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Heavyduty Drop
is my alternator bad?
my alternator will start out on crank up @ 14.4 volts but headlights or airconditionaire knocks it down to 13 or less. i just got a new heavyduty battery month ago but i also was running a highwatt sound system. is it possible for the alternator to be bad if it starts out @ 14 and drops to 12 or so?
There are several factors that cause the problem you are having. Not knowing the type of car and amperage rating of the alternator, I can only venture to guess that your high power sound system is causing a majority of the loading problems.
Keep in mind that your alternator is trying to maintain a steady level of current to the following high current drains:
Ignition system
Fuel injectors
Fuel pump
Air conditioning compressor clutch
Headlights (when in use)
These items have a pretty good current draw in contrast to other systems in your car. The sound system may be pushing the alternator to go into what is called a full field situation. When this happens, the current output is at its maximum but it requires a pretty good engine rpm (2000 or better) to help maintain that level.
A lot of voltage regulators in modern cars are controlled by the engine computer in order to limit the amount of loading, and rely on the battery's reserve to keep everything powered up until the engine is at a more stable rpm range. Small cars with 4 cylinder engines have this feature, but it has migrated across the board lately.
Rule of thumb - 13.8 - 14.4V is nominal for an alternator's output. Keep in mind that the voltage will be lower in heat, and slightly higher in cold. Voltage regulators are temperature compensated.
What's important though, is the current output of the alternator. If your alternator supplies 50 amps of current, but your entire car plus sound system draws 80 or 100A, then you are drawing constantly form the battery to make up the difference.
TS-01K Protex Heavy duty Drop safe w/ Dual Key Lock