What's likely to be wrong with this car?

[NY]

"D.M. Procida" wrote in message news:1n2m8yi.x5uyosljjd50N% [e-mail]...

Yes, it sounds as if the battery is holding its charge.

Take the fully charged battery and connect it into the car overnight, with everything switched off. After dark, go round and check for any lights (eg interior, boot) remaining on when the car doors are closed.

If the battery won't start the car the following morning, it's stray current drain - something somewhere is drawing current when it shouldn't.

This is independent of whether or not the alternator is working properly to charge the battery in situ, so as to replace the charge used to start the engine, and to supply the car's needs while running.

Once you've eliminated stray current drain, then you can move onto the second stage of whether or not the alternator is charging. The fact that you are getting 14V at idle tends to suggest that the charging circuit is working.

[dennis]

A dc clamp meter is useful at this point. About £30 from cpc.

[damduck-egg]

I haven't seen you mention a make/model/year of but it might be worth perusing the WWW for any owners forums for your car and see if any others have a battery drain problem or parasitic draw as some call it. I gave an Astra to my parents which had been my company car,unlike me they only drove it once a week and the battery was drained by some draw in the alarm/ immobiliser that was greater than normal. The local village garage did not have the knowledge/resources to get to the bottom of it. Dad just lived with it and left the car unlocked as it was kept in a shed on a farm miles from anywhere.

G.Harman

[Chris B]

And don't forget that sneaky glove box light (if you have one). It can be difficult to tell if the glove box light goes out when you shut the door.

[Harry Bloomfield]

That will not work on any modern petrol or diesel - the ECU will do its very best to maintain its programmed tick-over speed. What might be noticeable is a change in the tick-over engine note, as it comes under more load.

All of my lighting is fed via a constant voltage supply, so reving the engine up, makes no difference to their brightness.

[Dave Plowman (News)]

I've not found them very accurate for low loads. But haven't tried the very latest ones.

What I do with a DVM is to connect it in current mode between battery and terminal before disconnecting that terminal. So any switch on surge doesn't go through the meter. And obviously use the 10 amp range on the DVM initially. If that shows a nice low value you can then get the exact reading using a lower current range.

[Dave Plowman (News)]

If that shows nothing on but the battery discharges, charge the battery again and repeat with the alternator disconnected. Note the thick wire(s) are live at all times so make sure they don't short to any metalwork.

If a diode in the alternator rectifier fails, the alternator may still 'work' but draw current from the battery when the engine is turned off.

[Thomas Prufer]

Measure the current draw of the car when off: disconnect one pole of the battery, set multimeter to 10A, plug leads accordingly and connect multimeter in series.

Do NOT start the car (turn on the headlights, the window heater, radio, etc.), as this will draw far more that 10 amps and the leads will go up in smoke and fire. (Cheap multimeters will not have fuse protection in the 10 amp range. Please put the leads where them melting etc. will cause as little damage as possible.)

Check the reading, and reduce the range if appropriate, which may entail replugging the leads. The car should not be drawing more that say 100 milliamps. It probably will be drawing more, because I'm assuming something is draining the battery fairly heftily.

Start pulling fuses, one by one, replacing them for simplicity. Removing the fuse protecting the circuit that is causing the drain (and likely faulty) will cause the current drain to drop.

Then it is a question of finding what's wrong with the circuit. This can be trivial, or not...

Thomas Prufer

[Bob Minchin]

I've also had a leakage problem when water had got into the fusebox of my sons mk11 focus. Even though it had all dried out there was corrosion and growth between the metal busbars under the fuses. enough to give a

30mA continuous leak in addition to alarms, radio back up etc etc as found in a modern car.

[Dave Plowman (News)]

Think some of the earlier Escorts also had a fusebox in a silly position. Or just made so that is was prone to faults through damp.

[Dave Plowman (News)]

Some cars can take more than 10 amps when the battery is connected initially. And blow the DVM fuse - or worse.

Mine does. The central locking will trigger when the battery is first connected.

[The Natural Philosopher]

Well you have remade the connections.

It should be fine now as the lost likely explanation was a bad connection.

[harry]

You don't need any high tech crap. With the battery charged, disconnect it and then stroke the connector on the battery terminal. Do it in dim light. If current is flowing anywhere you'll see sparks. Even for a tiny current

If you don't this indicates the battery is not discharging into some component on the car there is some fault in the charging system.

Check for loose connections/broken wires appertaining to the alternator. The tin wire goes to the ignition switch. The thick wire goes to the battery. There may be an external rectifier or it may be inside the alternator (More common these days.

If the alternator is working, you should see the highlights brighten when you rev the engine in the dark.

The alternator can be checked out on the bench but you need instruments. The commonest fault is brushes worn/stuck.

[Dave Liquorice]

without

Yep, leave it and use as normal for a week or so and see if the problem returns.

[NY]

Surely the OP has remade the connections many times - every time the battery has been removed to recharge it and replaced to start the car. Of all the suggestions that people have made over the week that this thread has been running, that's one thing that you can discount: bad connections to battery. Bad connections to alternator and to ground are a different matter.

[Dave Liquorice]

I don't remember that being said. Charged yes but not removed other than when being replace by a new one months to a year ago.

[D.M. Procida]

I don't remove it to charge it (or even disconnect it)! Should I?

Daniele

[Dave Liquorice]

In theory yes, but who does?

Modern cars don't like having the battery removed, they forget to much.

[NY]

You charged the battery while it was still connected to the car? I thought that was usually likely to damage the electrics of most cars. It also means that you have to get a mains supply to the car and leave it and the charger unattended overnight, risky for theft if the car is kept on the drive.

The only time I've ever charged a battery, I've removed it, and taken it into the garage to the charger and its mains plug. I thought that was the only correct way to do it. Maybe I'm about to learn something :-)

[NY]

If the battery has gone flat, especially if the starter motor has been operated, the radio, clock etc will already have forgotten who they were, what time it is etc.