battery voltage loss

Hi all,

Apologoies in advance for the usual lack of clarity. Just put a new battery in a few hours ago when the last one dropped to 3.3v overnight (even the clock stopped). Measured the voltage from the new one before it was installed and got 12.36 volts. Last two measurments were 12.10 volts then 11.96 volts an hour later (no usage of the car in between except the interior light for a few seconds to pop the bonnet). By my calculations that would give me 0 volts in about three and a half days. Something dodgy going on here? The car has sat for three weeks before now and started straight away afterwards. Have pulled the rear window heater fuse as it appears not to be working and thought it might somehow be broken in a way that is sucking the life from the battery even when everything's off but still getting this voltage drop. Ammeter got fried trying to test the new battery!

Anyone got any ideas as to what could cause such a drain on the battery? (no lights left on or anything obvious like that). Vehicle is a 96 escort 1.3.

Advice appreciated. Flames tolerated due to admitted ignorance.

Chandy

Reply to
chandy
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Assuming there's no hidden boot light or similar left on somewhere (which as you say, you've checked anyway) then the usual suspect is the alternator - one or more of the diodes can go short circuit allowing the battery to discharge through the stator windings. Although if you've got central locking, that can play up as well.

In your position without a working meter, I'd be inclined to disconnect the alternator and see what happens. Remember though, that the thickest wire is connected directly to the battery so you must make sure this doesn't short to earth.

If that doesn't stop the battery discharging then you need to get a replacement meter and check the current drain from the battery. Put the meter onto its highest ampere range, disconnect one terminal of the battery and put one meter probe on the battery post and the other on the connection you've just removed. A few tens of milliamps is normal, anything over that isn't. At the rate your battery is going flat though, there's a draw of several amps somewhere. Start removing fuses to isolate circuits and discover where.

HTH

Reply to
Ian Edwards

Vehicle

Would this not necessarily prevent the alternator from being able to charge the battery as it appears to be doing so. No central locking and there were no indications of a problem before all this other than the rear window heater seemed to stop working again, but as I said I already pulled that fuse.

disconnect

thickest

Sorry, not sure what you mean by that. Thought the -ve terminal was already connected to the body anyway? How would I disconnect the alternator?

Ahh, so you don't just connect in parallel over the terminals then? That might explain the now probably broken ammeter? (accompanied by almost melting wires on the meter and a puff of smoke) Glad the voltmeter part still appears to work. Would 10A be enough of a range?

About an hour later, down to 11.86. Better go disconnect it completely I think then play with the fuses tomorrow when there's some daylight and my better half might be more inclined to help.

Thanks!

Chandy

Reply to
chandy

Ok, with that little reminder to me of higher physics, looks like the ammeter survived afterall and there's a draw of 2.4 amps when it's sitting doing nothing. Have now disconnected the -ve for the night.

I take it if I go through all the fuses tomorrow and nothing helps then it's going to be the diode(s)? Easy/hard to replace? Think I read somewhere that they're not expensive?

I realise this is all a bit backwards from what you advised but best I can do right now.

Thanks again,

Chandy

Reply to
chandy

Do you have any additional audio equiment such as an amplifier which is permenantly fed power? The alternator is the most likely cause though. Try disconnecting the wires from it as a previous poster said before condemming it though and measure the current again.

James.

Reply to
James

Nope. The only thing (that I am aware of) that should be drawing power is the clock. Ahh, didn't understand previosuly that I am meant to basically remove the alternator electrically. Take it that's easy enough to do?

Chandy

Reply to
chandy

That was lucky! Disconnecting the battery is the right thing to do for now.

Try disconnecting the alternator first (after disconnecting the battery!) and see if that stops the current drain. I don't know your car's particular set-up, but usually an alternator either has a large plug with a retaining clip, or it has individual terminals with nuts holding the wires in place. The thickest wire will be connected to the battery +ve, so if its a bare connector, insulate it before you reconnect the battery and meter to check for the current drain. You don't want that wire touching bare metal because the smoke from your meter leads will be like nothing in comparison. :-((

To answer your previous post. The alternator is a three-phase device and there are six diodes in a bridge configuration which rectify the AC output of the stator coils. It's possible for any one of these diodes to fail short-circuit. This is what causes the alternator to draw current from the battery and also means that the alternator can still produce an output from the remaining diodes and appear to charge the battery OK.

