Voltage Regulator/Alternator or just a new battery?

[redrabbit29]

Hi,

I have a Ford Focus and yesterday I drove home without any issues. But then later the car wouldn't start. Internal lights on, radio but engine wouldn't turn over.

• A friend used a volt metre which showed 11.6volts - too low.
• We then used a charger and after 30 minutes the car turned on without problem.
• However we then tested the volts again - with the car running - and it was just over 15volts.

I've read online that this is bad and suggests a faulty voltage regulator which is part of the alternator.

The battery is old - at least 6 years so due for replacement.

So my question is:

Does it sound like it's the voltage regulator and therefore a bad alternator? Or does it still seem to be a bad battery?

I've ordered a new battery anyway, which arrives on Wednesday. My gut instinct is telling me it's just the battery but that's really just a guess.

Thanks

[Krikkit]

If you're getting over 15V it certainly sounds like the alternator has a fault, and a multimeter having an issue is very unlikely

[redrabbit29]

Krikkit said:

If you're getting over 15V it certainly sounds like the alternator has a fault, and a multimeter having an issue is very unlikely

Is there any easy way of telling if it's the alternator?

After attaching the volt metre and running the engine for about 2 minutes it dropped to 15.01 volts so it may have just been adjusting if that's even possible

[STe_rsv4]

Normal DC voltage when engine is running is between 14V to 15V.
anything less than 14v I would say alternator is goosed.
I would run engine for half hour or so then monitor the battery voltage once the engine has been shut off. If he battery voltage is dropping to below 12V then I would suggest that is where the problem lies.

[Dogwatch]

Krikkit said:

If you're getting over 15V it certainly sounds like the alternator has a fault

Certainly a bit on the high side. See what happens with the fresh battery, it may be that the dying battery is upsetting the alternator and things will settle down after the change.
As said, 14point something volts is the expected charging voltage, enough to overcome the 12v pushback from the battery.