Troubleshooting Alternator (Hypothetical Situation)
Problem: Customer returns continually because his battery
keeps running down, but all battery and alternator tests pass.
Solutions:
• If alternator reads in the low end of the OK range, it is
working ne. For people driving short distances, however,
the battery may not charge fast enough, causing the battery
to run down slowly. A higher amperage alternator may be
necessary to insure faster charging.
• Some shorting or grounding may occur and slowly drain
battery. Use a low range ammeter and check to see that
no current ows from the battery with engine and all
accessories turned off (including clocks). If current is owing,
locate cause and repair. Look for such things as trunk, hood,
ashtray and glove compartment lights, bad switches, etc.
• Ammeters installed after vehicle manufacture may not
have sufcient wire gauge to carry current without causing
a voltage drop. This can reduce battery-charging rate,
Measure the voltage drop from battery positive to alternator
output terminal. If the drop is greater than 0.5 volts, and all
connections are clean and tight replace all wire between the
two points with wire that is one gauge heavier.
• Aftermarket accessories may add enough load to the
charging system to exceed alternator capacity (i.e., stereos,
telephones, defoggers, etc.). Replace alternator with one of
higher capacity.
Dual Battery System
• When load testing check each battery separately with cables
disconnected, so a problem with one battery is not masked
by another battery.
• Charging system should be checked with both batteries
connected.
• Accessories may be connected to one or both batteries. Be
alert to their wiring differences in testing for problems.
ALTERNATOR TEST
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