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[mark.adams]

When its cold and the car is just started and idling, with the fan on high, heated rear window on and lights on, the alternator light is just barely on, really dimly, if i turn stuff off, it goes out.
Is this a symptom of the car sucking more out of the battery than the alternator is putting back in?
Do i need a new battery or my alternator looking at???

[Andy B]

When its cold and the car is just started and idling, with the fan on high, heated rear window on and lights on, the alternator light is just barely on, really dimly, if i turn stuff off, it goes out.
Is this a symptom of the car sucking more out of the battery than the alternator is putting back in?
Do i need a new battery or my alternator looking at???

I'd suspect the alternator. You might be better taking it off yourself & taking it to a proper local autospark for him the check if you don't want to fix it yourself. Or A N Other from a breaker - unknown quantity though   

[Martian]

When its cold and the car is just started and idling, with the fan on high, heated rear window on and lights on, the alternator light is just barely on, really dimly, if i turn stuff off, it goes out.
Is this a symptom of the car sucking more out of the battery than the alternator is putting back in?
Do i need a new battery or my alternator looking at???

Neither, the alternator doesn't get properly going until the engine speed is above 1500rpm or so.

[Radar]

It will be sucking out more than is being put back in. It takes about 15 mins of running before charge gets put back in. If your idling can you not turn the lights off to save battery? You could always get a free battery check from halfords to see if the battery is charging ok (if they still do it).
Do you give your car enough driving to charge it up because if you don't and your journeys are short then the battery will drain.

[Andy B]

.....
Neither, the alternator doesn't get going until the engine is at an absolute minimum of 1500rpm

maybe true when the world was black & white and cars used dynamos and regulator boxes, but modern alternators will be charging from virtually tick over. 

[Andy B]

.... You could always get a free battery check from halfords to see if the battery is charging ok (if they still do it).
......

Would you really trust a spotty yoof from Halfords?  You need to take your cars to a proper autospark for battery & alternator testing. 

[Lazydocker]

First thing I'd check is that the battery crimps are secure... Classic symptoms of bad crimps IMHO

Not just secure on the post either, I'd bet £1 that the wiring into the crimps is in bad condition Check whether the wires/terminal crimps are getting hot (be careful, they can get very hot!!!)

[Andy B]

First thing I'd check is that the battery crimps are secure... Classic symptoms of bad crimps IMHO

Not just secure on the post either, I'd bet £1 that the wiring into the crimps is in bad condition Check whether the wires/terminal crimps are getting hot (be careful, they can get very hot!!!)

It made a difference with my car. I borrowed a LARGE set of crimp pliers from work to re-work the crimp on mine 

[Abiton]

http://www.omegaowners.com/forum/index.php?topic=90619.0

 

[freecall666]

mine on tick over reads 14v+, when driving read 13.85v with no lights on etc

[Martian]

.....
Neither, the alternator doesn't get going until the engine is at an absolute minimum of 1500rpm

maybe true when the world was black & white and cars used dynamos and regulator boxes, but modern alternators will be charging from virtually tick over. 

My money says it is the case in this example Andy.

Off the top of my head I'd say that the headlamps, fan, and heated rear window combined have got to be pulling a good 20 amps or more, and the alternator simply won't be able to produce that current when the car is idling.
An alternator is considered good if it can make 13.8 - 14.4V with the lights on and the engine at 2000rpm.

Add in the fact that a fair chunk has just been sucked from the battery because the car has just been started (it takes a good 15 mins of driving to put back in what it took to start the car), and it's no wonder the alternator can't keep up with having to charge the battery as well as deal with such a demanding load at idle.

[mark.adams]

Nice one.
Thank you everyone, i have a few things to look at there, i do turn the lights off when idling, i just noticed when pulling away the other morning, it was raining so windscreen wipers were on, blower on screen as misting up, heated rear window on same reason and i could see a dim glow on the alternator light, i switched off the heated rear window and turned the blower motor down and it cleared okay.
Never have trouble starting the car by the way...

[Kevin Wood]

I would say that an alternator light starting to glow with increased load is indicative of either a poor electrical connection or possibly a failing rectifier pack on the alternator.

First check, as said, is the battery positive terminal, as the crimp often gets loose here. Run  it with plenty of load on and the battery terminal will get hot.

Also check the negative terminal and all connections between the negative terminal, chassis and engine block, including the various straps between block and chassis.

Check the positive connection to the alternator (again, it will get hot if the connection is bad, but may be masked if the engine is also hot).  Sometimes, the alternator mountings can corrode, and since these form the negative connection to the alternator, this can cause poor charging. If nothing else helps, take the alternator off and clean up the mounting faces on alternator and bracket with a bit of wet and dry.

It is often worthwhile connecting a voltmeter between alternator positive terminal and battery positive terminal, and then alternator casing and battery negative terminal. Any voltage drop here will indicate a poor connection. I'd expect only a few tenths of a volt with some decent loads drawing current.

Also run through the starting and charging guide and see how well it's charging.

[Guinney1971]

I've had the alternator light dimly glowing on my car, just as the OP described too.

I sometimes only do a short run each day of less then 2 miles, depending where my daily chores send me, and last Sunday the car wouldnt start, but after a good run (to Donington), the car was fine, and even started ok when we left, despite the boot light being on for over an hour cos we were sitting in the load area.

I'll dig the test meter out and see what the voltage levels are, then worry about it from there - will also check the battery crimps as has been suggested, I'm lucky to live not far from the excellent Vehicle Wiring Products who are in Ilkeston, Derbyshire, so if I need owt I'll get it from there.