SLK 230 Residual Current (Ignition Off)

[mbportcul1s]

Can anyone tell what the residual current should be on a 1998 SLK 230 with ignition turned off. I assume it is only the cars security alarm system that should be drawing any current in this state. The battery on my wifes car is drawing about 190 mA and when the car is not used for about 3 days, the battery (only 12 months old) becomes discharged.

 

[Dec]

No idea but that’s way too high, check your alarm, lock yourself inside the car, stay completely still for 60 seconds then open a door to see if the alarm sounds ok.

Dec

 

[television]

45 to 55 ma max.

The easiest way is to leave a clamp meter or meter in series with the battery and pull each fuse 1 by 1 till you find the one that is pulling the excessive current. It may not be a fused item and a CAN bus not sleeping.

Try the fuses first including the boot fuse box and we can take it from there.

There is an article in the DIY on solving some of these faults

 

[Alex Crow]

Above comments and advice seconded here.

190ma should not drain your battery in 3 days however, it ought to last up to a fortnight at that rate.
Also, how long are you giving the car to sleep before the test? Can be up to 1/2 hr with some models before it drops right down.
Is it being done with the car locked and everything closed?

 

[mbportcul1s]

SLK 230 Residual Current

I am fully charging the battery and then connecting a 10A meter between ground and the negative post. The initial current starts at about 400 mA but then settles down to 190 Ma after about 30 secs. I haven't left it connected for longer than this period but will leave the meter in situ and see what the reading is after an hour. The DIY section has an article on MBs in general but says that the possible problem with the CAN Bus staying partially active and causing a drain was only a problem on 2000 models onwards so I am guessing a 1998 car would not experience this problem.

 

[television]

If you do not have comand in the car there is not much in the way of any wake up in the 170,,, I know that 200ma will cream off the top off the battery in a few days.

It correct what you are doing and I am sure that you do have a leak somewhere, have you tried pulling the fuses 1 by 1 to see

 

[Alex Crow]

As you have realised, 30 seconds is far too short a time.

Please let us know what you measure after 1/2 hr.

 

[television]

As you have realised, 30 seconds is far too short a time.

Please let us know what you measure after 1/2 hr.

Well they never go up really do they Alex, I have never seen one go up, circuits are shutting down and nothing can start up without the key turned.

He has already said it falls to about 190 in 30 seconds, not that the meter was checked for 30 seconds.

 

[Alex Crow]

Actually Malcolm, in post #5 he does specifically state that he has not tested beyond 30 secs.

I would personally want to see it after 30 mins myself - yes, they do not usually go up again, but nor do they drop down fully in 30 secs...

 

[mbportcul1s]

SLK 230 Residual Current Drain

Gentlemen,

My thanks for all your replies. The state so far - I have left the meter connected (to a fully charged battery) for over an hour. The current settles down to about 80 mA after about 15 mins and seems to stay at that level, at that level I assume it would take several weeks of non-use before any significant drain on the battery would affect starting. So am I probably pursuing a premature battery failure (an Exide which is less than a year old)?

 

[television]

80 ma is still on the high side, or higher than it should be, some batteries can fail in the cold weather, just loosing their charge when a cell goes high resistance. 45ma is the figure to aim for as 80 is almost double. Have you tried pulling the fuses 1 by 1, the doors in the front and PSE pump in the rear boxes

 

[mbportcul1s]

SLK 230 Residual Current Problem

No, not yet, this will be the next procedure to try and eliminate the possibility of battery failure. I suppose I could get my local garage to do a discharge test to see if the battery is a possibility. Will update the forum when I get some results.

 

[television]

No, not yet, this will be the next procedure to try and eliminate the possibility of battery failure. I suppose I could get my local garage to do a discharge test to see if the battery is a possibility. Will update the forum when I get some results.

It depends on the tester,,, I do know that the actual Exide battery depots do have a good tester that diagnosed mine when it did the same thing