battery warning light on but alternator charging fine

From CEM to VEM, from LED to lightbulb and more. If you have an electrical problem, like a broken info-centre, search for answers in this category. This is also the place to be when you expect the problem to be of an electrical nature...

Moderators: jifflemon, coyote1980, Rachel

Post Reply
Ade
Can tell where the 480 was built
Posts: 337
Joined: Tue Feb 28, 2012 3:25 pm
Location: Northants

battery warning light on but alternator charging fine

Post by Ade » Wed May 23, 2012 3:50 pm

Hi,
My battery warning light has come on but when i tested the alternator it seems to be charging fine and the car has been like it for a couple of days now and its still going strong. I have changed the voltage regulator not that long ago and only managed to obtain some shitty no-name one and wondered whether this might be causing it. I have have studied the wiring diagrams and it appears that the warning light earths to the regulator so is it the regulator thats responsible for 'deciding' whether there is a charging current or not and therefore allowing the light to earth (or not). By the way, the voltage regulation is fine, just wondered whether another aspect of my 'high quality' :badmood: regulator has gone a bollock and is allowing the light circuit to earth even though there is plenty of charging current.

Thanks in advance,

Adey
O.C. 480 D.

Espada
Started learning about 480
Posts: 64
Joined: Wed May 23, 2012 6:43 pm

Re: battery warning light on but alternator charging fine

Post by Espada » Wed May 23, 2012 7:26 pm

Not 100% familiar with 480 charging but wiring diagram looks normal so turning on ignition sends +ve along the small red brown cable from charging light to the alternator. Now if the general circuit is normal starting the car also sends +ve back along the cable from the alternator and extinguishes the warning lamp. The other purpose of the warning lamp circuit is to excite the alternator, if this fails then there is a good chance that the alternator will not charge but yours does. However the alternator can still spring to life if the engine is revved and I notice the diagram shows a small resistor so is it possible that this is how you are still maintaing a charge. Although this will not prove your regulator it might eliminate some of the faults. Turn on the ignition but dont start the car I presume the charge light is on, on the alternator remove the small red brown cable has the light extinguished? If yes it might suggest that the alternator is not sending the power out of this connection to extinuish the lamp so re check everthing at the alternator end. If its still on the its definately not the alternator at fault. Hopefully failures in voltage regulators would show up as very bright bulbs etc im guessing so if lucky bad connections at the alternator end.

themaster
480 Newbie
Posts: 39
Joined: Wed May 11, 2011 9:39 pm
Location: Bristol, UK

Re: battery warning light on but alternator charging fine

Post by themaster » Wed May 23, 2012 9:08 pm

I kind of had that, where the battery light came on. I bought a new alternator (because that's what the light tells you to do) and subsequently found the old one was fine. A wire had broken between the alternator and the battery I believe.

If you're battery is decent, it can take several days to discharge and cause bad symptoms. What does the volt meter say? If it's charging then it ain't that... and that's where my knowledge ends :)

Ade
Can tell where the 480 was built
Posts: 337
Joined: Tue Feb 28, 2012 3:25 pm
Location: Northants

Re: battery warning light on but alternator charging fine

Post by Ade » Thu May 24, 2012 1:46 pm

thanks for the quick replies, the voltmeter is saying that its charging at about 14-15 volts, which is about right. Also, i think the battery would have been knackered by now if it wasnt because i drive 60 miles a day to work and back, with day running lights, ecu, stereo etc it would have flatted by now.

The other weird thing i forgot to mention is that the light is dim when idling but gets brighter with an increase in engine revs????? Normally the other way round when an alternator is on its way out because if its about to go then it will only produce current at high speeds. Had the batt. warning on my peugeot a while ago and it was bright when on tickover and got dimmer as the engine revved, showing that it was producing a little more charge at higher speeds, then of course, it did finally go a bollock and i changed the alternator and all was well.

the light does disappear when i unplug the red/brown earth from the terminal on the voltage regulator, figured it would though, seeing as that's it's earth point. Thats why i ask if its the regulator that also acts as a switch for the earth to allow the light to come on if there is no charge present.
i.e. open circuit when charge is present, but when no charge some component within the regulator assembly allows the red/brown wire to earth thus illuminating the light. if the regulator does perform such a function then thats why i am thinking it could be at fault because like i said, it was a crappy cheap one. Sound reasonable or am i talking shite??

all wiring as far as i can see is ok. Bloody mystery electrical problems on these 480's!! :wall:
O.C. 480 D.

