battery not being charged?

[allyrs]

I'll start off by letting everyone know- i dont really understand electrics that well (not handy with a chim) but im learning fast!
since i have had the car i have fixed a nuber of problems to bring the car up to standard and the last on my list is to fix my battery going flat!
I dont believe there is a drain since i disconected the positive lead and ran a multi meter accross it. the battery when standing just now reads 12.3v and when the car is on it reads 12.7 so i guess its charging. but this doesnt seem very high? should it not be up high 13's when the engine is running?
the car has a brand new alternator leading me to believe the owner before thought this may be the problem. It looks earthed but all the cables come together and are hard to trace.
how is the battery actually charged?
any offers of help or teaching will be appreciated.
regards,
ally

[edtvr]

Have you had the battery checked out?
If the plates in the battery are distored the battery loses it's ability to hold a charge.
I would suggest you get it checked first before looking deeper.

Ed.

[GreenV8S]

If the alternator is charging correcting you should have around 13.8V across the back of the alternator (be VERY careful not to short the probes against anything when you measure this or you will get a very expensive bang). You should also see a similar voltage across the battery. If the alternator reads OK and the battery doesn't, I would suspect that the 100A fuse between the alternator and the battery has failed - they're a notorious weak point.

[allyrs]

the battery is brand new. i have to carry my other one in the boot and a booster pack just incase. ok so how do i measure accross the alternator? i dont like the sound of an expensive bang lol! where is the fuse would it be easier for me just to examine it? also what is the battery earthed to? many thanks

[tahiti450]

allyrs said:

ok so how do i measure accross the alternator? i dont like the sound of an expensive bang lol! where is the fuse would it be easier for me just to examine it? also what is the battery earthed to? many thanks

If you are unsure about acces ot the alternator output, probably easier to check the fuse, which is situated in a rectangular black box about 3 x 3/4 inch attached to the right side of the cylinder block lower skirt just above where the sump bolts on (just above the cross-bolts, if fitted)it'll have a thick cable entering and exiting one going to the alternator and the other to the battery. It has a cover which if removed reveals a thin metal strip fuse, this will probably be frazzled, or, as with mine, the whole holder will be fried. As a temporary fix the two cables can both be bolted to one of the posts on the holder (ensuring that the insulation is intact and that the whole thing is secure and can't short to earth). The purpose of the fuse seeems to be a matter of debate, as its an oddity, but my theory is that its there to reduce the risk of fire with the GRP body in the case of a major shunt causing earthing of the alternator to the chassis.

[allyrs]

cheers ill give that a shot when i get a min. but if it were blown i guess there would be no charge accross the battery- and mine has a very small increase in power?

[Cider Andy]

The fuse tends not to blow: it (and its holder) break down. So it's possible that it is not yet open cicruit, just showing high resistance which could explain why you have a slight rise in voltage at the battery terminals with the engine running.

One other thing to note about this fuse. It's not fitted in exactly the same spot on all cars. Mine's fixed to the chassis just in front of the starter motor. Quite a few owners have reported that their car doesn't have this fuse, so don't be surprised if you can't find it.