Since I've added a digital voltmeter in my XF, I've noticed a variation in the voltage being put out, while running, to be between 13.8 and 14.2. It seems to be higher in the beginning and tapers off as the car has run for a while. My question is....does our alternator/regulator, automatically adjust its output to the lower voltages after the battery tops up, and if so do all modern alternators do this? The voltage doesn't seem to be dependent on the rpms at the time. I never paid too much attention to the charging aspect, because most of the cars I've had utilize "idiot" lights. Just askin ...

 

Don't know, but I have noticed the same thing : 13.8 - 14.2 while running.

 

Howard, that is fairly typical of most charging systems on most cars. It is more controlled by the built-in regulator than alternator. Some will have a larger range, while others may have a more constant voltage.

James

 

I'd say you got it right.

 

Reference the voltage variation.....
Also take into account, that to crank and start a 3.2 litre engine requires ENOURMOUS current and energy from the battery.
This used power has to be replaced by the alternator, and the alternator can only do this by overcoming the opposing battery voltage to get the Amps back into the battery.
Once the cranking amps are replaced back into the battery, the battery and alternator voltages will equalise and settle down.

What you have discovered and noticed is perfectly normal.

 

Appreciate all the input ..... Newbies, take note, that eventho I've been around on the forum for a while, and own 2 XFs, even the most inane questions are answered by very friendly folks.

 

Charging voltage is a function of several things including the temperature of the car. Colder will go as high as 15 volts as the car will need assistance there, warmer it will be lower. Deals with the chemistry of the battery and anticipated loads. Woody

Set your clock forward.....

 

Totally agree, there is a wealth of knowledge here, and it saves us all our hard earned $$$ / £££.

I have saved a fortune with some of the advise shared here - great people, great site, and its nice to be a part of it and enjoy our vehicles.

Regards
Grant B - Southern England

 

+1, the best folks to help people with their XF's. Have saved many peeps many denominations of their currencies!