Electrical problem x type 2.5 auto

[Matt Ff]

When I say problem I mean I can force the battery warning light on. If I switch on front and rear heater with demisting the light pops up. Rev just above idle and it goes out. Occasionally it stays on until I switch of an on again. 

All other times the car is fine, charges battery and it holds well enough. Local garage is going to fit a new alternator for £400. The car has been doing this since Oct and hasn't got any worse.

Am I wasting my money? Is the ECU simply doing its job? Anyone else has this on their  x type?

Thanks muchly

Matt H

[Leo]

I certainly wouldn’t be spending that kind of money, or indeed anything at all: I would happily accept that if I am putting a very heavy drain on the battery I should increase the revs above tickover.

[JOE-DOT-COM]

Hi

Only way to tell is with a multimeter, start the car and the battery voltage should be above 14 Volts

get the light to come on and check again, if it drops below 12.5 volts, then its not charging enough

also check the belt, a slipping belt could also cause the same symptoms

cheers

Joe

[richdraper]

Sounds like your alternator is possibly on its way out or more specifically... the pulley... I'm led to believe they are overrunning pulleys, of some description (theres 3 different types use in the industry, I don't know which the 2.5 V6 is). £400 is really steep for an alternator replacement imo. You can pick remanufactured units up for under £150. The pulleys don't appear to be available separately although i haven't spent a lot of time looking.

I've had this on one occasion with mine seems to have been a bit of a glitch. The alternator is 120amp so should be able to keep up with any loads you put on at idle. 

As Joe said check battery voltage a) when off, b) when running, and c) with loads, when running.

I've found mine settles at about 12.4/12.6v if left overnight, running it fluctuates anywhere between 13.5v and 15v bear in mind a top end is generally considered to be around 14.2v-14.7v. Running with loads the alternator should still be able to charge the battery at at the very least 13.2v.  i dont believe its uncommon to see 15v when the alternator is cold... Alternators have a sweet spot for efficiency, if you drop out of that window weird readings can be encountered but I'd be worried if it's throwing a battery light even once.

If you want more accurate readings I can get them for you tomorrow

extra reading:-
http://www.daycoproducts.com/what-are-oaps-and-oads-and-how-do-they-fail