Alternator failure ?

[Sunny43.5]

Hi all my 2005 T5 petrol 2.o litre van is nowadays just staying home more often , the battery goes flat after a prolonged period of time and I,v had to jump start it a few times . I also stick the battery charger on it as well , my question is does anyone know if there is a fuse that maybe controlling the flow of power from the alternator as I no longer see any voltage with test metre at the battery . I have a battery symbol on in the instrument cluster which normally goes off on start up , I found it strange that the alternator may have just stopped working suddenly so I suspected maybe a fuse had blown . Thanks in advance for any suggestions .

[Rebuild]

do you have another battery under the front seats? Maybe its cactus and pulling the main battery down, although theres usually diodes and things in the lines to prevent this

[Sunny43.5]

No single battery only , like I said it sits for prolonged periods of time so radio memory and other small electronic things could be the drain or the battery is getting old and doesn't hold charge .

[heyasam]

If the battery has gone flat multiple times it's probably cactus. Even though charge is trying to go in could still read little or nothing at the battery terminals i think.

[BrianJ]

If the voltage at the battery terminals rises to about 14V when the engine is running then the alternator is working, and it might be a faulty battery or a high discharge when the car is idle.

[Sunny43.5]

Ok update battery is near new so no issues there , but I tried the old tried and true method of removing the battery terminal with engine running . Normally the alternator will keep the car running but the nano second the terminal was disconnected it died , So I,ve ordered a new one online so fingers crossed that works . I,ll update once its in the van , thanks for the hints so far .

[Sunny43.5]

Ok update , new alternator arrived and fitted works perfectly again . Sadly it will take longer for the cuts and bruises to heal than the time the job actually took to do . Talk about awkward to get to , undoing the mounting bolts and the tensioner were easy but trying to get to the main positive cable bolt was total bitch . I spent ages trying to get it into a position where I could undo that one lousy nut , in the end I was dripping blood all over the place as I seemed to get stuck against every sharp fitting in the engine bay . Seeing the battery light go out after starting was so nice .

[BrianJ]

LOL, keeping with good old water cooled VW design then.

[jjhobart]

I'm also having a problem with my battery holding a charge.
The alternator appears to be pushing out 14.2 volts ok, but no or miniscule amps.
I am wondering if it is the regulator?
Asking that question tomorrow at the Auto Electrician.
Replacing the regulator is every bit as bad as changing the alternator apparently - front off gives the best access.
JJ

[BrianJ]

There would be very little amps if the battery was fully charged.

[Manaz]

I'm also having a problem with my battery holding a charge.
The alternator appears to be pushing out 14.2 volts ok, but no or miniscule amps.
I am wondering if it is the regulator?
Asking that question tomorrow at the Auto Electrician.
Replacing the regulator is every bit as bad as changing the alternator apparently - front off gives the best access.
JJ

With car turned off, a battery that's dying will generally do one of two things:

1. Show a lower than 12v voltage (car has to be off to test this, otherwise you're just testing the alternator) - 12v batteries are (generally) made up of a number of cells, each of them contributes to voltage. If a cell dies, then the overall voltage will drop.
2. Show 12v still, but provide low amps - most batteries are given a CCA (Cold Cranking Amps) rating, and as they age, they start to fail to produce it. I've had 650cca batteries provide < 500cca at the end of their life (and closer to 400cca).

Batteries also hate the cold. Winter's a common time to suffer battery failure, and cars will start to take a little longer to turn over as a battery starts to fail and the CCA starts to drop.

There would be very little amps if the battery was fully charged.

Correct. You only get amps if the alternator's actually doing work - there needs to be load on it. If the battery's well charged and the car's consuming minimal electrical power, you'll not see many amps at all.