Quote:
Originally Posted by brucepick
I think the alternator's reduced-charging mode is actually a not-charging mode.
A lead acid battery has a "resting" voltage of 12.5V. It will usually settle there if there's no load, or a very low load, like just the computer + maybe the radio running. With alt not charging, it will then gradually drop over a minute or two. A deep cycle battery drops much more slowly. Once the battery voltage has dropped to whatever the ELD circuit's low voltage limit is, the ELD reactivates the alternator to charge the battery.
So I suspect the ELD circuit cuts the alt's output, and the car "coasts" on the existing charge in the battery. In normal use (not with an alt delete mod done to the car) the ELD only cuts the alt output intermittently, so in between those outages the battery is getting topped up.
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One complication for this picture is that I observed 12.5 volts charging on my old battery--the dieing one--under certain conditions. In other words the battery was sitting at say 12.2 volts and I turn the alt on and the voltage goes to 12.5 or thereabouts.