Posted by David Sherman on Sunday, September 09, 2007 at 16:30:25 :
In Reply to: Re: what should a alterantor produce posted by Kaegi on Sunday, September 09, 2007 at 15:52:20 :
Correct. The rough rules of thumb are that at room temperature, a "12 volt" lead acid battery, fully charged, with no load, should measure 12.6 volts. You can safely charge it forever at a constant voltage of 13.8 volts without over-charging, and an alternator output as high as 14.5 volts is probably okay in a modern system with lots of electrical loads. Above 14.5, you'll loose water from the battery. Below 13.8, it'll never quite get fully charged. Although modern alternators will charge a bit at idle, you should rev up the motor to measure the maximum voltage.
Ideally, these voltage would go up a bit at high temperatures and down at lower temperatures, though I don't believe most automotive voltage regulators account for temperature.