Alternators adjust their output voltages based on temperature, as fully charging the lead acid battery in cold conditions (e.g. -20degC) requires voltage of 15...16V (e.g. the magical 14.4V number won't cut it) in order to not sulfate and self-destruct in matter of months, which is exactly why it's normal to have 15V on the system, and quite obviously everything connected to the car needs to deal with it.
It depends on the car. On Toyota Corolla I didn't seen alternator voltage above 14.4V. But on another car type I was seen 15V and more... I'm not sure if these 15V is due to broken/failed alternator voltage regulator, or just by design.
Usually alternator has voltage regulator which can control alternator output voltage. It control it by change current through special alternator coils. Sometimes this regulator is failed and alternator can push high voltage on the battery. In such case it leads to a faster death of the battery due to overcharge. The bad thing is that all works ok, and you can even don't suspect that alternator regulator is failed, you can replace battery, it it also will be dead soon. This is why it is important to check alternator voltage in case if your battery is dead too quickly.
But there is also modern Ca/Ca batteries, which may require higher charge voltage than 14.4V, so it's not easy question.
Yes, 15V looks ok, for all vehicle electronics, because it should survive even higher voltage pulses. But who knows, may be some cars don't like when voltage is 15V and more...
Hi,
It is very interesting that you brought this up because I had talked about this on a forum dedicated to automobiles. The battery voltages on different cars can be VERY different, which does not make sense at all.
On a Hyundai I once had, the voltage was a max of 14 volts, which never charged the battery enough. I had to bring the battery into the house to charge on a battery charger about once every three months or so.
Also on a Volvo, max 14 volts.
On a Ford Mustang, the max voltage was about 14.2 if I remember right.
On a Buick, the voltage can reach up to 15 volts max, then slowly come down as the battery charges.
From my experience, the lower voltages can only work if the car is driven every day, and it may be questionable at that.
The 15 volt max works the best, because it charges the battery better and also brings the voltage down once the battery gets charged to some degree. That's the best.
Now one more car, an older Toyota, with max voltage around 13.65 volts. That's nuts, but I will test that more in the future because the guy just got a new battery so maybe it charges better with a new battery. If it does not ever go higher than that, then I do not expect the battery to last long unless he charges it manually from time to time. I don't have much data on that one yet though so I will be measuring the voltage from time to time also to see if the 'resting' voltage drops more and more. If it keeps dropping, that's a sign that it is not charging enough.
I have not figured out why these voltages should be that different, and nobody seems to really know there are just guesses out there.
There is one thing that sounds like a 'fact' though, and that is the type of battery. There are the older types and the newer types. The older types are used in older cars and I think they charge better with lower voltages like 14 volts, while the newer ones are for newer cars that can charge better. That seems to be a fact because the different battery types are recommended for the different cars, and the newer type chemistries are not recommended for older cars. This I found out by looking up batteries for different cars. What I do not know is how much of a difference this makes, as the best info I can find says that there is about a 0.1 volt difference between the two, but I don't know how accurate that figure is.
If someone knows more about this variation in automobile max charging voltages now's the time to speak up.