Charging

[davlyn]

Good afternoon,

Can somebody let me know what voltage i should expect to see on a volt meter when placed across the live and earth terminal on my P38 diesel whilst the vehicle is ticking over.
Should it rise significantly when the engine is revved?

sorry if its a stupid question, I'm just trying to work out if the alternator is charging correctly before I fit a new battery.

I look forward to your reply,

Dave

[trex100]

you sould see any thing between 12-14 ish volts

when all electrics are on it should just got to just under 15 at the most even when reving

hope this helps figures are not exact

[jackdw]

A fully charged battery should, in general, read out at 12.7 volts. When ticking over, or when revving quickly, it should rise to 14.4/14.5 and no more. Anything above will damage the battery, anything below and the battery won't be getting charged enough.

[pistnbroke]

To be more specific.....First if you charge your battery and let it sit for 24 hrs then if you dont have 12.5v then the batterys is suspect.
Readings at idle and with lights etc on are meaningless ....go for a short drive and then without stopping the engine read the battery volts at about 2000 rpm ./ should settle to 14.4v . If below this then the voltage regulator is faulty.
This does not apply to ECU controlled alternators which need a different technique.