andysmee

When I start up the car the voltage on the PFC shows 14.5V

After 40 minutes driving it slowly drops down to about 13.6V

Why? What regulates it? and can you change it?

preludesh2000

iTrader: (1)

your still in a good range...and alot of things pull voltage...are your fans on, ac on, lights on, you have a stereo in the back, ive seen heat from under the hood make a battery drop in voltage..(if yours is still under the hood)

eld101

13.6 is a normal voltage.

andysmee

thanks for your replies but they don't really answer the question (no offence meant!)

This happens every time I drive the car and whilst 13.6V is a normal voltage I want to understand why it starts so much higher.

All the electrical items that you list are on when I start the car and still on when I stop driving 40 minutes later. The voltage doesn't go below 13.5V on longer journeys so I don't think that there is a trend, it appears to be deliberate - like the charging circuit is built to provide a charging voltage when you first drive the car...

Any ideas?

EDIT: A bit of Googling and I now know the answer, thanks

eld101

There is probably a voltage regulated integrated to the alternator.

1QWIK7

iTrader: (33)

Seems like the ALT is going out.

13.5-13. anything is low voltage for a car thats running.

Should in the in the neighborhood of 14.4-14.6V.

gracer7-rx7

iTrader: (16)

my volts are around 13.9v when the car is running.

andysmee

anyone have a car running lower than 13.8V after driving for half an hour or so?

Improved FD

mine is about 12.1 at idle with the lights and fan on

13.6 once I rev it up

andysmee

Now that sounds low! The regulator should keep the voltage between 13.5 and 14.5 (typically at the higher end while the battery is charging hence the drop after half an hour of driving as the battery equalises the voltage)

dradon03

iTrader: (2)

Mine on the old car was the same. Battery never decharged, so I can't see the alt. dying.

Improved FD

the alternator is going bad when it never achieves 13 V or more