Diodes are not supplied individually but come as a pack which costs a few pounds. You will probably need to take the alternator apart to replace them and if you're not confident about doing that, your best bet is to go to your local motor factors and obtain an exchange alternator. If the alternator is quite old it may need bearings and brushes anyway and at least an exchange one will come with some sort of guarantee.

One other thought. If it's not the alternator, fuse boxes in Escorts are notorious for causing all sorts of electrical problems.

Once again, good luck!

Reply to
Ian Edwards

Could be the diodes on the alternator allowing the current to pass through the windings, either that or if you feel brave, examine the fusebox for moisture. In your particular car, the fuseboxes tend to enjoy the sauce in their old age and could be rusting away internally, with a short circuit just bad enough to drain several amps from the battery. This is probably worth checking pretty sharpish as if there is, it will no doubt be generating a little heat.

Ta, G.

Reply to
G-Man

You need to buy the correct diode pack for the alternator from a motor factor etc, and it has solder connections which need a fairly meaty soldering iron - IMHO 50 watts minimum.

Reply to
Dave Plowman (News)

Nuts. It's nuts. Will be giving that a bash in a while.

I've now tested all the internal fusebox fuses and come up with nothing. There are three 'main' fuses (40-60A) in a small black box attached right by the battery +ve terminal but I can't get them out! Is there a knack to it or do I have to undo the bolts on the side of each? Wouldn't have thought so but they don't seem to be budging. The

60A one is on a think wire..would like to get that out of the way and see what happens.

diodes

Which is handy cause I can test things then re-connect and go for a drive to re-charge. Glad the weather's holding up though.

alternator.

anyway

Looks like the original one is still there so could be an idea.

Seems dry internally at least..and no rust on the fuses or strange changes when pulling them or putting them back.

The alternative of course is re-connect and drive round to the local garage with the Omega 2.2 auto with 50k on it that caught my eye earlier ;) "Why yes, my current car runs fine as you can see" *ahem*

Thanks again!

Chandy

Reply to
chandy

Probably the easiest solution! Seriously but, if you can afford it, replace the car. 1.3 Escorts of that age really are utterly horrible cars to do anything with, I must admit. I owned a Mk5 1.4 and it was nasty, purely due to the lack of PAS (not sure about yours). If you must have an Escort, 1.6+

16v LX's '97+ are the only real choices.

Ta, G.

Reply to
G-Man

** Soldering GUN **

Andy

Reply to
Nik&Andy

Yup. But be careful not to overheat things.

Reply to
Dave Plowman (News)

Well I'll just replace the whole unit I think if that is what it is..as suggested before it's likely to be a bit tired by now anyway.

One question though, if it is the alternator, wouldn't something on the dashboard have lit-up to tell me there was a problem? (assuming all the bulbs work that is).

Chandy

Reply to
chandy

Not necessarily, the battery light would only illuminate if there was a problem with the charging circuit (i.e the alternator wasn't charging the battery and powering the car and everything was working on the battery). With the diodes faulty, it just means once the car is stopped, the power from the battery drains back into the alternator as if it was a normal motor. Your ~2A load would suggest this is the case.

Ta, G.

Reply to
G-Man

Well if it is the alternator it's definitely old enough to warrant being replaced completely. One question though. If it's the alternator would I not have been getting warning lights coming on on the dash? (assuming all the bulbs work!)

Chandy

Reply to
chandy

So does that mean the alternator is continuously trying to spin in those circumstances?

Reply to
chandy

Well it is basically a motor, so I suppose it may be.

Ta, G.

Reply to
G-Man

No!

In simple terms, an alternator produces AC. One of the functions of the diode pack is to convert this to the DC that the battery needs. (The other is to act as a "non-return valve" when the alternator is stopped). This conversion function does not work in reverse, so the alternator will not run as a motor when powered by the battery through a failed diode pack.

This is totally different to the situation with a dynamo equipped car from the past however. The means of rectification (AC>DC conversion) used with a dynamo is called commutation. This process will work in reverse, as anyone old enough to have connected a dynamo (briefly!) to a battery will tell you.

HTH

Chris.

Reply to
Chris Whelan

Motors work on the simple rule of DC to power them, AC generated from them. If the diode pack has failed, then what's to say that the power isn't getting back into the motor windings, thus turning it back into a motor.

Ta, G.

Reply to
G-Man

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