Replacement alternator?

[Any1else]

Out for a drive and the red battery light comes on. Get the car home and check the voltage across the battery and it’s a decent 12v but when the car is running it’s 11.5. Is that a new alternator or is it worth trying to fix it?

If it’s a new one, what make? EBAY the place to get it?

 

[ph001]

Worth a quick look to make sure all the wiring around the alternator is secure but very likely duff alternator. I would go for a re-manufactured exchange one from somewhere like West Lancs Auto...

https://www.westlancsautoelectrics.co.uk/

 

[mjennings23]

Out for a drive and the red battery light comes on. Get the car home and check the voltage across the battery and it’s a decent 12v but when the car is running it’s 11.5. Is that a new alternator or is it worth trying to fix it?

If it’s a new one, what make? EBAY the place to get it?

Anything below 12.4v across the terminals is a heavily discharged battery. I know they're described as 12v but a 'full' battery is actually 12.6-12.8v, if its showing as 12.0v then its over 75% discharged, which makes sense if its showing 11.5v when running as the car is drawing power from it.

Best thing to do is check the alternator output directly when the car is running. I assume you have a multimeter as you've measured the battery voltage, so you want to take the airbox out and check the alternator voltage, positive probe to the terminal on the back and negative to the casing. If this shows a good output, check the voltage over the engine bay jump points (positive on the firewall and negative can be any ground, but the jump point is near the passenger strut tower).

If the alternator output isnt 14.2+v or so, its dead.
If the alternator is outputting but the voltage over the jump points isnt 14v+, you have a bad connection either to the alternator or the starter.
If the voltage over the jump points is 14+ but the battery is 11.5, you may have a damaged battery cable. The positive cable does have a blowout fuse built into it, but I believe that would also disconnect the battery from everything so don't imagine this could be the issue i.e. the car wouldnt start.

Depending on the state of battery discharge it may need replacing, at the very least you want to get it on a CTEK or similar and run a recondition cycle to minimise any sulphating of the plates. I had a similar issue, battery got worn down and I've just had to replace it a few months later as it's no longer holding any charge above 12.2v.

 

[colb]

Sounds like the alternator has gone bad, had this happen on my Z3, low output from alternator, use of headlights and next day flat battery, it just about coped with daylight driving but the headlights were too much for it to keep the battery charged. Fitted a new alternator and all was well. Did consider putting a new alternator pack in the old unit but so far not done it, after all the bearings in it will be old and worn so a new pack for about £30 probably not worth it. Shop arounhd for best price replacement. Seems there are few reconditioners around these days, did have a mate who had a small business doing this but he packed it in as current trend by garages is to fit new units and not bother with recons.

 

[Any1else]

Thanks ph001 - I will give them a go. I got a starter motor from them last year and completely forgot they did alternators too.

mjennings23 - great reply. I will get the multimeter out and take accurate readings when the rain stops. I had only taken approx readings to check and see if the the battery was getting over 14v when the car was running. The battery is fairly new (6 months) so hopefully it is ok but I will run teh tests you mention.

colb - I did wonder about getting a new voltage regulator and replacing it but I am not sure that that is the issue. You are right that this is not the obnly thing that wears in teh alternator so I am guessing that a replacement is needed. I will check the voltages and then decide.

 

[mjennings23]

Thanks ph001 - I will give them a go. I got a starter motor from them last year and completely forgot they did alternators too.

mjennings23 - great reply. I will get the multimeter out and take accurate readings when the rain stops. I had only taken approx readings to check and see if the the battery was getting over 14v when the car was running. The battery is fairly new (6 months) so hopefully it is ok but I will run teh tests you mention.

colb - I did wonder about getting a new voltage regulator and replacing it but I am not sure that that is the issue. You are right that this is not the obnly thing that wears in teh alternator so I am guessing that a replacement is needed. I will check the voltages and then decide.

No worries, best to check it's not an issue elsewhere thats causing it first, else you may well end up installing a new alternator and not solving the issue. When it happened to me the connection at the starter motor had worked slightly loose (albeit I had replaced the alternator 6 months prior so was pretty sure that wasnt the issue!).

In terms on the chain on the main power cable, it goes Alternator -> Starter -> Jump points -> Battery, so use that to possibly find any issues, but if you check the alternator and the voltage output isnt right that's going to be the issue. You could just change the regulator and that is likely the part that's gone bad, but at 16 years old you'd be best off swapping the whole unit out for a new or reconditioned one. I believe I got mine from Germany via eBay, a new Bosch unit for around £200.

 

[Any1else]

Across the battery its 11.8v but the light came on last weekend and the battery wont have been getting charged. Its a fairly new battery so I don't think the issue is there.

Across the battery with the engine running its 11.5v.
Directly at the alternator when running its 11.3v
Between the live and earth posts on the car its 8.3v ?? Don't think the cables are loose because I replaced the starter motor when I replaced the battery about 6 months ago but I will certainly check them when I have the airbox out.

I think it points to the alternator so will check ebay and West Lancs.

Thanks for the tips.