Need new alternator?

Freddybob · 5 March 2018 at 1:49AM

Hi,

The red battery warning light came on on my dashboard when I turned my car (2006 Peugeot 107) on a couple of days ago. I managed to drive it back home ok, then left it for a couple of days before trying to fix it as I've been busy. As of yesterday the battery had gone flat and I couldn't start the car at all.

Last night I took the battery out completely, gave all the surfaces and electrodes a clean with sodium bicarbonate, and charged it with a battery charger. However this morning I still couldn't turn over the engine so I called the AA - the mechanic managed to turn the car back on and the battery light was no longer on.

However the mechanic said that since the battery light had come on, the car's alternator must need replacing. He tested it with a voltometer and it was above 14 the whole time which apparently meant it was working at the time, but he reckons it's definitely going to die on me again.

I've looked around and this looks like a relatively expensive repair, which obviously I'd rather not undertake if I don't have to (especially as a skint student)!

Essentially my question is whether a single instance of the battery light coming on means that the alternator definitely needs replacing?

Cheers

Sam_Fallow · 5 March 2018 at 2:48AM

If it is reading over 14 volts whle running then that points to a good alternator. If you charged your battery and it still wouldn't start but did when the recovery jumped it, then it sounds like a failing battery.

Any cold period of weather can see off a poor battery.

If money is tight then try a scrap yard for a cheap replacement.

parking_question_chap · 5 March 2018 at 8:20AM

How old is the battery?

arcon5 · 5 March 2018 at 9:27AM

Did he load test the battery?

AdrianC · 5 March 2018 at 9:32AM

The "battery light" doesn't tell you anything about the battery. It's a charge light, and it tells you that the charge voltage is not what it should be. The alternator generates charge, the battery stores it.

If you charged the battery last night, and the car won't start this morning, then the problem is the battery. ASSUMING the failure to start is due to a shortage of electrickery (dash lights on with key to normal run position, dim or off and whuuuurrr-whurr or simply click with key to starter position)

A dying alternator may well have taken the battery with it.

VERY basic diagnosis will tell you what's what. Plug one of these into the ciggy socket - https://www.ebay.co.uk/itm/391918395276
Anything lower than 14v when the engine's running? Alternator.
Charging OK, but anything lower than 12.5v with the engine off? Battery.

A decent-brand battery should be £50 or so for a 107 (size 002L), and an alternator is £75 plus an hour or so for fitting.
http://www.mister-auto.co.uk/en/alternator/valeo-436489_g4_a021436489.html

Freddybob · 5 March 2018 at 10:11AM

Thanks all for your replies.

The mechanic did do the test with the voltometer and it ran above 14V the entire time - does this reliably rule out problems with the alternator? I have a trip from Leeds to Southport planned this weekend and as you can understand I!!!8217;m now feeling a little nervous about that, but equally don;t wanna waste money to repair a perfectly good alternator!

Raxiel · 5 March 2018 at 11:52AM

Could the belt have been slipping?

arcon5 · 5 March 2018 at 11:57AM

Freddybob wrote: »

Thanks all for your replies.

The mechanic did do the test with the voltometer and it ran above 14V the entire time - does this reliably rule out problems with the alternator? I have a trip from Leeds to Southport planned this weekend and as you can understand I!!!8217;m now feeling a little nervous about that, but equally don;t wanna waste money to repair a perfectly good alternator!

Sort of. He could have also done a amperage check but personally I think your battery knackered.. If fully charged it could be the voltage is dropping too much on cranking. A battery load test can check this.

If it starts I'd take it to a garage and ask them to do a battery check. Even the nationals can't get this wrong. The testers are something any workshop will have

Freddybob · 5 March 2018 at 12:59PM

Raxiel - I hope not, the belt was only changed in December! Looks ok to me although I'm not a mechanic

Arcon - thanks for the tip, I've booked into Halfords for a free battery check tomorrow, will see what they have to say!

Raxiel · 5 March 2018 at 2:58PM

Freddybob wrote: »

Raxiel - I hope not, the belt was only changed in December! Looks ok to me although I'm not a mechanic

Arcon - thanks for the tip, I've booked into Halfords for a free battery check tomorrow, will see what they have to say!

I'd expect it to squeal if it was loose, but a new belt makes it more suspect to me. A brand new belt may need the tension re-adjusting after its been run for a while. If there were a lot of electrics on (particularly things like screen and seat heaters) the extra load on the alternator may have made it more inclined to slip.

It's possible there isn't one single fault, and a combination of things just happened to come together in the cold weather to create a more obvious issue.

Just a thought.

thescouselander · 5 March 2018 at 5:44PM

Could be the brushes on the alternator. If they're wearing out you might well get a good voltage reading under no load but it will drop under large loads such as when the rear demister is on.

Might be best to get an auto electrician to look at it. If it is the brushes these can usually be replaced at relatively low cost.

Need new alternator?

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