Dim battery light before ignition, then flickering

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Dim battery light before ignition, then flickering

Post by andycadabra » Tue Aug 23, 2016 9:35 pm

For the last 3 weeks I've had a flickering battery light (at first it would go off after a while), but strangely no starting issues as yet (powerpack in boot ready). I've had two alternators fail in the last 2 years, so I'm getting used to that, but if the alternator's failed the battery light is supposed to dim when the headlights are turned on, and it doesn't seem to be affected. the battery is registering 11.9 V before the engine started, and 11.6 V after.

The key clue might be that the battery light is only lighting dimly when the ignition is first turned on, when it and all other warning lights are supposed to be fully on prior to the engine starting, after which they generally go out.

Any ideas, anyone?
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Re: Dim battery light before ignition, then flickering

Post by rutter123 » Wed Aug 24, 2016 11:41 am

Put a volt meter across the battery terminals with the engine running to see if its charging, anything above 14v is ok, that will rule out the alternator being duff.
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Re: Dim battery light before ignition, then flickering

Post by andycadabra » Wed Aug 24, 2016 12:44 pm

Hi rutter123. As I mentioned, the battery is registering 11.9 V before the engine started, and 11.6 V after, so not charging, though I'm surprised its lasted 3 weeks like that.
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Re: Dim battery light before ignition, then flickering

Post by rutter123 » Wed Aug 24, 2016 3:53 pm

Bad alternator i suspect then, may well be worth checking the battery terminals if they are the originals they could be suspect moreso the positive one. they can break down internally ive had this happen myself, i now use marine type battery terminals. Also check the wire from the alt back to the battery isn't broken at the lug alternator end. I f you find the alt is duff then get a pug 406 alt from ebay plenty on there for around 30/40 quid new will fit straight onto the bx brackets and is a much better unit rated at 80Amp even has the 5 rib pulley on it, i use these on my bx's.
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Re: Dim battery light before ignition, then flickering

Post by andycadabra » Thu Aug 25, 2016 3:26 am

Thanks for those tips rutter. Today I replaced the neutral battery terminal, to no avail. I presume the wire to check is the small one that goes to the tab connector on the alternator? On mine this is green and disappears into the wiring loom after about a foot.
I can't remember, but I think the battery light came on with all the other warning lights, before the engine is started. Is it any kind of clue that mine isn't, except very dimly?.

Any way of knowing it's definitely the alternator and not the Voltage regulator?
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Re: Dim battery light before ignition, then flickering

Post by ken newbold » Thu Aug 25, 2016 11:46 am

From my experiance, the alternator
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Re: Dim battery light before ignition, then flickering

Post by rutter123 » Thu Aug 25, 2016 7:41 pm

Could be either or...i would change the whole unit for a new one, best to be safe than sorry. you can put a voltmeter direct to the large terminal on the alt if you get less than 13v then its toast.
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Re: Dim battery light before ignition, then flickering

Post by mat_fenwick » Mon Aug 29, 2016 12:17 pm

The dim warning light suggests that either there is a high resistance in the ignition switched circuit on one side of the bulb (highly unlikely assuming everything else is at normal brightness); or a problem with the earthing of the bulb via the voltage regulator. I'v no idea whether an internal regulator fault could cause this, but it seems a rather large clue!

I would check the wiring for the warning light bulb (the thin wire to the alternator) as if this is high resistance, it will cause a dim bulb but not a lack of charging, although can do if completely failed.
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Re: Dim battery light before ignition, then flickering

Post by andycadabra » Wed Aug 31, 2016 5:10 pm

Thanks for those thoughts, Mat. There is bit of a pattern to the problem. The flickering battery light problem with apparent battery discharge, usually goes away after having driven about 3 or4 miles (i.e. the light goes out). Then when I turn the engine off, the battery light lights up as it should in the pre-ignition phase, and goes out once the engine is started. I measured the charging situation with the engine running last night and it registered a healthy 13.6 V.

However, starting it up today , the flickering light is back. With the engine running the battery voltage measures 12 V, and without the engine running 12.1v, so slowly discharging.

