I'm fitting a Battery Brain to prevent the battery from dropping below 11.8V
I've tested most of the fuses 20-mins after locking, replaced the Final Stage Resistor, fitted a new Bosch S5 battery, tried removing the Nav, blower, and headlamp washer fuses (#12, #28, #49), but it is still losing current.
The Battery Brain seems the best option to ensure I can start the car after a few days.

The device needs a connection to a wire that is ON when the ignition is on, and OFF when the ignition is off.

1. Can you suggest a suitable wire? I'm thinking there might be some wiring to the LPG ecu which might fit the bill.

2. Is there some wiring to a fuse in the passenger compartment fuse box that I could tap? How difficult is it to access from the engine compartment?

Or, are there any other fuses I should pull to fix the battery drain? My tester doesn't seem to fit in the bottom row of fuses, so I haven't tested them properly...

Any help very much appreciated.

Last edited by user58101 on 13th Dec 2012 3:38pm. Edited 1 time in total

Have you considered a battery drain back thro the alternator when the car is not being used?

I haven't tested for a battery drain back to the alternator when the car is switched off.
I'll take a look at how to test that.
Thanks

Does this (battery Brain) only kick in after all the systems (e.g. DVD / Airbags) have shut down? .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999

The Battery Brain only kicks in if it finds that the battery voltage has dropped below 11.8V.
When you come to use the car, you can re-connect the battery by pressing a button on a Battery Brain remote control, or by pressing a button on the device which is mounted near the battery*.

The wire that I need help connecting is to stop the Battery Brain from disconnecting the battery if the ignition is switched on and the voltage happened to drop below 11.8V.


*this is according to the instructions - obviously I haven't fitted it yet!

Battery drain back thro the alternator starts as soon as the alternator stops rotating. It will occur in addition to any other current drains that may be present irrespective of the "sleep" condition of the car.

Correct me if I'm wrong.
After the ignition has been switched off, it take the car a period of time to shut down.
If the battery voltage is below your 11.8v at the time of turning the ignition off, then your battery brain kicks in and turns the battery power off, the system will shut down prematurely.
Surely this will upset the vehicle electronics.
Just a thought. '88 RR Classic, '90 Classic, '93 Classic, '02 Discovery TD5, '55 Discovery 3, '01 P38 4.6, '06 L322 Vogue TD6, 2012 L322 Vogue TDV8, 2017 L405 Autobiography
Wife. '01 Freelander, '07 Freelander 2.

Roger 47 - I think you're correct. However, this is unlikely to happen after driving the car.
It could feasibly happen if I unlocked and locked the car (e.g. if I just went to get something out of the boot). But in this instance, it is likely that the voltage would be the same before and after me doing this. i.e. if it was above 11.8V beforehand it would be above it afterwards; if it was below 11.8V the Battery Brain would have already kicked in and I wouln't reactivate the battery if I was just getting something out of the car.

Hope my thinking is clear, it's slightly complicated to describe...

nicedayforit - I will try to find the relevant leads to disconnect to monitor any alternator current drain. I might need to invest in a DC Clamp Ammeter.

I agree abrownson if you have a good battery and an alternator delivering the correct output.
However, if by some kwirk you don't, the repercussions, as I am lead to believe could be expensive.
Not sure if I would take that chance.
I plug my RR into a battery conditioner as approved by a main dealer, as I don't us it every day.
However, I think your best bet is to find the cause of your problem.
Good luck. '88 RR Classic, '90 Classic, '93 Classic, '02 Discovery TD5, '55 Discovery 3, '01 P38 4.6, '06 L322 Vogue TD6, 2012 L322 Vogue TDV8, 2017 L405 Autobiography
Wife. '01 Freelander, '07 Freelander 2.

If you have 11.8V on shutting down the ignition you have serious problems.
It's more likely the battery voltage will be in the order 12.6V to 12.8V which will gradually decay over a number of hours to 12.6V, it will then drop further depending on any battery drain.
On a good battery it could take a day or more.
I wouldn't really expect the battery to drain to 11.8V for a few days depending on the fault.
I'm not sure you could start the engine with 11.8V, particularly in winter, wouldn't start a TD6.
You don't need much of an ammeter to measure battery drain it should only be in the order of 0.3-0.4A maximum.
Anything else and you would have a flat battery every morning sufficient to be unable to start the car.
To measure the alternator drain you just need undo the large cable on the alternator and connect the ammeter to the cable end and the terminal on the alternator respectively you just took the cable off.
Be careful the alternator cable is at battery voltage 12V so don't let it touch metalwork.
Depending on you ammeter it should be possible to cobble something together with bits of wire and connectors.
I assume you don't have the 12V jump post as per the TD6. It's easier to check battery drain on a TD6.

Quote:

It's easier to check battery drain on a TD6.

Go on.............. .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999

To continue...

If you wish to measure possible battery drain current to alternator on any RR that is fitted with a +ve jump start post, be it TD6 or V8, you do the following.

Switch off the ignition and close all the car doors, leave the car for about 30min to allow everything to go to sleep.

Disconnect the +ve thick red cable from the engine side of the jump post.
Connect your ammeter (that has a range upto about 3A) between the jump post and the end of the red cable you have just disconnected from it.
Your ammeter will then read the current drain from the battery to the alternator.
In a perfect world the current should be zero but a few mA isn't going to cause a serious problem.

Note, the cable you have connected to also supplies the starter motor but it is extremely unlikely there will be any current drain to the starter.

If you wish to determine the total battery drain current on any RR you do the following,

Switch off the ignition and close all the car doors, leave the car for about 30min to allow everything to go to sleep.

Disconnect the -ve thick brown cable from its connection to the car body adjacent to the battery.
Connect your ammeter (that has a range upto about 3A) between the earth stud on the top of the wing and the end of the cable brown cable previously disconnected.
Your ammeter will now read the total current drain from the battery to car.

If you do both of the above, subtracting the alternator drain current from the total drain current will give you the current drain to the cars "systems".

Thanks NDFI

I must be being dumb today.....

Quote:

Disconnect the +ve thick red cable from the engine side of the jump post.
Connect your ammeter (that has a range upto about 3A) between the jump post and the end of the red cable you have just disconnected from it.

Can't see how this would make a circuit? If you mean item 6 on image below?

Click image to enlarge

 .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999

No not the battery side of the jump post, the cable on other side of the panel that drops down to the starter / alternator.
I just find it easier to disconnect this cable as the cable when disconnected is dead but the jump post bolt, which is live, is fixed in place and not likely to touch any metalwork. Less sparks
The circuit is made by the alternator being grounded to earth by its mountings and the ammeter.
ie the alternator is connected to the -ve post on the battery.

So, you mean remove cable (1) from jump post (2) then connect ammeter between (1) and (2) ?

 .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999