306 - New alternator, now suspect battery?

[jamesgmg]

Had the battery light come on on my 306 1.9D and measured the alternator output direct from the alternator terminals and also measuring off battery terminals, getting 11.3v at idle.

Figured bad alternator so just replaced it with a new one. However the new one is giving the same results.

I've checked the big fuses in the box under the bonnet on the wing, I've checked the continuity of the + cable from alternator to battery and the earth from battery to gearbox.

Now I'm wondering if it's the battery as it's probably 8 years old and 2 of the cells are just below the plates and a bit brown and gunky.

Could a bad battery bring down the voltage with the engine running to 11.3v? The car starts fine.

[Gibbo_Wirral]

Batteries only last around five years. Also check all the earth points.

[jamesgmg]

Just put a new battery in, getting 11.88v off the battery and back of the alternator on idle and 12.20v with some revs. So still low...

[RichardW]

Your volt meter is suspect - if the battery was only making 11.8 V it wouldn't even be able to light a candle, let alone start the engine....

[jamesgmg]

Your volt meter is suspect - if the battery was only making 11.8 V it wouldn't even be able to light a candle, let alone start the engine....

Old Battery left to settle with engine off was 12.4v. Pretty sure the meter is good as have been using it for other things with no anomalies. It's only when the engine is started that it dropped.

New battery idle is 12.6v.

[jamesgmg]

Think we might be getting somewhere... the battery light on the dash doesn't illuminate with ignition. Though once I revved past 3k, it came on. At this point I got 14.2v off the battery terminals.

So I think this has something to do with the exciter wire, and the alternator self exciting at high rpm. I don't know how to check this though yet.

[jamesgmg]

Just checked fuse F28 15 amp - battery light, clock and outside temp display, electric front windows, rear wiper and it had blown! Put in new fuse, blew that too.

So I guess I need to track down what is causing that to blow! Will check the rear wiper relay first as had problems with that last year.

[jamesgmg]

Almost solved this! Disconnected the rear wiper motor which shares this fuse and all is working normally