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Battery Goes Flat, Volts Low but Alternator and battery fine 

 

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 Post subject: Battery Goes Flat, Volts Low but Alternator and battery fine
Posted: Wed Mar 04, 2009 9:26 am 
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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?
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 Post subject: Re: Battery Goes Flat, Volts Low but Alternator and battery fine
Posted: Wed Mar 04, 2009 9:32 am 
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Something must be draining when it shouldn't be!

What auxiliaries have you got?

My old alarm was draining 3ah on arm, which made my battery go low in the morning.
Check amps, alarm, boot light, anything!

 

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 Post subject: Re: Battery Goes Flat, Volts Low but Alternator and battery fine
Posted: Wed Mar 04, 2009 9:35 am 
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I have gradually taken out all auxilary fuses and nothing seems to be it. It doesnt have any amps or anything as its my mothers car.

I just dont understand how it sits at 13.7V and can run all accessories without the battery plugged in, but when its plugged in it dies ??
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 Post subject: Re: Battery Goes Flat, Volts Low but Alternator and battery fine
Posted: Wed Mar 04, 2009 9:42 am 
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Are you sure the battery isnt just stuffed????
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 Post subject: Re: Battery Goes Flat, Volts Low but Alternator and battery fine
Posted: Wed Mar 04, 2009 9:43 am 
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Replaced it with one out of another car, and THEN purchased a brand new battery.

Also replaced the alternator and same symptoms.
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 Post subject: Re: Battery Goes Flat, Volts Low but Alternator and battery fine
Posted: Wed Mar 04, 2009 10:24 am 
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Hey I had a similar problem, the plug that went on to the top of my alternator was full of crap, gave it a good clean with crc and a wire brush and has been good as since. Had water dripping on it from a leaking expansion tank :roll:

 

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 Post subject: Re: Battery Goes Flat, Volts Low but Alternator and battery fine
Posted: Wed Mar 04, 2009 10:38 am 
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was the alternator a new one or a secondhand one??

if its secondhand it might be stuffed aswell..
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 Post subject: Re: Battery Goes Flat, Volts Low but Alternator and battery fine
Posted: Wed Mar 04, 2009 10:52 am 
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It has gone through 3 alternators in 2 months, so there is definately something wrong.

The alternator that was in there was brand new, but I replaced this alternator with one that was Known working 2nd hand.
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 Post subject: Re: Battery Goes Flat, Volts Low but Alternator and battery fine
Posted: Wed Mar 04, 2009 10:56 am 
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Forgot to add, The battery Light is NOT on??
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 Post subject: Re: Battery Goes Flat, Volts Low but Alternator and battery fine
Posted: Wed Mar 04, 2009 1:45 pm 
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EF_STOCKO wrote:
I have gradually taken out all auxilary fuses and nothing seems to be it. It doesnt have any amps or anything as its my mothers car.

I just dont understand how it sits at 13.7V and can run all accessories without the battery plugged in, but when its plugged in it dies ??

There's your answer right there.

 

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 Post subject: Re: Battery Goes Flat, Volts Low but Alternator and battery fine
Posted: Wed Mar 04, 2009 1:47 pm 
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Ive tried multiple batteries?
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 Post subject: Re: Battery Goes Flat, Volts Low but Alternator and battery fine
Posted: Wed Mar 04, 2009 9:09 pm 
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did you put an EL alt in to an ef? i think they have different amperage outputs or something

 

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 Post subject: Re: Battery Goes Flat, Volts Low but Alternator and battery fine
Posted: Wed Mar 04, 2009 9:17 pm 
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This is a 91 Ford Capri.

Alternator before this one was a genuine one from Ford, installed by ford ($380 later).

The one in now is from a wreck which was known working.

Cheers
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 Post subject: Re: Battery Goes Flat, Volts Low but Alternator and battery fine
Posted: Wed Mar 04, 2009 9:42 pm 
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ah soz.

have a quick look over the connections. SUPER RIDICULOUS bad earthing, regulator f**k itself major too

 

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 Post subject: Re: Battery Goes Flat, Volts Low but Alternator and battery fine
Posted: Thu Mar 05, 2009 11:00 pm 
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DO NOT RUN THE CAR WITH THE BATTERY DISCONNECTED.If you do this you will either [a] blow up alternator by destroying the rectifier and /or [b] blow the fusible link which supplies power to the alternator.So how many alternators have you f$^&*?The days of disconnecting the battery to test the generator went out when the alternator was introduced.So stop doing it,ok?Do not disconnect the twin plug which goes to the alt. while vehicle is running.To test your charge rate 1st.Buy a multimeter and learn how to use it2nd.Buy a testlight and learn how to use it.Now turn on ignition and make sure you have a warning light which looks like a battery.If you don't disconnect the twin plug and use your testlight to make sure you have 1[12 volts dc and the other if you use the testlight to earth it out should make the warning light turn on.If you do have a w/light then start the car.Use the multimeter to see what volts you have at the battery and at the B+ on your alt.13.6 to 14.4 volts is ok Rev the engine and recheck volts .Turn on a/c and headlights and check volts ,rev and check.if there is more than .3 v difference then either your battery needs charging or you need to fit another wire 6mm between alt and battery .ANY Q's ?
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