Battery Warning Light - LR 90 V8

Hello everyone,
the battery warning light on my 90's dash always turns on when I start it but turns off almost immediately afterwards. Well, it did. Now it just stays
on, its brightness varying: - It's always on but very dim. Rev the engine over a point and it goes erratic, continuously turning brighter, then dimmer. I'm assuming it has to do with the spark plugs although I'm not sure (the frequency seems a bit irregular/unstable) - Use anything that needs electricity and it goes proportionately brighter - accordingly, the battery voltage gauge drops to a bit below the middle mark with the headlights on.
It's been like this for months without any problem to the vehicle's function and it always starts with half a turn of the key. I don't remember the exact values any more but I checked the voltage on the battery and it seems to be fine with the engine off and charging properly (revving increases the voltage up to a point) when running. The battery's own indicator suggests it's ok. I put it on a CTEK charger a couple of times and it charged without any issues.
So what say the wiser owners? What would cause the battery check to state there's a problem when there doesn't appear to be one?
--
Geo


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Geo wrote:

Typical of a clapped out alternator. Probably worn brushes in the alternator. Possibly a defective rectifier diode in the alternator. Possibly the regulator. The cheapest repair is normally an exchange alternator, and check the wiring before you fit the new one.

The battery check is showing a problem because the alternator isn't putting out enough current to keep the battery fully charged.
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"John Williamson" wrote

I thought about the alternator but I've been using the vehicle like that for six months now (half of the time with the lights on) and I don't see any evidence of a weakening battery. Perhaps there's still enough current to fully cover my needs but not as much as a healthy alternator would produce? Given that replacing the alternator isn't the cheapest of options and I haven't been left stranded yet, I'll leave it until I get the vehicle serviced in a month or two... or until I am left stranded.
Thank you for your answer.
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Geo


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ays

Long time since I've been on this fine group, but I agree that it's a knack ered alternator - mine did the same for quite a while while the battery ver y slowly went down (over many weeks), it died when we finally got to winter . If you're not totally reliant then I'd stick with it and just keep a wea ther eye on the battery, and perhaps keep a watch on the forums for a repla cement.
Bob
1990 ex-RAF 110 3.5 V8 17KJ83 1967 3/4 ton Sankey 09ES17
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Bob's not wrong, but if you just leave it alone, you _will_ kill the battery. I'd top it up regularly, say once a week, with a charger. They should be kept fully charged otherwise the battery degrades quite fast.
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SimonM

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"SpamTrapSeeSig" wrote

Bugger, I was hoping I'd get away with some easy (read: cheap) fix. I suppose I'll have to schedule a replacement within reasonable time, in the meantime I'll keep an eye on the battery and use my charger once in a while. I guess 25 years and 125000 kms of service isn't too shabby for an alternator...
Once again, thank you all for the answers.
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Geo


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snipped-for-privacy@hotmail.com says...

<Snipped>
What age 90? Do you know what make/model of alternator is fitted, some are *Much* easier to DIY fix than others. (The old Lucas ACR series in particular are easy to fix.)
If the brushes are worn, don't leave it too long, or the slip rings too will be damaged, and that can write off the whole thing. Unless you have a stock of similar machines to canabalise.
Check too, for chafed wires relating to the warning light, loose terminals and so on. TAKE CARE!!!! It is best to disconnect the battery (-ve side) so if you short something by accident, you don't start a fire and burn out your wiring loom.
If your 90 has any security gadgets, make sure you know the unlock code (s) Same for the stereo etc (If you have that luxury!)
Using a good voltmeter (Digital preferably) measure the battery voltage with the engine off (after an hour say.) It should be at least 12.4V Much less than that, and either the battery is low, or on the way out.
Start up, and after a few minutes to recharge (give it the chance to replenish the grunt needed to start the mill) it should be up to some 14V. Turn on the headlights, and anything else beefy you might have (heated windows etc) the battery volts should stay at much the same with the engine running, even at idle. (They might drop a little, plus a hard working alternator at idle speed can make a bit of a whistle. If it realy screams at you, you might have lost one winding/phase/diode etc.)
Poke arround locally for a Truck Electrical specialist. Often, they can repair alternators for very economic rates, usually for much less than an exchange unit, unless something major has failed "big time". Even then, they probably have something suitable at reasonable cost. (Truck firms like low costs, and they dont like short term repairs either!)
The tiddly little things on LR's will be no problem for them. I've had bearings replaced and all sorts over the years by one group in the UK, always good service (fast and cheap!) And the repairs stay good too.
They also do starter and winch motors too....
Have Fun.
Dave B.
PS:    Re ACR series alternators. They use the same bearings as Armstrong MT series bike front wheels. But, the bearings on the bike are sealed, those in the alteranator are not. Guess what I did one time for someone, and that is still working despite several dunkings in mudruns etc... :)
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On or around Thu, 9 May 2013 22:50:06 +0300, "Geo"

The altenrator is semi-shagged. I did once know what causes this one, I think it's one or more diodes in the rectifier going tits-up but don't quote me...
I had one like this and as you say, it worked fine although eventually it got worse. Chances are the output is just a bit low, which, in most use scenarios, doesn't show. If you did a lot of short journeys in winter, it might show as a gradual loss of charge.
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