battery light on??

goony · Post by **goony** » Sat Nov 25, 2006 4:44 pm

Hi guys on monday morning whilst driving to farnborough the car got a real soaking and now the battery light comes on below 2000rpm any ideas why???
im going to give the altenator a good soaking with WD40 tommorow to see if that helps what do you think??

goony

jeremy · Post by **jeremy** » Sat Nov 25, 2006 5:17 pm

Is the belt tight and in good condition?

Check the voltage. Proper figures are given in Haynes but when its running after a few minutes the voltage across the battery whould be 14 - 14.4 volts. If its around 11 then one of the alternator phases has failed.

After the car has been standing overnight, and before the car is started the voltage should be 12.5 for an sound battery, 12.6 for a good one and 12.4 for a poor one. Again if its substantially below that an alternator ohase isn't working. (it will be 10 or 11)

WD40 is an insulator and in the short term a lubricant. I would have thought that conducted heat from the engine would have dried out any moisture by now.

ken newbold · Post by **ken newbold** » Sat Nov 25, 2006 6:04 pm

Heavy rain = lights on, wipers on, fan on, not to mention heated rear window.

New or recond alternator me thinks.

goony · Post by **goony** » Sat Nov 25, 2006 6:30 pm

the light comes on even with everything turned off

goony

ken newbold · Post by **ken newbold** » Sat Nov 25, 2006 6:55 pm

Mmm it will, your atlernator probably needs new brushes.

RobC · Post by **RobC** » Mon Nov 27, 2006 4:06 pm

what about if the battery light doesn't light when you turn the ignition on? Is it simply a bulb gone in the instrument panel or does it mean something?

ta

tim leech · Post by **tim leech** » Mon Nov 27, 2006 4:26 pm

My 16v does that and ive changed the bulb to no avail!

jeremy · Post by **jeremy** » Mon Nov 27, 2006 4:33 pm

The light is actually an integral part of the system, and its failure may cause poor charging.

Is it connected to the alternator? Is the wire intact? Is the circuit on that back of the instrument panel sound? Are its connectors on properly?

Post by **docchevron** » Mon Nov 27, 2006 4:38 pm

The alternator cant charge if the light doesn't work, the light is lit by a ignition fed supply to one side of the bulb, the other side of the bulb is connected to the alternator and goes out because when the the alternator is "excited" it provides a + supply to the bulb, hence when it's charging the bulb has + voltage on either side of the circuit and the bulb is extinguished.

If the bulb is U/S or the ignition fed supply to the bulb is U/S then the alternator doesn't know whether to charge or not.

Cheers
Chris G

tim leech · Post by **tim leech** » Mon Nov 27, 2006 4:46 pm

Mine dont work but im sure the alternator charges ok as the battery dont go flat? Well it hasnt yet!

Vanny · Post by **Vanny** » Tue Nov 28, 2006 12:47 am

good money says that every time you og out time, you do over 10 miles? I have the problem where the battery light never comes on, the bulb however is fine, for the most part i dont have any starting problems, but i have to have the blowers where ever i go (blown head gasket) and a couple of night time drives of under 5 miles means i end up with a dead battery! The problem is that as Doc describes if the wire from the battery light to the alternator isnt there or working then the alternator armature isnt properly initialised. THe amount of charge the alternator puts out is related to the initial voltage it is provided through the armature wire ie the lead form the battery out bulb!

I know this as theory (AC power transformers and transmission) but also that if it wiggle all the wires and pull apart the connectors and reattach sometimes the battery light will come on with the ignition on the first click!

All that needs proving is for the wire to be replaced!

In the case where the battery light stays on all the time (i've had that too a couple of times) it was down to a drain on the circuit due to faulty wiring, i've had this caused by a dodgy earth strap to the engine, a stuffed starter motor and a really screwed relay, also on occasion by a dodgy old alarm!

I know of many land rover defenders where when you start the car the battery light stays on until you go over 2000rpm then goes out for the rest of the journey. I'm told in this case that it is likely due to worn bushes sticking in there tracks.

goony · Post by **goony** » Fri Dec 01, 2006 5:51 pm

well it got worse over the last week and last night needed 4,000rpm to put the light out. when i left farnborough to go home to peterborough i stopped for diesel and it wouldnt turn over again!!!!

quick call to the RAC and a very nice man turned up after about 15 mins
and helped push it off the forecourt then he jumped started it and got the volt meter out and sure enough the altenator wernt working! BUGGER
he could see that the alternator was newish so should work ok and i explained to him about the soaking it got and he went AH hang on a moment and got a big socket extension and gave it a few taps and hey presto the volts shot up
turns out that if it gets really wet then the dust from the brushes turns to a thick paste and stops the brushes from sliding forward as they wear out and so it creates less and less charge and a few taps is enough to free the baked in crust of paste and let it make contact again and now its as good as new

goony

tom · Post by **tom** » Sat Dec 02, 2006 10:04 am

So far. I'd suggest that you take the black box off the back of the alternator and give it a good clean up with hot and soapy before drying it off. Don't go near it with WD40 under any circumstance.