Revs drop under elec load

[seanr68]

Got an annoying prob with my Scala. The revs drop from around 950rpm to anywhere between that and 400rpm when I turn on anything electrical.
At first I thought it could be the weedy 55amp alternator, so I got a good working 90amp one to try cure it....didn't work though.
The problem isn't too bad in daytime, but obviously at night, its nigh on dangerous nearly stalling at every junction. The bigger the load, the more drop I see in the revs. The battery is a good quality one, and was new last winter.
Any ideas greatly appreciated.

[DannyH]

You could check the carbon brushes on the voltage regulator?

[wasted]

Isn't the voltage regulator built into the alternator? In which case, I'd have thought swapping to a different alternator with no change in symptoms rules that out.

I reckon it may be one of your earth straps - have a check to make sure they're connected ok. Other than that, it may be a short to earth somewhere in the car.

[seanr68]

Isn't the voltage regulator built into the alternator? In which case, I'd have thought swapping to a different alternator with no change in symptoms rules that out.

I reckon it may be one of your earth straps - have a check to make sure they're connected ok. Other than that, it may be a short to earth somewhere in the car.

Yeah you're right about the VR.
I've put a new earth strap on recently, i'll double check it though.
I'll just clean all the earthing point and see what that does. I suppose battery could be part of prob??

[wasted]

It's possible, but the amount of drain you'd need to affect the engine revs would be extreme. It seems to indicate that the alternator's having to work overtime to power everything. I'd personally recommend going over everything with a multimeter, including the alt and battery.

[Nate]

make sure that both ends of the main earth are clean and secure. check for a voltage drop between battery -ve and the engine, and battery -ve and the body.

although you say your battery is a decent quality one, is it the correct one for the car?

[seanr68]

Sorted the prob now....i copper slipped the earth straps and every other earth i could find. Job done.

cheers for feedback all.