Shagged Alternator??

[dr_mat 0]

Agreed, but I'd say 13 volts with the engine off is optimistic - ISTR my brand new, fully charged Bosch Silver put out about 12.4v on it's own. In other words, don't worry about it unless it's below 12v, or if it shows any signs of decaying while you're monitoring it. (If it's creeping down 0.01v every 20 seconds or so, it's not going to last very long!)

BTW Costco often sell Bosch Silver batteries, at prices even lower than GSF... (Sorry Stevemac .. ;) )

[Nick_Micouris 0]

just found the batt on GSF for £53 delivered inc vat! sounds fine to me

[Kevin Bacon 5]

Agreed, but I'd say 13 volts with the engine off is optimistic -

 

My VAG battery (Varta I think) dishes out a wholesome 12.8V with the alternator off and my recent new Alty delivers a very healthy 14.3V.

[dr_mat 0]

Yeah, can't remember exactly what mine's putting out, tbh. All I was saying was not to write it off just because it's shy of 13v. If it pushes out 12.4v all day long, then you're on a winner, just as much as if it pushes out 13v.

Last time I checked my alternator it was reading about 14.2v too.

[Kevin Bacon 5]

Aye, and if you see 11.2V or 10.6V as I have in the past..... a new battery is generally a wise investment :lol:

[dr_mat 0]

Hehe my dead battery was reading 11v just after a charge. 30 minutes later it was down to 7v .. :lol:

[Nick_Micouris 0]

if the batt was diying would the alternator light actually come on?

[dr_mat 0]

Nope, cos the alternator is fine...

[Nick_Micouris 0]

so - do you think I was misdiagnosed and that it must be the alternator?

Sorry - I haven't got a voltmeter to hand. He was sure that it was the battery that was at fault because he said that the alternator was putting out 13.7 volts.

 

I was wondering if it is just a problem with the diode. Basically I didn't want to shell out for a new batt unnecessarily.

His point was that the alternator was charging but the batt was not responding - hence the red light! :?:

[dr_mat 0]

Is the light that smart? AFAIK the light only tells you if the available volts from the alternator drops - it's a warning that the alternator can't provide enough volts/current to run the car (and therefore charge the battery), not an indication of the battery condition.

Ok, reading back through this thread, it looks like:

1) your battery is holding charge and providing 12+ volts - battery is ok

2) your alternator is providing around 13+ volts (even with the warning light on) - alternator is ok

.. but the light still comes on. Looks more like a problem with the warning light's circuit! Perhaps there's a voltage regulator problem on the dash? Anyone seen this before?

[Henny 0]

yup, you are right Mat, The light just shows that the load balance is correct and the alternator is providing power rather than the battery... 8)

[Nick_Micouris 0]

hmm -s o the guy was blatantly just trying to shift a battery, eh!?

not sure how to test/sort this light out - maybe I will just have to lump it :x :(

[dr_mat 0]

Does your dash show any other weirdness? Speedo needle jumping? Fuel gauge unreliable?

Does the light come on/go off relating to engine revs? Is it effected by having the headlights on, or the rear screen heaters or something?

Do the headlights dim significantly when the engine cooling fans come on?

See, it may well be that under light load the alternator is ok, providing 13.8v, but under heavy current load it's struggling.

But if the battery holds charge (as you say, you leave the car for a few days and it still fires the car up ok - be worth checking the volts it produces first mind) then I don't think the battery is at fault.

[Nick_Micouris 0]

No other wierdness, no.

It only happened last night - I think the wipers were slow moving and lights became a little dim.

will have a session in her tonight and see what happens!

[dr_mat 0]

Maybe the alternator just got wet? It was p1ss1ng it down round here, did you go through any big puddles??

[Nick_Micouris 0]

no big puddles BUT 1 week earlier I did take the car for an mot and the nipple that owned the place drove the car through a foot of water as the drains were blocked on approach to the centre and the engine bay was steaming. Could that have caused some damage?

[Nick_Micouris 0]

I meant take the car for an mot - obviously! I should use "preview" more often!! :wink:

[dr_mat 0]

You could edit the post... Well you *could*, until I post this reply... ;)

 

Yes, that could well have messed up the alternator, at least temporarily!! How much use has the car had since the "ploughing through fecking huge puddle" incident?

[Nick_Micouris 0]

It has had a good week's worth of driving! I wonder which bit I could have messed up - can you access the regulator easily on the VR? It was a simple screw-on bit on my mk2 golf!

[Kevin Bacon 5]

A bit of water won't hurt it mate, they're designed to be weatherproof.

 

I've cleaned off my engine after a gunk session - with it running - in the past and shed loads of water got into the alterantor and the engine didn't miss a beat.

 

You can't get to the alternator easily on a VR.... unless you're planning on replacing it, I'd leave it be.

 

If it's giving a constant 13.7V, that's fine.....not much else you can with it really.

[Nick_Micouris 0]

cool - I will leave it be and ignore the light I think!

If the car won't start I will look towards the batt replacement!

thanks very much 8) !

[dr_mat 0]

I would have thought the effect of the water would disappear pretty quickly (I had the same thing happen once). Someone said the regulator isn't separate on the VR alternator earlier on, not sure if this is true or not.

Might be an idea to drive around with a voltmeter attached to the battery terminals for a while. If the light on the dash comes on and the battery voltage still reads 13.5v+ then chances are the alternator is ok and it's a detection problem, which will be a complete PITA :(

[Nick_Micouris 0]

hmmm - yep!

is there a wire that runs from the dash to the alt then?

[Kevin Bacon 5]

The little blue wire I think....