Espada
Started learning about 480
Posts: 64
Joined: Wed May 23, 2012 6:43 pm

Re: battery warning light on but alternator charging fine

Post by Espada » Thu May 24, 2012 6:13 pm

Thanks for confirming that you have verified charging at the battery, your comments re the charging light glowing might point to the battery not the alternator. When you turn on the ignition it sends +12ve through the warning light to the alternator and then to earth lighting the lamp. On starting the enging the alternator springs to life and puts +12ve back up the same cable the two supplies cancel each other out and the lamp goes out. So normally when you rev the engine the output from the alternator increases and as it reaches the same voltage as the battery the lamp dims and extinguishes, yours is working the other way. As you increase the engine revs the alternator output is increasing but greater than that of the battery hence the lamp gets brighter. The higher the voltage with respect to the battery voltage, the greater the voltage difference across the lamp, and the brighter it gets. Now I know nowt about batteries can bad connections add to this? I dont know, but I would definately look at getting the battery checked before going further. If you still have the Pug swap the battery over and see what it does.

Ade
Can tell where the 480 was built
Posts: 337
Joined: Tue Feb 28, 2012 3:25 pm
Location: Northants

Re: battery warning light on but alternator charging fine

Post by Ade » Fri May 25, 2012 7:33 am

Put a shiny new bosch s5 superduper battery on it not long ago (all 120 quids worth of it!! :shock: , so i doubt if its that. Thanks for clarifying about the voltages cancelling each other out, i understand much better how it works now, if you have the same voltage applied to a component but in opposite directions then the potential difference will be zero, got it! :D learn something new every day! More of a mechanical man myself, not a lot i can't do in that department being a mechanical engineer but electrics have never been my strong point.

I have noticed that the voltage regulation has gone a bit iffy contrary to what i said the other day. It was very hot yesterday and it seemed not to be charging so well (don't know whether it was the heat or just coincidence) but this morning on my way into work it was ok again, warning light still persistently there in varying degrees of brightness, but there's definitely some variability in the voltage, and putting even small loads on the system, i.e. fag lighter, blowers at low speed, seems to drop the voltage more than it should if the regulator was working properly. I know voltage regulators are not perfect and can only hold a line voltage up to a certain load before it starts to drop, but it should be good enough for a couple of amps, surely??

My instinct is still telling me to change the regulator and see what happens, its not that expensive so it's got to be worth a shot has it not. I have little faith in these cheap aftermarket components. I may be wrong but i think i'm gonna bite the bullet and do it for the sake of 20 quid and 10 mins, eliminates it as well if it isn't the fault.

Thanks for your help and i'll keep you posted about my findings after ive done a bit more investigating and quite possibly changed the regulator. Your guidance on the way the system works has been invaluable, many thanks, that gives me some ideas for tests i can carry out to try and get to the bottom of it.
will be looking at it tomorrow most likely. There goes a nice relaxing saturday blown to shit!! :badmood: I love volvo 480's, life just wouldn't be the same without one! The mrs will be so happy that i have to play with the car instead of her! :wife: :wink:

cheers,

Adey
O.C. 480 D.

Ade
Can tell where the 480 was built
Posts: 337
Joined: Tue Feb 28, 2012 3:25 pm
Location: Northants

Re: battery warning light on but alternator charging fine

Post by Ade » Fri May 25, 2012 7:36 am

Oh and yes, i do still have that hateful bag of shite 306, its been laid up for about 5 months and the battery had almost had it anyway so i doubt if it's gonna be much good now! horrible bloody thing!

306DTurbo :kill: headgaskets (repeatedly) :kill: :kill: :kill:
O.C. 480 D.

Espada
Started learning about 480
Posts: 64
Joined: Wed May 23, 2012 6:43 pm

Re: battery warning light on but alternator charging fine

Post by Espada » Fri May 25, 2012 6:42 pm

Will be interesting to hear how things go, as you say at 20 quid go for the regulator, It will eliminate it from the equasion.

At least its a nice sunny weekend you will be missing, have fun.

