battery light on permanantly?

[Ralf85]

Vehicle electrics never cease to confuse me, but one of our electrickery experts should post up soon to help!

[California Dreamin]

Test actual output on the back of the alternator (large spade connectors in the black plastic block or 8mm post on later 65ah & 90ah units) be careful not to short. You should be seeing 13.8 - 14.5volts with the engine running. Is the small blue wire connected to the rear of the alternator? this is the exciter feed, without it the alternator won't charge.
Other things to look at are: earth leads, especially those in the engine bay....
If after checking the above you still don't get a 'raised' charge output at the alternator, then you may have a more fundamental issue with the alternator diode pack (the unit that changes useless alternating current into the direct current needed to charge a car battery.

Martin

[MidLifeCrisis]

Would the relay affect the actual charging though or just the light. It's definitely not charging.

There's no relay involved in the battery light circuit so the problem is probably elsewhere.
If you say that it is 'definitely not charging' - then the problem can only be either the alternator or the wiring to the alternator.
Are you saying that there is no increase in voltage at the battery when the engine is started?
Have you tried measuring the voltage at the alternator?

[Ralf85]

[quote="MidLifeCrisis
There's no relay involved in the battery light circuit... [/quote]

That's really helpful. So what's the click that definitely happens just as my battery light goes out?

[California Dreamin]

The clicking is probably the Split charge relay connecting your starter battery to your leisure battery....Which wouldn't normally work if it wasn't receiving a feed from the alternators exciter circuit....by this I mean, it indicates that higher charging voltage is occurring...a bit of a contradiction considering how you are describing the fault.
Do the charge check at the alternator....

Martin

[Ralf85]

That's really helpful. So in a westie that's clicking under my seat. Cheers!

[California Dreamin]

Yes.....handbrake side of the battery box on the drives side L/H/D....5 terminal split charge relay.
As a side note to your charging issue, it might be worth disconnecting the leisure battery terminals whilst carrying out your charging checks (make sure you insulate the terminals with rag or something else)

Martin

[AdrianC]

I don't know if this is the same issue, but my battery light stays on sometimes, until I rev the engine slightly. Then I hear a click and the light goes out. So possibly a sticking/knackered relay switch perhaps? I'm guessing the relay is on the back of the fuse box, but somebody else will know more than me.

If it's any consolation, ours does exactly the same, and charges just fine.

AIUI, the light is reporting on the split-charge, rather than the alternator's field excitation wire. The split-charge doesn't kick in until it sees proper charging voltage.

[Jayjaysee]

I'll do the charge check at the alternator as there is no charge voltage at the battery.

[Jayjaysee]

Ok. Finally got around to this and after wrestling the connector off the back of the alternator I couldn't get a voltage reading at all from the spade connectors.
The wiring to the connector itself is also exposed and looks like it's seen better days

I guess there are 3 options now

1) replace the alternator for a new one
2) take the alternator out and get someone to fix it
3) take it to a garage and say "fix that please mate"

Thanks for all your help guys

[kevtherev]

take it to an alternator/startermotor reconditioner.
they'll do it while you wait.

[Jayjaysee]

Just thinking about this again and there are 3 connectors on the alternator. One for the exciter cable and the other 2 for charging. Unless I'm wrong. Which 2 should I be taking the voltage reading from?

[Oldiebut goodie]

Earth and one of the big ones. You shouldn't see any voltage across any of those terminals alone in any combination. You won't get any voltage output without putting a voltage on to the exciter terminal. Leave it plugged in and flip up the covering to the terminals.

[Jayjaysee]

Oops. That's right. I didn't see any reading across any terminal without the cable plugged in. So I removed and called the alternator man

Looks like it may have been the cable then after all. Well I've ordered a new connector block now and the alternator man can give it the once over anyway

[California Dreamin]

When we say 'check output at the alternator' this means, WITH everything connected...otherwise how could it work?

Understanding that the alternator simply turns the kinetic energy of rotational movement into electrical output with the addition of a small current that 'excites' (creates an electro magnet) in the rotor windings. It is by varying the STRENGTH of this electro magnet that the 'OUTPUT' of the alternator is controlled.

In simple terms.....has the alternator got a 12volt feed on the blue exciter wire (ignition on). Has it got a good earth? is the belt driving the alternator tensioned and not slipping? then putting your voltmeter between one of the large spade connectors (everything still plugged in) and an earth, you should see an output of around 14 volts...please report your findings.

Martin