Voltage Low & Battery Flat - But Alternator And Battery Good?

[boostdef]

Hi All,

I know immediately you think this is either alternator or battery, but it is not as I have replaced both!!!

Ok, start the car and the volt gauge sits just below 12, and the multimeter across the terminals shows about 12.5. Once something like headlights, thermo fan or similar goes on, this drops to about 11, and keeps dropping until the battery is flat.

The funny thing is, if I disconnect the battery, the reading across the terminals goes up to 13.7 (normal). And I can turn on headlights and so on, and the alternator takes this charge.

I have checked all fuses and wires, and I am STUMPED! Earths seem good ??

Car is a 1991 Ford Capri COnvertable.

Any suggestions?

[blind_elk]

First silly Q - if you have disconnected the battery, then which terminals are you measuring voltage across?

What do you mean by "alternator takes this charge"? The alternator "makes" charge.

[boostdef]

First silly Q - if you have disconnected the battery, then which terminals are you measuring voltage across?

What do you mean by "alternator takes this charge"? The alternator "makes" charge.

With battery plugged in and say I turn the lights on, the Volts drop to about 10 across the terminals and on the volts gauge.

If I do this with no battery connected whilst the car is running, and I turn the lights on, the Volts remain at around 13.4 no matter how many accessories I turn on.

With the battery connected(tried 2 batteries, 1 is brand new), if I turn on all accessories the battery is drained pretty fiercly. With the multimeter connected you can see it going down in Volts at a rate of knots.

[jnr_chin]

With battery plugged in and say I turn the lights on, the Volts drop to about 10 across the terminals and on the volts gauge.

If I do this with no battery connected whilst the car is running, and I turn the lights on, the Volts remain at around 13.4 no matter how many accessories I turn on.

With the battery connected(tried 2 batteries, 1 is brand new), if I turn on all accessories the battery is drained pretty fiercly. With the multimeter connected you can see it going down in Volts at a rate of knots.

so u have eliminated the alternator belt as well? the battery in this case is considered a load so it is normal for it to throttle down the engine but whats the reading after awhile when connected properly. the battery supposed to go back up to 13. .....the light and stuff are more loads so that is normal but the battery not taking the charge and is considered new. that is strange

[SXC-R34]

THAT IS WIERD. Solution: SELL THE CAR LOL N buy a skyline LOL

[cosmic starz]

so u have eliminated the alternator belt as well? the battery in this case is considered a load so it is normal for it to throttle down the engine but whats the reading after awhile when connected properly. the battery supposed to go back up to 13. .....the light and stuff are more loads so that is normal but the battery not taking the charge and is considered new. that is strange

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WELL THE EASY ANSWER IS TAKE THE CAR TO A AUTO ELECTRICIAN

BUT IF YOU DON'T WANT TO DO THAT JUST YET YOU NEED TO MAKE SURE BOTH BATTERIES ARE GOOD - OLDER ONE MAY HAVE CELLS BREAKING DOWN AND ITS NOT IMPOSSIBLE FOR A NEW ONE TO BE A DUD OCCASIONALLY - YOU CAN CHECK ALL CELLS EASILY - GOOGLE HOW TO DO IT - AND DO IT WITH THE NEW ONE TOO

ALTERNATELY YOU CAN ELIMINATE THE BATTERIES AS THE FAULT BY PUTTING THEM IN ANOTHER CAR - IF IT DOES NOT GET SAME PROBLEM BATTERIES ARE GOOD

ALSO CHECK YOUR EARTHING - ADD SOME EXTRA IF NEEDED

AFTER THAT IF NO GOOD SEE AUTO ELECTRICIAN UNLESS SOMEONE ON SAU HAS ANOTHER SOLUTION TO OFFER

[JMW]

Sounds like a dead cell in the battery or voltage regulator on the alternator. Voltage when car is running and accessories on should be around 12-13 volts to compensate for usage and charging of the battery. Hook your multi meter up to the battery, start the car and give it a rev, if charge does not rise i'd be looking at thr regulator