Regards

Simon

Ade
Can tell where the 480 was built
Posts: 337
Joined: Tue Feb 28, 2012 3:25 pm
Location: Northants

Re: battery warning light on but alternator charging fine

Post by Ade » Tue May 29, 2012 8:49 am

Hi all,

Problem solved!! :hopping: :hopping:

It wasn't the regulator after all (tried it with a scrap one, cost all of 2 quid of an old peugeot with the same alternator) :nuts:

I stripped the alternator down and tested the diodes in the rectifier, turns out one of the diodes was toast. There are 9 diodes inside the rectifier, two sets of three large ones for the positive and negative and a set of smaller ones for the warning lamp circuit. One of the large ones on the positive side was dead thus allowing more current and voltage to flow through the warning lamp trio, thus illuminating the light. This explains why the light was getting brighter as rotor speed increased too. Electricity will find the next path of least resistance which happened to be the warning light trio, yet the other two diodes that were still ok were allowing enough through to still charge the battery somewhat.
Quick trip in the old man's merc to Maplins for a couple of diodes (ended up having to put two 6A diodes in parallel, they didnt have any higher rated ones) and a bit of trickery later, one fully functional charging system!

A lesson worth learning from this is that when an alternator fails, it is rarely the rotor or the stator, it will be the regulator or the rectifier that goes a bollock. If you consider the cost of a new alternator against the cost of some new diodes and a regulator (all in about 30-35 quid), then as long as you have a working knowledge of electrics, it is quite feasible to rebuild the rectifier with new diodes for a fraction of the cost of a new unit. (not entirely straightforward as the stock diodes are pressed in at one end, but quite plausible if your a bit creative like me!)

The other thing you could do is completely bin the existing rectifier and purchase (from maplins or the like, rs components etc) a three phase bridge rectifier and wire it into the windings in the stator, secure the ends of the wires and mount the rectifier seperately (like they used to be), then simply put your positive dc to the battery and your negative dc to a good earth.

Hope this thread can diagnose future problems for people and give them a viable, far cheaper alternative to buying a whole new alternator.

So maybe my shitty cheap voltage regulator isn't so bad after all!! Still not a fan of cheap aftermarket manufacturers mind, I work as a design/prototype engineer for a company that buys its components from india and china (we used to make all our own stuff, but sadly costs became prohibitive, as is the way unfortunately) and let me tell you now, a bigger load of crap you will rarely see! bastards! :kill: :kill:

thanks for your guidance on the warning light system simon, added to that some further research and the problem was nailed!

Cheers,

Ade
O.C. 480 D.

Bong5
480 Newbie
Posts: 5
Joined: Sat Sep 22, 2007 11:26 am
Location: Southern part of Norway

Re: battery warning light on but alternator charging fine

Post by Bong5 » Fri Jun 01, 2012 3:07 pm

Cool.
Now I think I know what is wrong with mine.
This forum is more handy than any tool, book etc for my 480

480_rocket
480 Veteran
Posts: 799
Joined: Tue Jun 15, 2004 8:36 am
Location: Somerset, UK

Re: battery warning light on but alternator charging fine

Post by 480_rocket » Fri Jun 01, 2012 3:35 pm

I had same thing, dim at idle getting bright with revs. Car was fine for weeks as I thought it would be the regulator. Turns out it was something in the alternator (either diode or winding) but didn't go further as I just got a spare alternator from the scrap yard.

BTW, putting diodes in parallel isn't the best way, they won't be matched and one will probably take most of the load.
'92 480 Turbo, full leather and air con

Ade
Can tell where the 480 was built
Posts: 337
Joined: Tue Feb 28, 2012 3:25 pm
Location: Northants

Re: battery warning light on but alternator charging fine

Post by Ade » Fri Jul 06, 2012 9:16 am

I know what you mean, but it was all i could do and it's still ok so fingers crossed for the long run!
O.C. 480 D.

Ade
Can tell where the 480 was built
Posts: 337
Joined: Tue Feb 28, 2012 3:25 pm
Location: Northants

Re: battery warning light on but alternator charging fine

Post by Ade » Mon Jul 16, 2012 3:36 pm

The diode packs are in parallel anyway though?? :shock: :shock:
O.C. 480 D.

Espada
Started learning about 480
Posts: 64
Joined: Wed May 23, 2012 6:43 pm

Re: battery warning light on but alternator charging fine

Post by Espada » Mon Jul 16, 2012 6:59 pm

As you note they are already in parallel, I have never though looked into how they actually perform, do they act like resistors or capacitors in their calculations? time will tell but all looks good.

