Technical A newbie with an alternator question

[aross]

Hi,

I have an auto stop/start 2023 Ducato with a smart alternator (I'm pretty sure it's not uprated as it's a small van) and I'm getting an output of 12.7. Should I be expecting more than this?

Any info gratefully received!

 

[Communicator]

12.7V may be OK if battery is already fully charged, but you would need a higher voltage to recharge the battery. Forum member @Reg 65 has had some experience with smart alternators.

 

[Reg 65]

To check a smart alternator you need a voltmeter you can see safely when you are driving
like this (weblink)
so that you can see the voltage rise when you take your foot off the throttle and the vehicle momentum is turning the engine - thats when its designed to charge the battery - at up to about 15 volts
If the battery is over about 80% charged the alternator will only charge it when the vehicle momentum is turning the engine.
It won't charge when the vehicle is stationary or the engine is under load - the battery may even be discharging with the voltage down to about 12.2 with the engine running - and nothing wrong with that. The idea is that it gets its energy to charge the battery for nothing - like when you are going downhill, not when you are using diesel to turn the engine.
So the usual method of checking a (conventional) alternator charge rate when the vehicle is stationary could lead you to think the alternator is faulty when there is nothing wrong with it - and changing the alternator is a big expensive job!

 

[aross]

To check a smart alternator you need a voltmeter you can see safely when you are driving
like this (weblink)
so that you can see the voltage rise when you take your foot off the throttle and the vehicle momentum is turning the engine - thats when its designed to charge the battery - at up to about 15 volts
If the battery is over about 80% charged the alternator will only charge it when the vehicle momentum is turning the engine.
It won't charge when the vehicle is stationary or the engine is under load - the battery may even be discharging with the voltage down to about 12.2 with the engine running - and nothing wrong with that. The idea is that it gets its energy to charge the battery for nothing - like when you are going downhill, not when you are using diesel to turn the engine.
So the usual method of checking a (conventional) alternator charge rate when the vehicle is stationary could lead you to think the alternator is faulty when there is nothing wrong with it - and changing the alternator is a big expensive job!

Thank you very much for the very detailed reply. Obviously a lot more complicated than I thought!