Engine idle ruff with lights on?

[Hyper]

Hi all,

My girlfriend recently purchased a 2002 nissan micra which has been running fine apart from one slight problem. When it first starts the idles fine with the lights on or off but once its been running for 10 to 20mins it idles ruff with the lights on, or the heaters or anything electrical. If the heaters are put on full the revs drop for a split second and the car almost cuts put. I suspected a failty alternater at first but apparantly revving the engine should make the lights flicker or get brighter but they dont change.

Could it be a faulty battery and is there any further tests i can do before replacing the battery?

Thanks, Sam

 

[rodenal]

Sounds like a dog

You want to check the voltage over the battery with the engine both off and then running. This should help check whether the alternator is sending a proper charge or not.

You can also piggy back off the alt connection to make sure its sending full charge (or not) from there. This will help determine whether there is an issue with the wiring or the alternator itself

I assume its an auto tensioner on the auxiliary belt on a micra so that shouldn't be an issue unless the belt is ancient and slipping

 

[Fuzz]

does it get progressively worse the more accessories you turn on? If so it is beginning to sound like a serious voltage drop happening. Whether that is due to a dodgy connection (earth strap) loose battery terminal, duff battery or a non charging alternator is up to you to find out.