Thread: Fix for Discovery battery drain

[QUOTE=RRT;3233371]Most interesting and checked the charger tonight when I put it on and viola,



So again tonight the voltage was just 12.4 which it was the other day as well. Here is the voltage chart for the last week

Attachment 191220

/QUOTE]

Well the continued charging and it appears with DeSulphanination (indavertantly though) and SLS disconnection may have worked altready as the charge was up this morning...

Screenshot_20240907_090527_Battery Monitor.jpg

The dip in voltage around 5.00am this morning is a bit disconcerting, what drew that voltage...?

Originally Posted by dutchviking

If you use your Disco everyday: no problem.

Originally Posted by dutchviking

If you live in a sunny place where temperatures will not fall under -15C: no problem.

BUT when you leave for a 2 week break you might find the battery of the Disco dead. Or when you use a Webasto heater to cope with the arctic temperatures that hit Norway for about 6 months AND make 2 short daily trips only - the battery needs all the charge it can get, no place for a nasty 300 mA constant drain.

But finally fixed it. You can read numerous treads about the well known 300 mA drain caused by the SLABS ECU. Problem is that this ECU is always connected to the battery via fuse 11 (30A) (standing in front of the fuse box check the label on the cover or count from right to left). I always wondered why the ABS modulator was making space invader sounds like woy-woy-woy-woy but this is because the SLABS ECU powers the ABS Pump/modulator. Removed the connector from the modulator, but 300 mA drain stayed. Pulled fuse 11 and bingo! drain reduced to 27 mA. You can even hear a soft click when a relay inside the SLABS ECU de-energizes.

Just imagine. The 100 Ah battery can produce (in theory) 100 Amperes for one hour. A drain of 300 mAh means it will take 333 hours before the battery is dead. However to crank a Td5 you need at least 60-80 amperes for a couple of seconds. This means that (in my case) not using the car for 2 weeks, or in harsh winter conditions like we have here with -20 C for a number of days, short trips AND the extra 300 mA drain cause problems.

To keep a long story short, pin 2 (C0504 which is the biggest connector on the ECU, 2nd seen from bulkhead) receives 12V through the ignition lock. I use this connection to energize a relay (taking the ground from pin 12 of same connector). The power supply for the SLABS ECU via fuse 11 is now running via the relay contacts to pin 1 of same connector. Meaning: no key no drain.

The Self Leveling function inside the same ECU still works, so after shutting the engine and removing the key and locking the car the ECU still lowers the rear suspension a bit as usual.

<Edit> I was wrong with the SLS statement directly above. When you come to a full stop i.e. reached your destination you have to give the SLS 10 seconds to lower the rear springs. If you stop and immediately remove the key the springs keep sittin' where they are.

This MUST be one of the reasons to keep the SLABS ECU under power at all times. But for a turbo engine it won't harm having it spin down before you remove the key, so still consider this to be a fix. </Edit>

I am now free from this annoying drain that has been there since 2004 when I bought the car. No worries about safety, the relay is an original LR item and prone to the same MTBF as all the other relays in the car, and the ECU does so many checks that any problem in the system will be detected.

Images show how easy the process is, takes about 30 minutes.

Hello dutchviking, I hope you can reply to this message, which is over 10 years old!

First of all, did you encounter any problems after installing the relay to power the panels?

And how exactly did you do it? Did you cut wires 12 and 2 to connect them to the relay? Or did you connect relay wires 85/86 in parallel with wires 12 and 2?

Thank you in advance for your reply.