Does this suggest a bad connection somewhere, or some part of the circuit that only comes to life when the engine's reached a certain temperature, or can alternators/regulators behave like this I wonder?

the small green wire that goes to the tab connection on the alternator is on tight and after a few inches disappears into the wiring loom. I assume that as the battery is discharging when it's flickering, and charging when it's not, it's not a fault with the warning light.
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Re: Dim battery light before ignition, then flickering

Post by mat_fenwick » Wed Aug 31, 2016 9:57 pm

I must admit I missed the bit about flickering before, which would tend to suggest worn brushes. Never known that to cause a dim warning light with the engine off, but if the lamp is earthed via the brushes and slip ring (I think it is!), wear would increase the resistance and cause it to be dim.

http://www.jcrsupplies.co.uk/products/A ... UILD_PARTS

might be a useful link if you want to repair yourself.
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Re: Dim battery light before ignition, then flickering

Post by andycadabra » Thu Sep 01, 2016 9:37 pm

thanks mat - It had occurred to me that there must be something fundamentally wrong, possibly with the wiring since the problem is evident in the pre-ignition phase, before the engine is running, and your theory would fit in with this, so I tried to do some tests.
I disconnected the small wire from the tab on the alternator with the intention of connecting it to Earth to see if the battery warning light would light in the pre-ignition phase as it is supposed to, but when I tested it for voltage between it and my negative battery terminal it registered 12 V positive. Then, when I tested the voltage between the Connector on the alternator and the battery's positive terminal, the tab connector registered 12 V negative. These tests were in the pre- ignition phase btw.
All this has left me a bit confused since my primitive knowledge of electrics tells me that connecting a positive voltage with a negative one results in sparks and/or blown fuses!

Do you think an alternator with worn brushes would behave the way it is i.e. doing little until it's been driven about 4 miles and then working perfectly?
If so, I'll try and do the brushes, which can be bought on eBay apparently for £3.25 including postage.
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Re: Dim battery light before ignition, then flickering

Post by mat_fenwick » Thu Sep 01, 2016 11:05 pm

Your measurements are exactly what I'd expect - the alternator terminal is 12 volts below battery voltage (i.e. earth), and the reason the wire registers +12 volts is because negligible current is flowing when disconnected (only the tiny measurement current taken by the meter) hence no voltage drop across the bulb.

I suppose it's plausible that worn brushes could behave like this, but I've not seen it. The only time I've ha brushes fail it's been a flickering light which started at low revs, and gradually became permanently lit at all revs.
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Re: Dim battery light before ignition, then flickering

Post by electrokid » Fri Sep 02, 2016 10:27 am

Hi Andy,

It does sound as though your alternator is stuffed again ! I get the impression that remanufacturing only involves fixing the one thing that has failed rather than replacing everything that could be worn. Although a remanufactured alternator should be fully working I think there will be components which are pretty worn with the chance that they won't last anywhere near as long as a new unit.

eBay has some...

http://www.ebay.co.uk/sch/i.html?_from= ... c=1&_sop=7

the cheapest and nearest with 100% feedback priced at £36.48 and £55.00 and one in Doncaster at £44.99
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Re: Dim battery light before ignition, then flickering

Post by andycadabra » Fri Sep 02, 2016 12:18 pm

Brian - The re-manufactured one I bought from Mister auto 2 years ago failed within 10 months, but I managed to get most of my money back from Mister auto. Replaced it with a second-hand Bosch, which has been fine until recently.
Rutter recommended getting a Peugeot 406 one and a 'lowest price first' search on eBay brought this one up which looks like it'll fit. At £14.99 I snapped it up but if there's any reason why it might not fit please let me know quickly.
Seemed like the best way to go ...If the problem is something else, at least I'll have an alternator to sell on eBay! Thanks everyone for your help
http://www.ebay.co.uk/itm/162081758295
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Re: Dim battery light before ignition, then flickering

Post by KevR » Fri Sep 02, 2016 12:59 pm

With the engine running (and not charging), give the alternator a sharp smack with the business end of a big stick. If it starts charging then the problem is almost certainly worn slip rings and/or brushes, or even just a build-up of crud. I've used them for months on end like this, just givin them a whack when needed! Eventually whacking it won't work though, so better to sort it out properly. Slip rings and brushes are cheap enough, but I'd be inclined to go down the 406 80A route as suggested above.
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