Battery warning light lingers on

U

ukrainian

Member
So no sooner was the last problem fixed than the next one appears :) The car was in the garage to fix fried coilpack that was causing the engine to operate in limp home mode. That's all ok now but driving off from the garage, the battery light lingered on for a long time. When I got home, scanned for codes - nothing. But, after restarting the engine the same thing happens - battery light stays on. Left it idling to see if it goes out but then the temperature gauge kept climbing without the radiator fan kicking in this is definitely not what normally happens. I hadn't seen the temperature gauge needle move past 90 degrees before. When it got to 100ish I turned the engine off. I had measured battery voltage, it was 12.3V with engine off and 11.85V when idling which seems low to me. Anyway there were more pressing matters - putting the sprogs to bed, dinner, Love Island :D But after the chores were done, I went for a 20 minute drive. Headlights on, aircon set to "Lo". Probably less than a mile down the road the battery light went out. After a while I parked up and let it idle with headlights and aircon and thankfully the radiator fan did come on without the temperature gauge wandering off past 90 degrees. So it looks like it's not a faulty fan draining the battery whilst refusing to come on. I measured the battery voltage with engine off again and it was now 12.8V according to my uncalibrated old Hilka multimeter, so the alternator is still doing something.

This is not the first time the battery light has been strange. I has lingered on previously once or twice in the last couple of weeks but for a much shorter time, just long enough to be noticible. A couple of times it has stayed on dimly, looked like it was flickering on/off.

So I have questions running theough my mind now. Is the radiator fan not kicking in as it would normally, some kind of ECU response to the battery voltage being low (i.e to keep electrical load to minimum)? Do the symptoms point to battery or alternator problem (slipping belt maybe?)? I think both battery and alternator are original 16 year old parts.
 
Before you buy a new alternator, check the actual output from the alternatior, mine was just the regulator, which is only about £20.
 
Thanks AndyP, will do that. Car's going back in the garage on Friday so should find time to check a few things myself. Do you happen to know what a healthy alternator output voltage looks like? Was also thinking a marginal connection will have the same effect, will need to trace all the wiring.
 
I've seen 13.7-13.8V through the ODBII with the engine running at idle in a 1.4i AUA engined car, assume that's the voltage level maintained by the regulator to positively charge the battery at all revs rather than the 12V the battery sits at? If the regulator isn't working effectively you'll see more rev-dependent variation in voltage output from the alternator.
 
I would say that 13.8v is towards the bottom end, 14.5v when charging would be better. Mine did vary quite a lot, in fact monitoing the voltage through ODB showed it was very erratic, but the voltage was sometimes correct, suggesting that the alternator was capable of producing it and that the regulator was probably at fault.
 
The thick plotens :p Was looking under the bonnet to see how I can get to the unregulated voltage from the alternator - didn't get anywhere with that, the terminals don't look accessible. Google seems to think the regulator and brushes is a single piece anyway so there may not be a way to stick the meter direcly on the brushes. Was wondering also why there is a commutator, the winding is in the stator. Best guess is it's cheper to rectify the current that way, does anyone know?

But there is a new clue nonetheless. Thought I'd check on the battery voltage and it's now showing 13.8V with the engine idling. Intermittent problem with battery voltage. Could be brushes, could be wiring, could be regulator. Unlikely that it's the winding. Probably not the belt I've been told I would have heard it squeal..
 
My battery light was coming on when the voltage was about 13.8-ish, not sure what the threshold is but I'm guessing it's closer to 14v. Check my charts from before. But if your voltage is greater than the resting voltage of the battery, then the alternator miust be working and taking the view that a spinning thing is either spinning or not then there are two options, brushes or regulator and as the brushes come with rthe regulator then I reckon it's a good bet.
 
And squealing can be the belt, or the alternator clutch, could be the belt if the clutch is starting to sieze, like mine did eventually.
 
More clues - battery warning light goes out eventually after I drive off, but can be helped on it's way by revving. Also by revving when stationary. So I just stuck the multimeter on the battery whilst the warning light was still on and then again after I blipped the engine to get rid of it. Before - 12.2V, after - 14V. The curious thing was that it now remained at 14V at idle revs. A 'sticky' problem. Perhaps consistent with worn brushes. Or a perished commutator which would mean new alternator...
 
Just googled alternator working principle, turns out there is no commutator. The brushes are for the secondary winding which is mounted on the rotor. So there is no permanent magnet anywhere, making it lighter and cheaper at the expence of lower reliability due to wear in the brushes.
 
ukrainian said:
Before - 12.2V, after - 14V.
Click to expand...

Are you sure that your battery is OK? 12.2 to 14v with just a blip of the throttle! I would get the battery tested first - you can't do that with a DVM.

RAB
 
ukrainian said:
Yep, I am thinking along the lines of regulator+brushes assembly., too. But I also came across this thread and began to wonder if it could be relevant. It seems alternator clutch pulley is TDI only, for 1.4 petrol we have an 'alternator freewheel clutch'. Perhaps they don't always fail noisily.
https://www.a2oc.net/community/index.php?threads/problems-diagnosing-alternator-failure.25566/
Click to expand...

I suspect the alternator clutch and freewheel clutch are exactly the same thing, their purpose will be the same - to reduce unesscessary drag from the alternator.
 
RAB said:
Are you sure that your battery is OK?
Click to expand...
Pretty sure, though it will be in its twilight years/months. The jump from 12.2 to 14V was in alternator charging voltage (when idling). It's as if just after the car is started, the alternator isn't doing anything, but then is 'kicked into gear' by blipping the throttle. That's what makes me think it is a mechanical problem. Brushes barely touching the sliprings, or this clutch thingy not engaging properly at idle. I should know for sure tomorrow.
 
ukrainian said:
Pretty sure, though it will be in its twilight years/months. The jump from 12.2 to 14V was in alternator charging voltage (when idling). It's as if just after the car is started, the alternator isn't doing anything, but then is 'kicked into gear' by blipping the throttle. That's what makes me think it is a mechanical problem. Brushes barely touching the sliprings, or this clutch thingy not engaging properly at idle. I should know for sure tomorrow.
Click to expand...

If the voltage is erratic, it is likley to be the regulator.
 
So the car is back from the garage, with a brand new aftermarket alternator and no more lingering battery light. It would almost certainly have been the regulator brushes at fault. I could have carried out the repair myself for a fraction of the cost but I ran out of time.. My friendly mechanic said that the old alternator was the original Audi fitted part but was only a 90 Amp unit which is unusually low for a car with aircon and heated seats. So that may explain why it started to fail at 57k miles.. or perhaps it's the way I drive it :D
 
A bit late now but out of interest the alternator rating for the car is one of the items normally specified in the option codes (decode sticker in boot or handbook). At first glance the 90 amp is correct for a 1.4 petrol but there is more information in a helpful post here by Robin_Cox.

Andy
 
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