Battery Light On, But Charging Fine...?

[Bovien 6]

My battery light just came on today after 10 min of idle. I drove through stop and go traffic without issues and it starts up fine.

Coming home, I measured 12.3v on the battery, 14.2-14.6 with engine running depending on revs and 12.8v just after shutdown winding down to 12.3 again. So all measures out fine as far as I can find. Why is the battery light in then?

 

If I take the spade plug off the generator and start it up, the light is off. Don't know if that tells you anything...

 

Any ideas?

[acox99 74 1 Cars]

Iv seen it on a ka where it was a broken wire in the harness to the alternator. May be worth stripping insulation back and looking if it feels a bit hard and cracked.

[PhilNW 44]

Could be the alternator diodes/rectifier gone

[Slo 283 1 Cars]

Start the car up, turn everything electrical on including the heater blower rear screen heater if you have one and all lights then pop a battery terminal off, if it keeps running its fine. Some people say this is a bad idea but ive done it for years and never had anything go wrong. Light coming on and still working ok is usually a sign that the brushes are almost worn out and it will need refurbishing.

[petert 588]

The light is there to excite the alternator, however the alternator will excite itself as the revs increase anyway. If you haven't got 13.8-14.4V at idle you have a problem.

[Bovien 6]

I'm not sure what you mean by 'excite'?

I do have 14.2 @ idle rising to 14.6 with higher revs. Battery is 12.3+ when the car is off. So all seems good and suggesting that it is charging just fine.

But why is the light on?

[petert 588]

Not sure, but read this:

 

http://en.wikipedia.org/wiki/Alternator_%28automotive%29

 

Field Regulation - 2nd paragraph

[sport1901966 8]

If you just connect the spade plug off the alternator to ground with the ignition on does the light come on or stay off. The dash light is connected in between 2 opposing 12v sources, if either one is off the then light will come on as there will be a potential difference across the bulb and current will flow.

 

Do the above test, if the light stays off then the 12v source the other side of the light is faulty (check the wiring diagrams for exactly where that source is).

 

The other check is to put one wire of a multimeter on the spade connection on the alternator and the other to ground while the engine is running - this should read 12v. If it doesn't that will be your problem, and considering the alternator is charging as it should, it suggests the take off from the field coil wires that feeds the spade connector is faulty within the alternator

[B1ack_Mi16 67]

My 405 diesel did something similar yesterday.

 

Battery light came on, it's not fully lit, but at idle it lights up pretty good. At 1500-2000rpm it's not so bright at all.

Above 2500rpm it goes away.

 

So just to change alternator then, faulty diodes or something?

[jackherer 543]

A dim battery light can be caused by a bad electrical connection somewhere between the alternator and the battery.

 

I once had a dim battery light for months then suddenly it came on brightly. The ring connector on the alternator had snapped off so I crimped a new one on, the bright battery light went out as expected but it wasn't even lit dimly any more, the connection must have been slowly failing for ages.

[DamirGTI 342]

I once had a dim battery light for months then suddenly it came on brightly.

 

Had just the same issue once , but in my case it was alternator going bad . More precisely voltage regulator part of the alternator (replaced the regulator and all was fine again and the battery light turned off ..)

 

D

[Slo 283 1 Cars]

The brushes wear down and also the slipring gets grooves worn into it too from the contact with the brushes this is why the light comes on, its on to say there isn't a full charge. Get your alternator replaced or refurbished before it lets you down completely on a freezing cold raining dark night in the middle of nowhere

[Bovien 6]

If you just connect the spade plug off the alternator to ground with the ignition on does the light come on or stay off. The dash light is connected in between 2 opposing 12v sources, if either one is off the then light will come on as there will be a potential difference across the bulb and current will flow.

 

Do the above test, if the light stays off then the 12v source the other side of the light is faulty (check the wiring diagrams for exactly where that source is).

 

The other check is to put one wire of a multimeter on the spade connection on the alternator and the other to ground while the engine is running - this should read 12v. If it doesn't that will be your problem, and considering the alternator is charging as it should, it suggests the take off from the field coil wires that feeds the spade connector is faulty within the alternator

 

Good info, I'll look into this

 

The brushes wear down and also the slipring gets grooves worn into it too from the contact with the brushes this is why the light comes on, its on to say there isn't a full charge. Get your alternator replaced or refurbished before it lets you down completely on a freezing cold raining dark night in the middle of nowhere

Can I use one from other period pug's? That would be a lot easier. How about 106's or?

