Battery light on after refitting..

[Damo15]

On friday night i left the in car light on overnight by mistake, came to it next morning and surprise surprise, it was dead.. I borrowed a booster to jump it, drove about 4 miles to charge it up and when i got back home i turned the engine off, went to turn it on again and it was still dead. So cause i had thing to do i swapped the battery from my old car. The battery light came on, but i assumed it was because the other battery was slightly less powerful. Ive charged the flat battery up and refitted it today. But the battery light is still on? Ive tested it with a meter and the readings telling me its charging. Any ideas as what to might be the problem?

Any help is much appreciated.

Thanks.

[Breezy_Pete]

4 miles wasn't really enough to put any significant charge into a dead-flat battery.

What were the readings that led you to conclude the charging is all hunky-dory?

[Damo15]

I got 12.5 or 6 when it was off, and 13.7 with engine on.

[Breezy_Pete]

14.2 would be a much better number to see when running, but I doubt that 13.7 is low enough to bring the warning light on without something else wrong.

 

I would say that it might be alternator brushes worn too far down, or a bad contact to the voltage regulator, but it's odd that this has coincided with the flat battery incident.  No sign of the battery light before? (Other than at ignition on).

[Damo15]

Yea i read it should be in the 14's but at 13.7 i thought well its doing something..

Well that was my thoughts, it could be the alternator, but everything was fine before i flatterned the battery. The light has never come on before. Unless it is just perfect timing lol.. Ive looked at the connections on both battery and alternator. Nothing obvious. So im stuck as to what to try next.

[Breezy_Pete]

Depending on which engine your car has, it's either awkward or very awkward to reach, but have a go at cleaning up the earth cable to the starter motor, where it bolts onto the upper mounting stud.  That gained me a few tenths of a volt on my Polo, after I found that there was a significant drop between alternator body and battery negative, and narrowed it down to that connection. 

 

To check whether this is worth doing, stick a few current users on (engine running), e.g. headlights and cabin fan on a high setting, then measure volts between a cleaned-up bit of alternator case surface and the battery negative post.  I found about 0.6V drop, and by moving the probes step by step towards each other, found that that was mostly happening at that one connection.

[Damo15]

Its the 1.4 mpi engine.

Ok will try this tomorrow. Hopefully i can narrow down the cause. Thanks for the help, will report back tomorrow with my findings.

[Damo15]

Not had chance to test for faulty earth.. The car died on me, lights and power steering went. Got it home,.and it was flat again.. So the alternators not charging.. Taking it to a local car leccy to see if it can be repaired or if need a new one.. Hopefully not the latter.. Only had the car 2 weeks..

[vindaloo]

if you're taking to a place, take your multimeter with you. Do before and after checks of the battery voltage, with the car off and with it running.

 

Might be worth check for the alternator load sense wire problem.

 

http://www.briskoda.net/forums/topic/334979-alternator-load-signal-wire/

http://www.seatcupra.net/forums/showthread.php?t=209472

 

J.

[rum4mo]

If it is not the wiring as above, I'd reckon that you did a "rough" jump start and that annoyed the alternator's built in regulator pack, there used to be surge protection diode that failed on alternators, but nowadays it is all sealed in as one unit, so if faulty that regulator pack needs replacing, or maybe cheaper and more effective at a higher mileage to get a properly reconditioned alternator.

[Damo15]

Ok, so while i was at work my father in law took the alternator to the local car leccy, tested it, was only puttin out 10v. They replaced a part, and now its puttin out 14v. The part though, i dont know what it was, the in law forgotten what it was.. Helpful. Anyway, he refitted the alternator to the car. Said it works fine now, no lights, no problems. So after work i went to pick it up... Dead.. So luckily, it had the battery from the old car in, and i replaced it with the original battery which was charged. Started fine, no lights. Hunky dory, go to start it again 2 hours later, starts fine, but battery light came on

Soon as i hit the revs, it went out. Tried again another 3 hours later, same thing.. Come to start it this morning, and low and behold... DEAD... Somethings draining the battery. But what!!??

[rum4mo]

Well sod that!  I'd think that the lesser of your issues is the battery light staying on until you raise the revs, that could be down to a wiring fault under the car, but what your main problem is - ??? as no one so far has reported these broken wires shorting out and causing a battery drain.

[giandougl]

If the battery was sound to begin with, an overnight drain from the interior light shouldn't drain battery dead..

Double check battery with tester, then take it from there.

PS: you get no real warning when battery dies, it's like it's having a heart-attack..zonkl!!!! goodniht Vienna.. LOL

[Damo15]

Found the culprate... A stuck relay, suspect maybe from the in car light i left on? As there have been no problems til then. So touch wood, problem solved. Hopefully tomorrow the battery has survived its recent heart attacks and is still alive lol.

Thanks again for all your input

[VWD]

Best test for alternator is to test under full max load car can offer to system -full lights/heater/radio/screen heater etc .Voltage should then be around the mid 14's.

[VWD]

Damo - glad you like my suggestion. i've always been taught that for electronic/electric kit, there are two extremes to test to .

1)- voltage regulation on no load.

2) Voltage output regulation on full max load.

 

Anything else is a function of the two extremes. At no load, the regulation should keep the output within limits, and thre should be sufficient reserve to ensure that at max loading, the output is maintained.