chung

Hi all ive got a bit stuck now. My pervious battery was boiling its fuild and the guy at the local parts store said that it was the alternator that was overcharging the battery. When he stuck a multimeter on it, it read 14.47 and said it was too high.

Ive spoken to a place about getting the alternator repaired and they said that this reading was normal and was probably a dodgy battery.

Im now a bit confused about what to do if anyone can help that would be fantastic.

Nick Graves

Alternator output varies according to load, but that's about right.

Is your new battery OK, or what?

Floppy

Forget about voltage to an extent. With the engine running the car should be reading about 30amps on the positive connection if the battery and alternator is good IIRC. If its lower than that, say 10-15amps it means the alternator is likely to be dying or dead and if its a lot higher say 80amps, it'll be the alternator over compensating to try and give charge to a dead battery.

HTH

unclefester

If the ELD ( engine load distribution) fuse has blown then it will be running in high charge all the time instead of varying it - however IIRC the ELD fuse blowing will throw a CEL.

Daytona-Dave

sounds about right, certainly not high,

aston19uk

stick a multimeter on the battery when the engine is off. Should read 11.4 volts or near to if I remember correctly to jump start the car. any lower that there be problems with battery or charging.
The alternator needs to charge at around 14.4 so that's correct.
probably a bad battery

Daytona-Dave

A fully charged battery is 13.2 volts most battery's settle overnight dependant on temp to about 12.5 to 12.8,

CHIPPO

14.4 volts is required to charge a 12v lead acid battery to over come the internal resistance of the battery and charge. Under 14.4 and it will not charge, over 14.4 and it will over heat and cause all sorts of problems. Now as i recall most 12 V batteries have 8 cells each rated at 1.5 v =12v connected in series. Hence a nominal output of 12V. Hence the requirement for a voltage regulator in the charge circuit to prevent too high a charge voltage. Have wound up the charge volts on small lead acid systems in the past they soon get very hot and smoke ! not very good !
So 14.47 is a tad high , but that could the multi meter misreading, is it calibrated , even so could still be that far out. I have a Fluke at the moment and it is usually fairly accurate. But its out of calibration and not to be trusted, especially at 2 decimal places.

Daytona-Dave

The car battery has 6 cells and when freshly charged either by a charger or alternator will have a surface charge of 2.2volts per cell, total 13.2 this will settle to about 12.6 fully charged , plus you need to check the amps you can't check a charging system correctly with just a voltage check, and it needs to be checked under load as well as idle,

CHIPPO

Ray , I am a numpty have severe brain fade this evening , I will now shut up. I must be on another planet and my flux capacitor has discharged