my car has developed a strange problem. I think its just a duff battery that's brought on by the cold. I have a group a coil/loom that takes power directly from the battery. it has ran flat twice now and I have since charged it and its ok for a day or two. today I started the car, struck up straight away, left idling for 5-10 mins then it just cut out. went to start and the battery is dead again. is it possible that the coil/blowers are taking more power from the battery than the alternator is able to charge at idle speed (950rpm ish). or is it just a duff battery.

 

Probably alternator output is low, start it up and let it idle. Voltage across battery should be around 14.5v. Turn some electrical items on like lights, heated rear screen and blowers etc then check the voltage at the battery again. It should stay above 13v, any lower than that and you have a dead alternator or bad wiring between alternator and battery.

 

Has the wiring always been like that?

Your warning light should illuminate if you have charging issues, it does not matter where it's wired from, the power still comes from the same source ultimately, but no that load won't cause an issue under normal circumstances.

Martin

 

As a rough rule of thumb good alternators can usually keep up with a duff battery when the car is running, duff batteries usually cause a problem running down on charge over night (wont crank over after being stood).


as your car starts fine from being stood then packs up shortly after I would guess the car is using everything the battery has to offer and the alternator aint putting it back in (not charging)


alternator warning lights don't always come on, if you don't have access to a battery drop tester then im sure your local garage would be happy to check your battery for free as they could potentially sell you a new one, just keep an eye on there results and ask that they show whats going on.

 

Also this may sound real obvious but its worth checking you've not spat the alternator belt???


(Advice - don't put your fingers in there when its running, this can result in a sharp stinging sensation followed by rapid loss of the red stuff)