE ALTERNATOR, STAY AT
LEAST ONE FOOT AWAY FROM THE ALTERNATOR DURING THE FOLLOWING
TEST:
AS YOU CAN SEE IN THE ABOVE ILLUSTRATION, A TEST LOOP HAS BEEN
MADE IN THE NEGATIVE BATTERY CABLE. INSTRUCTIONS FOR MAKING
THIS LOOP WILL BE EXPLAINED LATER IN THIS PROCEDURE.
IN THE ILLUSTRATION, A SMALL GROUND WIRE IS CONNECTED FROM
POINT "A" TO THE NEGATIVE BATTERY CABLE BETWEEN THE TEST LOOP
AND THE BATTERY POST. IF YOUR CAR DOESN'T HAVE THIS SMALL
GROUND WIRE, GOT TO STEP #1 AND USE THE NEGATIVE BATTERY CABLE
FOR TESTING.
IF YOUR CAR HAS SMALL GROUND WIRE, DISCONNECT IT FROM POINT
�A� AND CONNECT A NEW WIRE FROM POINT �A� TO POINT �B�. ADDING
THIS WIRE CAUSES THE TOTAL CURRENT TO FLOW THROUGH THE TEST
LOOP. NOW YOU MAY GO TO STEP #1.
NOTE:
IF YOU HAVE A PROBLEM USING THE NEGATIVE BATTERY CABLE, THEN
USE THE POSITIVE BATTERY CABLE FOR THE TEST LOOP. BUT MAKE
SURE THAT THE ALTERNATOR OUTPUT WIRE ISN�T CONNECTED BETWEEN
THE TEST LOOP AND THE POSITIVE BATTERY POST.
STEP 1.
MAKE A LOOP ABOUT THE SIZE OF A QUARTER IN THE SELECTED
BATTERY CABLE. (SEE ILLUSTRATION.)
IN ORDER TO MAKE A TEST LOOP IN A LARGE BATTERY CABLE, IT MAY
BE NECESSARY TO DISCONNECT THE BATTERY CABLE FROM THE BATTERY
POST, MAKE THE TEST LOOP, THEN RECONNECT THE CABLE. USE
MASKING TAPE OR ELECTRICIANS TAPE TO HOLD THE TEST LOOP
TOGETHER.
MAKE SURE THE ENGINE AND ALL
ACCESSORIES ARE OFF.
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WITH THE HIGH/LOW SENSITIVITY RING ATTACHED, INSERT THE
�MAG-PROBE�S� TIP INTO THE TEST LOOP UP TO THE HIGH/LOW
SENSITIVITY RING IN ONE DIRECTION THEN IN THE OPPOSITE
DIRECTION. THE LED SHOULD REMAIN OFF. IF YOU HAVE A CURRENT
DRAIN OF MORE THAN 2 AMPS, THE �MAG-PROBE�S� LED WILL TURN ON.
THIS DISCHARGE CONDITION IS USUALLY CAUSED BY A PARTIAL SHORT
IN THE WIRING OR A SHORT TO GROUND IN THE ALTERNATOR.
IF THIS OCCURS, TEST THE ALTERNATOR FOR SHORTS TO GROUND BY
FOLLOWING THE INSTRUCTIONS ON PAGE 1 OF THE AUTOMOTIVE
OPERATING INSTRUCTION. THIS PROBLEM MUST BE SOLVED BEFORE
YOU CONTINUE.
STEP 2.
BEFORE YOU START THE TEST.
A. CHECK THE BATTERY
B. CHECK THE FAN BELT FOR TENSION AND WEAR (Slippage)
C. CHECK BATTERY POST CONNECTIONS, GROUND CONNECTIONS
AND ALTERNATOR OUTPUT WIRE. IF YOU HAVE AN EXTERNAL VOLTAGE
REGULATOR, MAKE SURE THE CASE IS GROUNDED TO THE CAR'S FRAME.
STEP 3.
WITH THE ENGINE OFF, TURN ON THE HEADLIGHTS, (HIGH BEAM) AND
ACCESSORIES.
STEP 4.
INSERT THE �MAG-PROBE� INTO THE TEST LOOP UP TO THE HIGH/LOW
SENSITIVITY RING. (SEE ILLUSTRATION.) FIRST FROM ONE SIDE,
THEN THE OTHER. THE LED WILL LIGHT ON ONE SIDE OF THE LOOP.
THIS IS THE DISCHARGE SIDE. REMEMBER IT! MARK IT WITH A DAB OF
PAINT. TURN THE HEADLIGHTS ABD ACCESSORIES OFF.
STEP 5.
REMOVE THE �MAG-PROBE� AND START THE ENGINE. TURN THE
HEADLIGHTS ON HIGH BEAM AND TURN ON THE ACCESSORIES.
STEP 6.
INSERT THE �MAG-PROBE� INTO THE BATTERY CABLE�S LOOP (CHARGE
SIDE) AND INCREASE THE ENGINE SPEED WELL ABOVE THE IDLE. THE
LED SHOULD GO ON OR CONTINUE FLASHING ON AND OFF. (FLASHING
ON AND OFF IS CAUSED BY THE VOLTAGE REGULATOR AND THIS OCCURS
WHEN THE BATTERY REACHES A FULL CHARGE.) THE CURRENT HAS
REVERSED AND THE ALTERNATOR OUTPUT CURRENT IS GREATER THAN OR
EQUAL TO THE HEADLIGHT (ACCESSORY) CURRENT DRAIN. IF THE
LED STAYS OFF, THE ALTERNATOR�S OUTPUT CURRENT IS TOO LOW.
NOTE: WHEN THE �MAG-PROBE�S� LED GOES OUT ON THE DISCHARGE
SIDE OF THE CABLE'S LOOP, IT WILL TURN ON WHEN INSERTED INTO
THE CHARGE SIDE OF THE LOOP. (OPPOSITE FROM THE DISCHARGE SIDE.)
STEP 7.
TURN ON ALL ACCESSORIES, BLOWER MOTOR, HEADLIGHTS, ETC. AND
REPEAT STEP 6 ABOVE.
IF YOUR ALTERNATOR FAILS THIS OUTPUT CURRENT TEST, USE THE
ALTERNATOR TROUBLE SHOOTING INSTRUCTIONS TO LOCATE THE
PROBLEM.
WITH THE TEST LOOP IN PLACE, IT�S EASY TO TEST YOUR CAR�S
CHARGING SYSTEM ANYTIME YOU SUSPECT A PROBLEM.
THIS APPLICATION NOTE MAY BE USED TO TEST CHARGING SYSTEMS IN
AIRCRAFT, BOATS, MOTORCYCLES, ETC. HOWEVER, LIGHTS, DC MOTORS,
HEATERS, ETC., MUST BE TURNED ON WHILE PERFORMING THE TESTS.
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