[DamirGTI 342]

Mostly all XU alternator would fit so i'd go for the alternators from XU PSA engines rather than TU ones ..

 

I've replaced a few std. 205 alternators before with an 1.9 TD XU alternator from Citroen Xantia , and also from 2.0 T XU Peugeot 605 .. that was what i had spares but i'm sure virtually all the XU alternators will fit (some straight fit , some with minor mods mainly to the belt tensioner adjuster mechanism)

 

D

[Bovien 6]

If you just connect the spade plug off the alternator to ground with the ignition on does the light come on or stay off. The dash light is connected in between 2 opposing 12v sources, if either one is off the then light will come on as there will be a potential difference across the bulb and current will flow.

 

Do the above test, if the light stays off then the 12v source the other side of the light is faulty (check the wiring diagrams for exactly where that source is).

 

The other check is to put one wire of a multimeter on the spade connection on the alternator and the other to ground while the engine is running - this should read 12v. If it doesn't that will be your problem, and considering the alternator is charging as it should, it suggests the take off from the field coil wires that feeds the spade connector is faulty within the alternator

 

Ok, results are as this:

I took the spade plug off the alternator and directly attached it to a bolt, engine and others, and the light is still off. From what you say, that would put the error on the other 12V source to the dash light. However, I've looked at the wiring diagrams and can't find anything else connected to that light. The dash is no. 64 and the connection is "b" on the Haynes diagrams. On all the diagrams where 64b is connected, it is connected to the spade plug on the alternator. Am I getting something wrong here?

 

Other test I connected the multimeter to the spade connection and other to ground @ engine or bolt again. It tells me 1.5v when the ignition is on and 1.7v when the engine is running. Both sounds wrong and I'm guessing the difference is due to the alternator charging?

But if the alternator is bad, how come it seems to be charging the battery fine @ 14.2-14.6v?

 

Hope you can help here, but I'm guessing I need to find another alternator?

 

Thanks again

[jackherer 543]

If you're not seeing the battery light come on when you ground the wire you have a wiring fault, follow that wire back to see if you can find any damage.

[Bovien 6]

If you're not seeing the battery light come on when you ground the wire you have a wiring fault, follow that wire back to see if you can find any damage.

 

Thanks, but that can't be right in my mind, as the light is on, when the spade plug is connected to the alternator, but the light is off when it is not connected to anything or if I touch a grounding point. So something must be going through?

[jackherer 543]

Are you sure you had the ignition on when you grounded the wire?

[Bovien 6]

I did, as I saw the parking brake light being on (and I did turn past acc ). Tried several times with different grounding points within the few inches reach of the wire.

Edited November 30, 2013 by Bovien

[jackherer 543]

Try again, maybe with a bit of wire straight to the battery negative post. I'm not making it up The only way the battery light can come on is when that wire goes to ground.

[Bovien 6]

Will do. So, to check, would I also be able to connect the spade plug to postive on the battery and see the light turn off? Or would that screw something up?

[Slo 283 1 Cars]

Where did you get that idea from? The +D (spade) terminal will be live when there is a charging problem, usually it will be because the alternator isn't or cant rather create enough current as the brushes will start to short out creating surges then eventually contact will be lost and then the light will come on fully.

 

Connect your spade to a live and see if the light comes on, then just to satisfy your own curiosity connect a light bulb from earth to the +d terminal on your alternator.

[Bovien 6]

I understand that the spade on the alternator will be live 12v when the alternator is functioning and 0 or low voltage when it isnt. Hence the dash light comes on when the spade is off or grounded. As I can figure, the dash light shows a different in voltage between sources, so I though to check the wire, that if I connect it to 12v, the light would turn off?

Edited November 30, 2013 by Bovien

[jackherer 543]

This is a simplified circuit diagram of an alternator light, you can see how grounding the wire (at D+) will make the light come on if there are no faults.

 

[Bovien 6]

ignore this last post

Edited November 30, 2013 by Bovien