I noticed when I was changing my oil the other day there was some lead sulfate buildup on my Ranger's positive battery terminal. I checked the battery with my multimeter this morning and it read 12.7 Volts. I started the engine and let it run until it came down off of the high start-up idle and checked the voltage again. The voltage read 14.7 volts with nothing on. Is the alternator overcharging? The cluster battery guage reads in the middle of the range when running.
The battery's a year old, and replaced a 7 year old battery that had a lot of sulfate buildup as well. I attributed it to old age at the time.
Nope. That's a normal charging voltage.
Boil some water and pour it over the terminals. It will dissolve the residue.
It is normal for modern charging systems to reach voltages as high as 15.5V, and as low as 12.5V
Really? I was under the impression that really anything over ~14.5V is overcharging, since a fully charged 12V battery should read 12.7-12.8V, and the alternator voltage only needs to exceed the voltage in the battery to charge. The residue coming back on a new battery's positive terminal is what got me wondering if there might be an overcharge issue.
not true.
Old systems that used a single voltage (~14.5V) to charge were too crude. When the battery was depleted, they would charge too slowly. When they were full, they would overcharge. When the vehicle accessories demanded more power, alternators couldn't keep up. Modern systems use microcontrollers to monitor all these conditions, and adjust the charge voltage on the fly to adapt to changing conditions.
That's on the high side of normal at idle. What is the voltage when the engine is running at cruising speed, around 2000 rpm?
Overcharging would be what I experienced in a car several years ago when the voltage regulator went kinda sorta funny in the head was putting out nearly 20 volts. If yours is staying under 15 I wouldn't worry about it.
I'll check it out when the rain goes away, it's been a dreary, soggy stretch since Friday where I live. I thought it was odd a new battery would be sulfating up top after a year.
Yes, 14.7 volts is normal when the engine is running. Realize that these car batteries need around 14 volts to begin charging. But if it gets past 15 volts, then the battery will discharge excess gases and cause corrosion on the terminals.
It might be the computer just needs an update the alternator is thinking that is is still the old battery and is charging the new one like I'd was doing the old one
Sounds like normal idle/running voltage to me. Just put a baking soda/water slurry on it and wash it off.
Normal,
get you some of those little pads at the auto store and install them under your battery cable connectors.