Basically congratulations in getting this matter nailed, unfortunately my broadband failed during the last post so I was unable to respond in a timely manner.

Next time I will try to not lead you in the wrong direction but thats all part of the fun.

Regards

User avatar
jamescarruthers
480 Is my middle name
Posts: 2501
Joined: Mon Jul 07, 2003 3:19 pm
Location: Cambridge

Re: battery warning light on but alternator charging fine

Post by jamescarruthers » Mon Nov 12, 2018 11:05 am

Thank God for this forum. I've just suffered this exact same problem yesterday with my re manufactured alternator‎ (I wanted to keep my original so had it reworked).

Noticed the battery light ‎was not illuminated with ignition and came on with the car started. I was quite far from home but was pleased to see that the lights didn't get dim nor the voltage go down as the drive progressed.

13.1V measured when charging (too low) which is thankfully enough, I hope, to keep me going for a few days until I can get this sorted. So not completely buggered but will need fixed ASAP.

Thanks Ade!‎
1987 Volvo 480 ES, 507274, 217 - Red (Ness)
2006 Citroen C6 Exclusive 3.0 petrol/LPG
2008 Mini Cooper convertible (Mau)

Previous 480's:
J123 CFU -- ES
J449 MNL -- ES auto
D864 CPV -- ES
L691 JFC -- Turbo
F70 MNR -- ES
H858 FGV -- Turbo auto
E981 KHM -- ES (509849)

jifflemon
480 Is my middle name
Posts: 2464
Joined: Sat Dec 17, 2016 11:03 am

Re: battery warning light on but alternator charging fine

Post by jifflemon » Mon Nov 12, 2018 12:06 pm

check it's not a blown dashbulb - Can happen!

As someone who used to repair them for a living (along with starters), I could bore you relentlessly about them.

However, even with a dead bulb you can get the alternator to self excite with a good hard rev.

User avatar
jamescarruthers
480 Is my middle name
Posts: 2501
Joined: Mon Jul 07, 2003 3:19 pm
Location: Cambridge

Re: battery warning light on but alternator charging fine

Post by jamescarruthers » Mon Nov 12, 2018 12:22 pm

jifflemon wrote:
Mon Nov 12, 2018 12:06 pm
check it's not a blown dashbulb - Can happen!

As someone who used to repair them for a living (along with starters), I could bore you relentlessly about them.

However, even with a dead bulb you can get the alternator to self excite with a good hard rev.
The light comes ON when the engine is running!
1987 Volvo 480 ES, 507274, 217 - Red (Ness)
2006 Citroen C6 Exclusive 3.0 petrol/LPG
2008 Mini Cooper convertible (Mau)

Previous 480's:
J123 CFU -- ES
J449 MNL -- ES auto
D864 CPV -- ES
L691 JFC -- Turbo
F70 MNR -- ES
H858 FGV -- Turbo auto
E981 KHM -- ES (509849)

jifflemon
480 Is my middle name
Posts: 2464
Joined: Sat Dec 17, 2016 11:03 am

Re: battery warning light on but alternator charging fine

Post by jifflemon » Mon Nov 12, 2018 12:56 pm

ah!

Rectifier buggered then! Is it a paris-rhone one? Bosch?

User avatar
jamescarruthers
480 Is my middle name
Posts: 2501
Joined: Mon Jul 07, 2003 3:19 pm
Location: Cambridge

Re: battery warning light on but alternator charging fine

Post by jamescarruthers » Mon Nov 12, 2018 1:02 pm

Paris Rhone. It is going back for rework. The diodes in the rectifier might have passed testing but actual heavy use has caused failure. They are the originals. Hope it can get me a few more days use! I'm visiting Jaster on Wednesday!
1987 Volvo 480 ES, 507274, 217 - Red (Ness)
2006 Citroen C6 Exclusive 3.0 petrol/LPG
2008 Mini Cooper convertible (Mau)

Previous 480's:
J123 CFU -- ES
J449 MNL -- ES auto
D864 CPV -- ES
L691 JFC -- Turbo
F70 MNR -- ES
H858 FGV -- Turbo auto
E981 KHM -- ES (509849)

Post Reply