Battery / Alternator charging query

[Graham King]

Folks, bit of advice from those more in the know than me on car electrical systems. This is on a tin top not the 7, went out to car this morning, car starts fine but alternator/battery warning light is permanently on. 

I’ve measured the voltage across the battery with engine turned off, it’s approx 14.5v, the started car and voltage started to rise, up to about 15.5v, the turned the car off and the voltage still continued to rise, up to about 16.1v. Something clearly isn’t right, I expected to see that the battery wasn’t charging so expected to see the voltage dropping but if anything it appears to be overcharging. 

Am I missing something or is this just another type of alternator failure, the battery appears to be fairly new and the battery indicator is showing fully charged. 

Thanks for any advice

Graham

[Jonathan Kay]

... is this just another type of alternator failure...

That sounds likely.

If the access allows it see if there is a loose or damaged wire at the alternator. Beyond that I can't think of sensible further checks before getting it to an expert.

I'd go to an independent car electrician.

Happy Christmas

Jonathan

[Graham King]

Thanks Jonathan, you’ve confirmed what I suspected, as far as I can tell there are no broken wires, certainly not visible. 

Looks like a visit to local garage tomorrow then. 

Happy Xmas all.

Graham.

[Piers300]

Sounds like the voltage regulator in the alternator is not regulating correctly. 

Piers

[tbird]

yep sounds odd, not in a good way either, but as an aside, i'm not sure how much i would trust your meter, for one thing the voltage , in theory anyway, cannot rise when engine turned off, and i would be very surprised to see a battery read 14.5 v across the terminals, with engine not running.  

but it is obviously something is wrong and as said it sounds like your regulator as piers says, so basicaly the alternator is just putting AC across the battery, the normal classic sign is charge light out at tickover but come on as revs build. however it wouldn't be unusual for it to be on all the time. try not to drive around too much looking for a garage it isn't going to be doing your battery any good, and could cause it to boil .

interesting article here about Batteries/alternators and charge if you are interested

oh and presumeably you know these folk if your battery is fubared, they are pretty quick and prices difficult to beat https://www.tayna.co.uk/

good luck

Tim

[Graham King]

Thanks Tim & Piers, the garage I use is about 4 miles away, I’ll run it round to them tomorrow and leave it with them. The multi-meter I’m using is actually fairly new, I could test it on another car I guess and make sure it’s working ok. 

I’ll give that a go and report back.

Graham