Help - red battery dash light

[Jim D]

Please help! (i'll give the full story hoping it will help with diognostics)
recently the red battery dash light appeared in my van as i was leaving work. worried by this i quickly stopped to investigate.

i pulled over, and it turns out i'd left my side lights on all day at work. The van didn't have an issue starting so it didn't occur to me at the time. anyway, noticing this, i switched off the lights and the dash light went out, phew. but to test, I switched them back on again and the dash light once again appeared. stupidly i did this a couple of time to check (clearly too many) because even after turning off the lights the dash light remained on. i figured at that time, perhaps this light was to do with the charge of the battery (as i'd left my lights on) so thought it would go out once i started moving and charging the battery.

I got down the road and it didn't go out, more worried at this time, i pulled over again to look on the internet. after a few minutes investigation (on places like this) i'd read that it could be the alternator and possibly a couple of common problems.

Firstly the belt. so i went round the back, opened the flap hoping it was something nice and simple like this, i also have a spare in the van at all times. the belt was intact and looking fine though.

The next common problem could be the brushes on the voltage regulator. so hoping that a £20 regulator would be better than a costly new alternator, i took out the alternator and removed the voltage regulator, the brushes seemed ok, but it was my first time ever seeing them, so i ordered a new one using the part number. Once the new one arrived, i could see that the brushes were indeed worn so i joyfully put it all back together, put the alternator in the van and went to start the van fully expecting the light to have disappeared.

The light remained on.

i've tested the voltage on the battery which measured something like 11.78 (roughly as i can't quite remember) both when the van was running and not.

Does this mean that my alternaor has packed up. It was fine on the way into work that morning.
could it be because i left the lights on.
are there any other tests i can do
is it worth buying a second hand one.
could i have put the brushes in the wrong way.
is it worth taking the battery out and fully charge it.

The current alternator in the van is a bosch - 028 903 025 H - 70A

i welcome all comments and advice

Thanks

James

[Ralf85]

That is close to a dead battery. Leaving the lights on all day could discharge an ailing battery.
1) How old is the battery?
2) Have you fully re-charged the battery at home?
3) Have you checked the voltage across the battery with the engine running to see if the alternator is charging properly?
4) What is the reading?

[Oldiebut goodie]

3) Have you checked the voltage across the battery with the engine running to see if the alternator is charging properly?
4) What is the reading?

Yes!
11.78v!

Try putting a wire from the battery to the blue wire to the alternator and see if the alternator voltage output rises. (Rules out problems from the dash to alternator, although it is very low current and voltage that is needed to kickstart the alternator)
If it doesn't it looks more like the alternator isn't charging at all. You have changed the brushes which is the first thing that is usually needed.
Check that the thick positive/s from the alternator to battery are in good nick/present.

[Ralf85]

[quote="Oldiebut goodie
Yes!
11.78v! [/quote]
Silly me. I misread that bit of the sentence. So it looks like a new alternator is needed, but make sure you take the new regulator pack out before disposing of it and keep it as a spare!

[Oldiebut goodie]

Having lost 1/2v myself in that foot or so of cable from the alternator to the battery I would rule that out as a cause first though. Also the earth as it is more exposed than in a up front battery. Then it is looking more likely that the alternator is kaput. Alternator voltage at the terminal needs checking.

[MidLifeCrisis]

I'd try putting a known good battery in (from another car that you know works fine) and see what difference that makes - it would seem that your alternator isn't charging but given that the one thing you know you did is leave the sidelights on (which would discharge the battery) then I'd start there!

[bernard1973]

You need to check that the alternator is charging the battery - this is exactly what happened to my van.
Get a multimeter (set to 20V) and put the positive lead to the positive coming out of the alternator and the negative of the multimeter to the negative of the battery. Mine was goosed and showed 11.3V. It should be 13.8V up to just over 14v (any higher and it's not good and will fry your battery).

I've just changed the alternator and it's 13.84V now.

[edoh]

just for clarity's sake -
should that be -
positive post on battery to red/positive on multimeter
negative post on battery to black/negative on multimeter
battery fully charged /
multimeter set on 20v /
ignition on - should read - 12+v for a charged battery
engine running - should read 13.5 to 14.5v if alternator is working ok?
a la -
https://www.youtube.com/watch?v=dq24oPUVmdA" onclick="window.open(this.href);return false;

[Oldiebut goodie]

Better to measure at the alternator to rule out wiring.

[edoh]

good hint

[bernard1973]

Better to measure at the alternator to rule out wiring.

Yep. this is what I did. You can put the negative of the multimeter to the metal of the van, or the negative of the battery, but the positive of the multimeter goes to the positive of the alternator.

[edoh]

would that be where the blue wire goes?

[bernard1973]

would that be where the blue wire goes?

Not sure, but it's the wire that goes from the alternator to the positive of the battery. I put the multimeter to the nut that attaches the wire to the alternator.

[edoh]

thanks so much - all good to know

[ghost123uk]

The blue wire goes to the dash. It is an important bit of the red charging light circuit. In addition, it is also very often used to activate the leisure battery split charge relay.