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Discussion Starter #1
Like many people I guess my MINI was left for a few days over the xmas period and suffered a flat battery.


My car has the alarm and minidisc player and was built
mid Novemeber

Also like many others the car had unlocked itself
before the battery died. My guess is that this is a failsafe
mechanism to allow access to a dead car.

Seeing as it took The emergency service people 8 hours
to come out I decided to take matters into my own hands,
removed the battery and gave it a good charge.

Once the battery was re-installed I decided to measure
the residual current drawn from the battery using my ammeter
(which can go up to 20A)

Seeing as I saw 13A momentarily when the car is locked,
then you would blow the fuse doing this on most ammeters.
There is an easy way around though which I shall describe in
a minute.


Observations


1) ECU seems to shut down after a couple of minutes (NOT 16)
but then goes through a continuous cycle of shutting down
and waking up.


Current sequence is approx

1) 0.9A for 1 minute
2) 0.8A for 30 seconds
3) 0.7A for 1 minute
4) 0.2A for 1 minute 30 seconds

and so on. It was still following the sequence an hour
after the car was locked up.

This averages to about 400mA, which would flatten the battery in 4-5 days


My guess is that the once the ECU shuts down, the spurious
c-bus pulse from the radio wakes it up. It then goes away
and thinks about something (like why its been woken up),
and then goes to sleep again, only to be woken up later
on.


If I removed fuse F27 (the radio) then the current
settles pretty quickly to a constant 20mA. If your car does not have the alarm, it will be lower than that.
This would be a little higher if you have a fixed
radio fitted, but I would expect to see no more than
50-100mA

You can make these measurements yourself if you have
and ammeter that can read up to 1A

1) Disconnect the battery -ve cable.
2) Use some 20A automotive wire to bridge the connection
3) Connect up the ammeter between the -ve cable and the
-ve terminal of the bettery
4) lock the car
5) remove bridge cable (with ammeter still connected)
6) observe current
7) reconnect bridge cable (or risk blowing ammeter fuse)
and unlock car -
8) remove F27 (2nd radio fuse)
9) repeat above procedure for measurements

WARNING - if the ammeter becomes un-connected
while the car is locked and you have the alarm, it
will go off. It can only be stopped if you reconnect the
battery cable and unlock the car.


So until you get your new radio fitted, you can remove this fuse to avoid a flat battery.

Incedently, my fuel consumption has now improved by 3-4mpg
now the alternator is not constantly having the charge the battery.
 

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space_cadet said:
Like many people I guess my MINI was left for a few days over the xmas period and suffered a flat battery.


My car has the alarm and minidisc player and was built
mid Novemeber

Also like many others the car had unlocked itself
before the battery died. My guess is that this is a failsafe
mechanism to allow access to a dead car.

Seeing as it took The emergency service people 8 hours
to come out I decided to take matters into my own hands,
removed the battery and gave it a good charge.

Once the battery was re-installed I decided to measure
the residual current drawn from the battery using my ammeter
(which can go up to 20A)

Seeing as I saw 13A momentarily when the car is locked,
then you would blow the fuse doing this on most ammeters.
There is an easy way around though which I shall describe in
a minute.


Observations


1) ECU seems to shut down after a couple of minutes (NOT 16)
but then goes through a continuous cycle of shutting down
and waking up.


Current sequence is approx

1) 0.9A for 1 minute
2) 0.8A for 30 seconds
3) 0.7A for 1 minute
4) 0.2A for 1 minute 30 seconds

and so on. It was still following the sequence an hour
after the car was locked up.

This averages to about 400mA, which would flatten the battery in 4-5 days


My guess is that the once the ECU shuts down, the spurious
c-bus pulse from the radio wakes it up. It then goes away
and thinks about something (like why its been woken up),
and then goes to sleep again, only to be woken up later
on.


If I removed fuse F27 (the radio) then the current
settles pretty quickly to a constant 20mA. If your car does not have the alarm, it will be lower than that.
This would be a little higher if you have a fixed
radio fitted, but I would expect to see no more than
50-100mA

You can make these measurements yourself if you have
and ammeter that can read up to 1A

1) Disconnect the battery -ve cable.
2) Use some 20A automotive wire to bridge the connection
3) Connect up the ammeter between the -ve cable and the
-ve terminal of the bettery
4) lock the car
5) remove bridge cable (with ammeter still connected)
6) observe current
7) reconnect bridge cable (or risk blowing ammeter fuse)
and unlock car -
8) remove F27 (2nd radio fuse)
9) repeat above procedure for measurements

WARNING - if the ammeter becomes un-connected
while the car is locked and you have the alarm, it
will go off. It can only be stopped if you reconnect the
battery cable and unlock the car.


So until you get your new radio fitted, you can remove this fuse to avoid a flat battery.

Incedently, my fuel consumption has now improved by 3-4mpg
now the alternator is not constantly having the charge the battery.
Children should be under supervision of an adult whilst undertaking this of course.

Seriously though, thats the most amazing and informative post I have read here so far. Well Done. Can you tell me; when is a current described as "dark" ?.

And secondly, have you informed BMW of these quite amazing facts and figures. I think you should, coz they obviously can't figure out the problem for themselves, except to put a different battery in the car, as appears to be the case on other threads on the subject.
 

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Re: Re: dark current measurements and dodgy radios

Basil said:

...except to put a different battery in the car, as appears to be the case on other threads on the subject.
Mine was fixed by changing the MiniDisc unit but not the battery. It was also left for 2 days outdoors over Christmas and then started 1st time. On the one occasion the battery was flattened, the windows and doors stayed put (thankfully). Seems like another case of 'random build qualityitis' going on here..:(
 

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Re: Re: Re: dark current measurements and dodgy radios

Dogger said:


Mine was fixed by changing the MiniDisc unit but not the battery. It was also left for 2 days outdoors over Christmas and then started 1st time. On the one occasion the battery was flattened, the windows and doors stayed put (thankfully). Seems like another case of 'random build qualityitis' going on here..:(
Hmmm, not too random it seems. (Shouldn't start on this.....my apologise)
 

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My CD BOOST was replaced by the dealer.

Original unit was drawing too much power and would have drained the battery if left long enough.

New unit (looks exactly the same) does not do this.

So check with your dealer for a replacement.

Dave
 

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Do you reckon that fitting an aftermarket radio would solve this?

Jon
 

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A few weeks ago, I started a thread explaining how to tell if there is current drain when the car is shut off without having to remove the battery cable. All you need to do is measure the voltage drop across the negative battery cable with a millivolt meter. Most DMMs have an "mV" range and 300mV or less should do fine. On my old Datsun, I get a reading of "0" with everything off and a reading of .8mV when the interior light is on. Obviously using an ammeter in series will give you more accurate readings, but Apial tried it at my suggestion and blew out the fuse in his meter.

The botom line is, the current drain on standby should only be a few milliamps at most, just enough to hold the memory for the radio and power the alarm. Look at the small battery in your computer. It will hold the CMOS settings for years, so you shouldn't need several amps to keep the ECU settings intact.
 

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jonathan_king said:
Do you reckon that fitting an aftermarket radio would solve this?

But why should you have fit an after market Radio to solve this problem,christ I'm starting to sound like "Mr Bill":D
 
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