discharge

This sounds to me like the alternator diode has gone - what that does is stop current flow reversal so the current from the alternator goes to the battery and stops there.

If the diode goes down, the alternator will still throw out a charge whilst running but when the vehicle is idle, the current flow reverses from the battery back to the alternator turning the alternator windings into a giant electromagnet of sorts - this removes charge from the battery sufficiently for it to go down in 24 hours to a difficult start and within 48 hours generally to a completely flat battery.

It is possible for the alternator to be throwing out its normal charge this giving you a healthy voltage reading and still have the fault above.

The 2,5 year old battery of my Disco 1 300TDi ('98, ±60 k miles) is slowly discharging. After a day in the garage I have difficulty starting it. I assume the battery is OK (can't test it myself). I charged it using a trickle charger, left it over (freezing) night and measured 12.7 V next morning.

When I put a multimeter across the battery terminals the display reads

So, my question is, how do I go about finding the culprit? After or when measuring amps for a second time (0.02 amps?!) my multimeter died. I will be going to town this afternoon to by me a new one, but I would like to hold on to that one a little while longer, so I welcome any advice you can give me. For instance, can I remove fuses to measure amps across the fuse terminals? Will this tell me anything?

As you may have noticed, car electrics is not my forte, and that's putting it mildly. But I'd rather find the leaky bugger myself than have the dealer look for it for two days (and charge me accordingly).

Thanks, Richard

I disconnect the battery + and put a headlight bulb accross between the battery lead and the battery +, the bulb lights when there is a draw from the battery and goes out when the draw is disconnected it's easier to see than a meter. With a smaller current draw I use a smaller bulb then pull fuses out and disconnect stuff, though as someone said it could be the alternator. I once did a car with a 15a draw, the heated rear window relay was stuck on.

-- Jon

Quite an effective test method but safer if you put the bulb between the

-ve battery terminal and lead rather than +ve - it doesn't matter then if the circuit accidentally shorts to the metalwork of the vehicle. Just a suggestion :-)

Thanks all, so far.

I will save the expensive type operations for last, so I think I will start with my brand new multimeter, or a bulb (good thinking) between the -ve terminal and lead (just to be on the safe side), and disconnect the alternator and Webasto first, followed by all the fuses I can find.

If I still can't find anything, I will take the alternator to the shop to have the diode thingies checked, and the rest, while there at it.

Will keep you posted.

Regards, Richard

Steve:

When pulling fuses you need to pull them one at a time and replace the last one before removing the next because so many circuits use more than

Make a record of the current drain for each removed fuse and use that to short-list the potential problem circuits.

Thanks Steve,

I've made a nice spreadsheet, based on the wiring diagrams in the Haynes manual. Give it a go tomorrow.

Regards, Richard

SteveG:

Well, turns out to be the alternator, like David suggested. Removing the 6 'easy' fuses in the engine bay made no difference, but when I disconnected the 100 amps fuse, the current drain dropped from a whooping 1,85 to a more acceptable 0,02 amps. Looks like the current drain will turn into a cash drain come monday. Even a reconditioned one will set me back something like 350 euros (250 pounds?). Still, I'm glad I found it. Thanks for your help.

Regards, Richard

Richard:

Only if the alternator is the *only* thing the other side of that fuse, ie the "feed" from the alternator doesn't split off elsewhere via another fuse elsewhere. I'd unplug the alternator whilst monitoring the current drain just to make sure.

Remember most DVMs have and need a fuse to prevent against over current. So unless you know roughly what the max current is this can blow. Some vehicles will take a fairly large load when connecting the battery first which then settles down to the quiescent amount. And on my Fluke DVM this fuse costs an arm and a leg. ;-)

A good auto electrician should be able to replace the diode pack if you remove the alternator first. It can be done at home but usually requires a meaty soldering iron. The last one I bought cost about 30 quid - roughly the same as a regulator.

But have you shopped around for exchange units? They don't have to be genuine OEM - respected makers like Quinton Hazel and others do them. Try a good motor factor. I recently paid under 60 quid for the 75 amp unit fitted to my SD1.

On or around Sat, 27 Oct 2007 16:10:28 +0100, "Dave Plowman (News)" enlightened us thusly:

good point, but it'll be a 100A one on the 300 TDi, probably. You can still get 'em cheaper than LR want though, especially as LR ones are service-exchange too.

last one I got came form partco, I think. Mind, it made the rev counter read wrong...

Thanks, I'll be sure to check the current drain again when I take the alternator out to have it reconditioned.

Regards, Richard

"Dave Liquorice"

I got a quote from a car parts dealer over here, Brezan, for a recon alternator: 360 euros (GBP is about 1,40 EUR). Dealers and recon shop were closed for the weekend. VIN says I need AMR5425, 100 Amps. Rimmer charge 570 euros (exchange surcharge included)

Dave Plowman (News):

Pattern part.....which means no more, I think, than it is obtained through other than Land Rover channels. It may be the same part as used by Land Rover or may be some other manufacturer's 'equivalent'.

I do it before taking it out just in case that extra 1. amps isn't going through the alternator... Each to their own though.

I *think* they are usually re-claimed reconditioned units. I don't think the likes of Quinton Hazel make them new. Although in the past some different mainstream makers made identical units.