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flat battery


toyroom

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OK, so it's not flat, it's sqare...Has anyone heard of a battery going completely flat and then failing to hold charge therafter ? I have heard of this and a local expert has also. Basically, I have not seen the charge light on the dash for a while (Which can mean the bulb has gone and therefore so has the switch-on for the alternator. The car has had more problems than you can shake a stick at in the last twelve months and has therefore been on the battery conditioner a lot. This has created the illusion of a working charge circuit with the car running on battery alone. This week it went back to work for the first time without conditioning and sure enough, after standing with the alarm on for a whole day...no power at all in the battrery...not even enough to light the alarm LED. Once the car was jump started, it stopped about 20 seconds after disconnecting the jump leads. Hence: dead battery and dead charge circuit. I charged the battery overnight and then left the car locked and alarmed with the conditioner connected. 1 hour later, alarm goes off and the alarm was then switched off and the car left open with the battery connected but everything off. 8 hours later, got home to find battery totally flat agin and conditioner failing to "top up" when turned on. Conclusion: charge bulb probably gone and hence charge function not working; alternator maybe OK, don't know, battery, well, what does anyone reckon ?

I was going to get a new battery and try and change the bulb in the warning light...how the heck do you get the binnacle off ?

Any comments on the whole story would be welcome.

The car drove home 7 miles absolutely fine with a spare battery connected by jump leads.

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It may be worth checking electrolyte levels in the battery, as that would stop it holding charge.

If the bulb isn't coming on when you turn the ignition to on, then you are a naughty person who should have dealt with it sooner. tsk tsk.

You'll need to remove the trim in that side of the binnacle, then there are two screws that hold the row of lights in place. It's a relatively easy, quick job. Re the charging circuit, I'd suggest getting a volt metre across it, you should be getting IRO 14 v when charging, if you get nothing it could be as simple as a connection off.

Andy

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I've been fortunate to not have any charging issues on mine in the few short months of ownership, however from previous vehicles I've had I can only share my own personal experiences. You should have a charge indicator light when the key is just turned on with the engine off. If this light isn't working I'd first suggest replacing the bulb. I have seen where a failed bulb can actually cause the alternator to stop charging since in some wiring systems the bulb is actually a vital part of the charging circuit. The other option I can offer is to locate a known good battery, start the car and verify that you have somewhere in the range of 14V at the battery posts with the engine running. I would also suggest checking all the fuses to ensure that none are blown, and it might not hurt to remove each one (one at a time) and reseat them in case something isn't making a proper connection.

Looking at my schematic, it looks that you should have a battery connection to the heavier gauge wire going to the back of the alternator. If you have a continuity gauge, check that you are getting near 0 ohms on this to the positive terminal on the battery. This is the high tension lead to charge the battery. You should also be receiving the same 0 ohm reading between the body of the alternator and the negative terminal of the battery. You should also find a 2nd wire which is the field wire that tells the alternator to begin charging. It looks to me like this is initiated by the ECM at pin 58 connecting at the dash to what seems like a connection on the tachometer (?) through the ignition warning lamp (charging indicator) and finally to the field terminal on the alternator. If you need a scan of the image, let me know and I can scan and send what I have.

Blake

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Has anyone heard of a battery going completely flat and then failing to hold charge therafter ?

That's generally the way that modern batteries fail. One minute they are fine, then you come to the car and it's flat. Charge it up, flat again in a very short space of time. I've had that at least twice that I can think of.

The battery light on the dash should come on when you turn the ignition on and then go off again. If it comes on whilst driving it means the alternator is not charging the battery. So, of your battery has had it the battery light wont indicate that - it will only indicate there is a problem with the charging circuit.

Conclusion : Your battery is f*cked.

Right then, said Fred.

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A battery can completly die, your local motorfactor can test it for you. if it's dead you need a new one, the plates buckle and then won't charge correctly. perhaps the car was draing more current then the conditioner could supply? i.e even though you had it connected the battery was still dischargeing.

Aklso be aware that a completly flat battery can switch polarity! I have had this, never realised that it can happen until it did, (the main fuse went bang when I connected it!) then I read up on it on google.

Amateurs built the Ark

Professionals built the Titanic

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  • 1 month later...

:) The answer !! When we got the alternator off, it was compleetely shorted both ways. I deduce from this that the diodes in the rectifier were not working as diodes anymore. The bulb in the dash was gone. Replaced both, and the battery and car now performing like a rocket sled. Admittedly it was wet, but wheelspin at 75mph with a limited slip diff installed is pretty impressive. All the electrical stuff is working better (brighter lights etc.). Looks like this is what happened (is this possible?):

Alternator partially fails with intermittent DC charging; alternator shorts the charge light on the dash which then stays on all night and overheats the bulb causing it to fail; alternator now stops being excited into working but battery conditioner keeps battery full enough to get me to work and back for a couple of weeks.

Eventually, the battery is not charged enough to be still alive at the end of a long day and the whole thing is dead.

I jump start the car off the wife's car (Esprit unpopularity hits all time low in the freezing December dark night) and foolishly take the jump leads off with the engine running, probably rogering what was left of the alternator.

Then I found out that the bulbs are no longer available (2W caseless) but that 3W will do. Jon came to the rescue with a '97 instrument binnacle complete with bulbs. (and a spare battery--one of the benefits of an Esprit enthusiast just up the road from the office!)

So, in case this helps in the future:

1. The charging circuit only works when the bulb does.

2. You can use 3W bulbs.

3. Battery conditioners are great for holidays but probably best left off for the rest of the year.

4. Always carry jump leads.

5. Don't take the jump leads off a flat battery with the engine running.

6. The best way to get home with a flat battery (and no alternator) is probably with jump leads and a spare fully charged battery.

7. The secondary injectors have TWO O rings on them...See the O ring post !!

Edited by toyroom
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