Alternator voltage

[schizo]

Hi,

I own a 1.6 HDi Citroen C4 -2011 model.

I'm having some issues with the alternator and I'm a bit curious what an ok voltage is when the battery is fully charged?

[xantia_v6]

These vehicles have a "smart" alternator controlled by the engine ECU and the output voltage reduces when (the ECU thinks that) the battery is fully charged. Under these conditions, expect to see about 12.8V, but with the alternator output current adapting to match the load if lights or other accessories are turned on.

Note that the ECU can mis-judge the state of the battery when the battery gets a bit old, even if it still has adequate capacity.

[schizo]

The reason I'm asking is because I'm seeing 14.8v which I think is too much.
The battery is brand new.

I'm also having some issues where the battery is not getting charged properly.

It all starts that the car throws a "Reversing lamps failure", then after driving a bit it throws "Gearbox fault" and sometimes also "Engine fault".
The battery voltage is then always <12.5v and the errors disappear after I've charged the battery fully.

What could be amiss here?

[Kees]

You didn't say anything about the kilómetros of the car.
Last time I had some problems with the alternator, when I disassemble him I noticed that the brushes are faulty, but also the Copper rings are gone, but even so the output was >12 V, but with the new one it was 14,5 Volt.

[schizo]

The car has 210000+ kilometers on it.

So it might be the, very expensive, alternator?

[wurlycorner]

14.8 does sound a little high (14.4 was the norm in old-skool non ‘smart’ alternator days) but what’s prompting you to test it? Have you got some other fault symptoms on the car that suggested a problem?
What do you get if you measure voltage in AC out the back of the alternator?

[schizo]

As I wrote previously.

”I'm also having some issues where the battery is not getting charged properly.

It all starts that the car throws a "Reversing lamps failure", then after driving a bit it throws "Gearbox fault" and sometimes also "Engine fault".
The battery voltage is then always <12.5v and the errors disappear after I've charged the battery fully.
”

[wurlycorner]

I suggest you get the battery properly tested, check the output from the alternator for AC and inspect the main vehicle earth points in the engine bay.

[schizo]

Battery is brand new.
Earth points looks fine and the negative cable as well.

You say check AC output from the alternator. I will try to measure that tomorrow. Do I have to measure on the alternator or is it ok to measure on the positive cable by the battery and the chassie?

[wurlycorner]

Measure it at the output of the alternator. If you measure it at the battery it’s generally more smooth anyway.
It’s not a totally reliable test tbh, but sometimes it does show up a problem.