battery light on at idle

[james butler]

ive got a funny fault developing on the rocko in the last two weeks. wen i start her ip from cold she idles about 750 rpm but the battery light is on, wen i give the throttle a blip above 1000 rpm the light goes out but the revs drop to 450 rpm so i give it more choke untill it warms up. ive tried tightenin the v belt up but hasnt had any effect. ive got a spare alternator and have tried swappin the brush pack and the black box thing i think is a suppresor? that also made no difference. any ideas?

[DannyH]

New fan belt?

[james butler]

yeah i put a new one on 3 months ago. old one fell apart.

[Ryan]

yeah i put a new one on 3 months ago. old one fell apart.

Try getting it tightened - It may have stretched a wee bit by now.

[Nate]

the alternator isn't spinning quick enuf to start charging. so long as the light does go out, it's not a problem. if it stays on, even very dimly, then you've got a problem with the alternator, or with its wiring

[james butler]

oh ok. to be fair it only does it when cold, just wernt sure if it was a sign of bigger probs to come or somthing.lol. thanks
james

[PeteGLi]

As said above - check the belt tightness.

Also check the blue wire from the alternator is connected properly.

[james butler]

have checked all the above but its still doing it. im just gonna take it as a quirk of the car. its not really that bigga deal and one day ile probably find out what it is, ile mek sure i let you all know.

[Nate]

my scala did this from when i owned to it when i moved up to a 2 litre. think it's often just an "old car" thing ;)

[hyperdrinky]

Check the brushes on your alternator. If they're worn they will not be contacting correctly and you will not get enough current through. Unscrew the two screws and pull them out of the back of the alternator. If there is only around 5mm of length then they're worn and you may need to replace them. Only about a tenner.

Hyperdrinky

[james butler]

i have replaced the belt and this seams to have cured the problem, the old one for some reason has gone realy shiny and no matter how tight it is all it wants to do is slip.at least this has fixed the problem.

[james butler]

ahh not again. the lights flickering again! im thinking that one of the diodes is goin in the diode pack. as it only flickers on under 2000rpm what do you guys think? ive changed brushes and the black supressor thing on the alternater to no avail.

[MrP]

I had the same problem and tried everything!! I;m currently doing an engine conversion and found out whilst stripping my original loom that the main wire from the alternator was absolutely shagged, it looked fine upon a normal inspection but when I removed the entire loom it practically disintegrated!

[james butler]

i took the alternator out and droped it down to the local car sparky, he tested it and turns out one of the diodes in the rectifier is fried. hes gonna try get some replacement parts tomorow and let me know of the damage.it got to the point on friday that with the engine idling if you turn the fan on the battery light came on and dropped the revs to 200rpm. when i put a multimeter on the battery i was getting 13volt at idle which dropped to 11.5 with any one load turned on.but hopefully will be sorted by 2moro afternoon.
cheers for all your input.
james

[james butler]

have now got a new alternator, and have just fitted it. the cars running a lot better and the battery light now goes out completely with the engine running. altho when i turn the fan on full or turn the foglights on it seems to sap a lot of the power making the revs drop. how much on average should the revs drop when you switch the fan on full or switch the foglights +headlights on? mine idles at 950rpm and drops to 650rpm is this normal.