1994 Discovery alternator/regulator

Disconnect the battery overnight and see if it starts in the morning and if so then use a suitable ammeter between the disconnected lead and the battery terminal to see if any current is passing (leaking) whilst engine is stopped. Try it with the alternator disconnected also to see if that stops it. All this with the engine stopped of course.

Martin

Having looked at things like this on my '95 ...

When left in the acc' position there is about 600mA being pulled out of the battery, that is without a radio and interior lights off !!

Just sitting there with key off and measuring the current through the alternator fuse it was 120mA.... I check the 87 RR and the orginal alternator was pulling 60mAs and the secondary ( 120A Japanese ) was pulling less than 20mA.

All these alternators where able to supply good loads at idle .....

Hope that is of some help...

Max

redseadiver wrote:

On or around Thu, 18 Oct 2007 00:46:24 +0100, "Oily" enlightened us thusly:

that's about it. it's got to be either a leak or a fscked battery. If the battery is more than about 3 years old, it could be self-discharging.

if the battery is in good nick then you're looking for something like about half an amp, which is quite a lot for a leak.

The most usual cause of quick battery discharge with everything switched off is a faulty diode in the alternator rectifier pack. The alternator is connected across the battery at all times but the diodes stop current flowing from the battery into the alternator but allow it the other way - obviously - to charge it. So a form of one way valve. A failed one goes short circuit and only makes a marginal difference to the alternator performance. But draws about 6 amps from the battery with the engine stationary.

You can check this by disconnecting the alternator output lead - the thick one(s). If the battery then survives a few days you've got the answer. Alternately insert an ammeter capable of reading about 20 amps or so between the output lead and alternator terminal. Or a stop light bulb which will light up brightly with the fault present.

Not the old favourite that no one else has mentioned of the remote door locking system(*1) being constantly woken up by something else on the same frequency? "Something else" being anything from a wireless burglar alarm to a wireless weather station.

It's just got cold(*2) and one thing that car batteries don't like is the cold. Had one die on me overnight when it got cold about this time of year a while back, battery was only about 3 years old. Went from no problems swinging the engine and starting to really struggling in 24hrs and a frost.

First thing I'd do is monitor the current drain with the vehicle in the "off" state. You might have to wait a few minutes after switching "off" for everything to fall properly asleep. If that only showed a few tens of mA drain I'd get the battery tested if that indicated OK (doubtful if it's been flattened a few times car batteries don't like that either) then I'd start looking at the charging/alternator side of things.

(*1) Assuming a '94 Disco has such a feature...

(*2) 'Tis getting nippy the gritter has been past twice this evening already.

You've got some good advice on testing and tracing any potential fault in other threads but just so you know you can replace the rectifier pack on the alternator ~ it shouldn't cost more than a few pounds. You don't even need to remove the alternator to do the job :-)

Are you sure it's easy? The regulator usually is - but the diode pack is normally soldered and would be very awkward to do without removing the alternator. Last one I bought cost about 30 quid.

Thanks to everyone for their advice. Have copied it all down ready for an onslaught on it tomorrow Saturday. Will let you know how I get on. Have checked the price this afternoon for the pack referred to and have been told the unit is £52 inc VAT. Have a good weekend everyone.

If you do the checks and discover it is the alternator drawing current I'd price up a 'Joe Bloggs' re-con from a decent motor factor. They're often cheaper than buying the bits to overhaul one - and come with a warranty.

I had our local vehicle electrician replace mine ... 20 mins .. 2 burned =

fingers (he didn't wait for the engine to cool down) ... =A330 incl vat.

--=20 Regards

Steve G