TD5 - Red Battery Light Stays On, Despite New Battery Being Fitted and Running Well!

paul_c said:

If the battery light doesn't go out when engine running, you can be 95% certain its a faulty alternator. To be 99.99% sure, take it to an auto electrician who can do a 'spin test' of the alternator, ie he tests it off the vehicle. He'll probably also be able to rebuild it at a lower cost than a replacement alternator. By all means, you could buy one off a scrappy etc, but there's no guarantee of its longevity.

A check of the relevant fuse(s) is always worth doing anyway, since its quick and easy.

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Hi Paul

Thanks for the replies...

I think we're 99% certain that the altenator is indeed kaput. The fuses have all been checked, and whilst one did happen to be blown, it wasn't for the alternator in any case, and after replacement, made no difference.

The key problem is:

LR Main Dealer - £400 for a Denso OEM part

LR Breaker in Scotland - £35 (+postage of £10) - bought with the protection of Paypal in case its a duffer when it gets here.

The warranty on the new part is only 1 year - I'd have to get through more than 11 used ones to break even! It's a no brainer for me....

Don't you have any local auto electricians?

For the time / effort in taking the little monkey out (est 2 hours because of its location) - I don't want to spend time on fixing something that's likely to be broken. It makes more sense to just have the replacement fitted at the same time, and then think about refurbing the one that came out.... otherwise the mechanic bill just gets bigger and bigger, and my wife is car-less for longer.

Sadly - the alternator was kaput.

Got a good used one on Ebay, and got it fitted - job done for about £50 all in, so can't grumble too much at that.

Anyone looking for a cheap and very reliable local (mobile) mechanic in the Canterbury area - drop me a line, I've found a gem!

rjsdavis said:

Ok - checked all of the fuses. Found that was blown in the engine bay, but this related to the headlamp washers.

F24 was fine, as were all of the other fuses underneath the steering wheel. Then tried a voltmeter on the battery....

With everything off, the voltmeter registered a steady 12.9V. When the engine was running, this dropped to 11.95V and again was steady. I'm assuming that the alternator is defo dead, and probably died trying to charge the old battery that was mullered too?

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What should the alternator output be?? I checked my one yesterday with a warm engine and 2k rpm and was getting 13.35v across the battery

Something like this : 12v then 14v with the engine running.

I may have an alternator or regulator on its way out?

DISCO2RS4 said:

I may have an alternator or regulator on its way out?

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Not necessarily, even my £220 Fluke meter which I have certified every year is out by + 2% so don't worry, unless you are having electrical issues. I use my Anolog meter on vehicle batteries and wiring normally, much more stable/accurate. Digital is for electronic products.

Does the 13v stay when all your electrical items are on at once. ? If so the alternator is coping.

Perfect, sounds good to me.

IMO nothing is good below 13.5 with loads on, especially at 2000rpm, it's possible that a diode to be shot within the diode pack then beside the low voltage/power there is an ''unhealthy'' sine wave component too in the supply and a parasitic drain.... unfortunately that's verifiable only with oscilloscope

Thanks sierrafery, are these diode packs changeable? that test I mentioned above was with no load at all :/

Yes they are http://www.ebay.com/itm/ART109-Dens...r-Defender-Discovery-II-2-5-Td5-/261745381619 but if there was no load it can be the regulator too http://www.ebay.fr/itm/DEFENDER-DIS...6-ALTERNATOR-REGULATOR-BRUSHBOX-/291558181767 ... investigation is needed before you replace parts

Thanks sierrafery, what test do you recommend next? warm it up and put all lights, radio etc on and see what the alternator pushes out? I also have the chain tensioner seal/washer leaking right onto the alternator, would this have an affect on it?

Just take the car to Halfrauds - they will test it for £0

You could, of course read the "alternator testing" thread in the CFAQ section

DISCO2RS4 said:

Thanks sierrafery, what test do you recommend next? warm it up and put all lights, radio etc on and see what the alternator pushes out? I also have the chain tensioner seal/washer leaking right onto the alternator, would this have an affect on it?

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no fluid ingress into an alternator would be a good thing ever... you dont have to warm up anything, from cold start at idle the voltage should grow to 14+ in max 30 seconds then if you switch on all the heavy loads it can drop below 13 but must start to rise to above 13.5 on it's own and if you rev it above 2000 it must get close to 14 again... that's how a ''healthy'' alternator should behave... the gist is that it should not stay below 13.5 what ever you do