Battery drainage.

[adrian996]

Hi all. Ok, here goes. MY 2003 996 with 20k miles. New battery 12 months ago. Fully charged using 5amp charger over 15 hours. When driving the car the volt metre gradually drops off to about 11 volts. Had this confirmed by electrical specialist - there's only 11.6 volts coming out of the alternator. No slipping belts or squealing noises. Battery/Generator warning displayed on OBC. Things got so bad of the way home from electrical specialist that ABS and PSM failure lights came on - due to almost zero battery.

Everything points to the alternator but surely not at this mileage and age? She's booked in to my independent on Monday for investigations.

Any ideas, anyone? Maybe something stopping the charge reaching the battery? My independent tells me that he's only ever had to replace one alternator on a 996 (3.4) and that was because the owner tried to clean the engine bay - with a high pressure hose![]

 

[Diesel130]

I'm sure Richard will be along with a wiring diagram soon, but in the meantime I'd guess it could either be a failed alternator, voltage regulator, wire disconnected, or a failed battery.

 

[adrian996]

Cheers, Martin. Where's that confounded Richard!!!![]

 

[Richard_Hamilton]

My money is on a dodgy alternator. It isn't that uncommon. Porsche do an exchange alternator, which is much cheaper than buying a new one. Make sure your indy looks at the exchange catalogue. There are aftermarket ones, but I woudn't go for one if I was you - I know of a couple of cases where they have been problematic.

 

[adrian996]

Ok. Will do. Thanks a lot.

 

[johnk]

i would have said alternator as whilst i worked at opc replaced quite a few so not uncommon

 

[Black80XSA]

It does depend on how the alternator fails, but in most cases when you switch on the ignition the battery warnign light in the instrument cluster isn't illuminated. This is a health check light for the alternator dependent upon how its wired.

A good alternator should push out 13.7-14.0 volts.

 

[adrian996]

Just for the record - spoke to OPC today and they needed my VIN number to select the correct part as (they say) there are at least three different alternators for the 3.6 litre 996 alone. Anyway, they eventually nailed it down and told me that I had two options; either a new one at £840 + VAT or a recon one at £280 + VAT. Strangely, they said that they both come with a two year warranty. Mmmmmm? Bit of no-brainer that then...?

Interestingly I also spoke to Porsche Shop and they said that the alternator would be "£260 + Vat, mate" without even asking me if the car is a 3.4 or a 3.6. I queried this and the guy told me that they're all the same - and didn't sound too happy about me asking the question either.

The car is going into my indi on Monday for "assessment". Just hopeful that there might be a part of the alternator which is replaceable. []

 

[adrian996]

The plot thickens......I charged the battery fully and reconnected it late last night. I haven't touched the car since. My alarm went off at midday today (Sat) as the battery was completely pancake. The battery is only one year old and is a Varta and has performed faultlessly since I've had it.
All this leads me to think that it's not the alternator - but something else which is draining the battery completely - in one night!?

 

[johnk]

do you have a tracker fitted .
they have been known to drain them.
but then again if you car has been running off the battery and had no charge coming back into it it will not have helped the battery one bit

 

[adrian996]

Hi John. Thanks for your interest. Yes, I do have a tracker (Monitor) and I'm beginning to wonder if it has got something to do with all this. I understand that there's a reserve battery also - in case someone tries to nick the car and removes the battery - and I have heard that these can go wrong and constantly ask the main battery for a charge.

Contrary to popular belief, I just don't think that this is the alternator any more....

 

[NXI20]

If the bridge rectifier in the alternator has developed a fault, it's quite possible for the battery to discharge back through the windings. Disconnect the alternator & try again with a charged battery - I reckon you'll find it holds the charge without the alternator in the circuit.

 

[adrian996]

Hi Nick. Thanks for that. My indi is going to take the alternator to a guy who can test it - if I can get the car to my indi.....?!

Adrian.

 

[adrian996]

I've now changed the battery for a brand new Bosch one (from another car that I have) but not disconnected the alternator as I'm not sure how to go about it.
On starting the car: ABS,PSM, Brake distribution and battery/generator messages coming on the OBC - but weirdest of all - the volt metre is now reading 16V +, the needle just goes right to the top. There was also a small amount of battery acid coming out of the battery breather holes! I don't know what the hell to do next!

One other point: The display on the air con goes dim when the engine is running - all the other dash lights seem to be at their normal level...? I haven't run the car for longer than a couple of minutes as I thought that I might be damaging it.

Can anyone please advise? I'm supposed to be driving it to my Indi tomorrow and am very unsure if it's wise to do so..?

I've now got the old battery on charge - away from the car - to see if it holds a charge independently of the car. Not looking good so far, I think that this battery is cooked and I don't want to do the same to my new Bosch one.

Any thoughts would be appreciated.

Adrian.

Update: Looks like the old battery is now holding a charge now that it's off the car.

 

[Richard_Hamilton]

I concur with Nick - it still sounds to me like it might be the alternator. The other possibility might be the ignition switch. That can also produce wierd electrical gremlins.

 

[adrian996]

Update: All fixed now. It was the alternator, my independent got me a recon one - which is essentially as good as new. He's put it down to lack of use and reckons that the brushes may have corroded and stuck to the centre spine. They've then lost their surface when I've started the car and gradually worn down - probably the positive terminal more than the negative. I just hope that there's no damage been done to the computer systems in the car as (although only for a short time) there was over 19V coming from somewhere.

The whole event set me back £470 inc VAT. I'm not worried about the money - just really disappointed with the car. I have a Citroen ZX diesel which has done just over 161,000 miles and is still on its original alternator (..and clutch, and master cylinder, and oil pump, and water pump......)[]

Thanks, as always, to all for your valuable input.