Question: What is an R230 consumer battery's normal current load when parked and dark?

I've searched around here and elsewhere - and while I find a lot of discussion of the dual battery system in general and the consumer battery in particular, So far I have not been able to find any well sourced value for the correct and normal amount of residual current load on the consumer battery when the car is parked and dark. (i.e. no lights, no doors open, no buzzers, beepers, pumps, etc.) This would seem to be a very predictable number, as well as very easy to measure. Alas, no one seems to have yet posted it in a way that I can find it. I have tried...o.k? :-) Maybe I missed it? I looked at all the MB factory documentation I could find so far...and nothing definite appears.

I have a more than passing familiarity with this electrical system, and electrical and electronics in general. Using professional tools at my disposal, my car seems to be drawing just a hair under 3 amps after settling down and fully resting (with trunk open and therefore a ~10W trunk lamp illuminated) So, eliminating that trunk lamp, that's still around 2 amps going somewhere...but where? That figure seems VERY high to me, and the rate of drain of my AGM consumer battery is correspondingly high as well.

To be clear, I'm not looking for "fixes" like trickle chargers, etc. I'm just looking for the correct factory value. Does anyone happen to know what the factory figure is for consumer battery load when an '06ish R230 is parked and dark and operating as designed?

Thank you very much in advance!

coolblueglow

 

The value should be in 10's of milliamps, sorry no exact value.

However you must close the boot (trunk) lid and lock the car to get any meaningful readings, as car will not go to sleep otherwise.

I am currently (pun intended) playing around with a 20 A Bluetooth DMM, which i can lock in the boot, and read on my phone, and will be setting it up as a data logger to a laptop so I can get longer readings over night etc..

I currently monitor both front and rear battery voltages (With data loggers), and State of charge, (though not sure how this is calculated) so I can see the function of the BCM

Only just started so waiting for some results over next few days of use.

 

Thanks for that,

Yes, agreed. It would seem sensible that the reading should be in the tens or perhaps a hundred or so mA. But based on pure old paper calculations that just cannot be what's happening on my car - at least right now. The hard part is not knowing. I have 1 system fault generating a red battery warning, but the charging and battery system numbers look o.k. by direct observation, except that weirdly high discharge rate. Could be my measuring technique, could be normal, could be something broken in the BCM or some system stuck "on" like the fellow with an old Nokia phone charger cradle that was stuck on and bleeding out a bunch of power that way. But whatever it may be, there is no way a system load in the tens of milliamps is going to drain to dead a Group 48 sized AGM battery in a week, and that's what I have happening and see happening for a lot of people. The bandaid is "trickle charger"...but I don't really love that idea for a variety of reasons.

And, based on the number of people I hear complaining about consumer battery drain down, either the normal load is more than a few tens of milliamps, or people are doing something fundamentally wrong in how they park and leave their car...or there are a lot of mildly broken R230 electrical systems?

Love your idea of a DMM datalogger. Very high tech. As far as monitoring, I'm taking a more brute force approach. I call it "wire", along with an HP ammeter and a pencil and pad. :-) I do admire your pluck in getting automatically aggregated datalogs of load over time, though! One would think with all the myriad of monitoring systems on this car, one could simply call up the discharge rates on the various systems with relative ease. I suppose if I had DAS, it might?

The more I learn about the BCM and the dual battery system, the more skeptical I become about this automobile's future in my garage.

Anyway, thanks for the reply! Anyone else have a for sure number?

 

A recent discussion mentioned 40 - 80mA. But that's just hearsay. I haven't read of a definitive value.

But it's also what you might expect from the quiescent current keeping various modules in standby. Probably more towards 40 than 80. The boot light alone is drawing 830 mA if it's 10W, but that's before the car goes to sleep.

Do you have a DC mA meter with peak hold you can connect up overnight?

The alarm siren is a known current drain; pull the brown 7.5A fuse in one of the under-bonnet SAMs to eliminate it.

 

Official spec from MB is anything less than 50mA is acceptable.

 

So taking the brute force method, I rigged up a proper current measuring fixture to the thing, complete with closed trunk and locked doors and all...and then just monitored it.

Turns out on my car at least;

1. My 06 R230 is not parked and dark in the true sense of the word until the doors are LOCKED. With it locked, my consumer battery draw quickly goes so low that I cannot get a reliable measurement. Car is NOT drawing detectable current on my fixture (with a minimum resolution of 10mA) Thus, no more than 9mA coming off the battery when locked.

2. BUT...UNLOCKED the car just does not settle, even though it eventually does drop way lower. But left unlocked, after sort of settling down, I still get 10mV loads that drift in and out, with regular twitches and spikes and "check this/check that" things going on somewhere in the brain of the beast. It never really settles down, at least not for the first hour. Sometimes it seems like it is going to settle and then "Huh? what?..." and there is a little current spike and then it goes back to 10mA for a while and then less and then twitches again. Weird, but there seems to be a discharge difference between locked and unlocked states.


CONCLUSION: I now know that I'm just not in the MBWorld forum's inner circle. You know, the official "You are a true Mercedes Benz insider" or maybe I don't know the secret handshke or something? I suspect you guys have secretly been laughing all this time and saying "should we tell him? NAAAhhhh... he's a newb to the forum...lets see if he figures it out!"

Gee...why didn't you guys tell me?

Lock the car for better consumer battery life

I feel kind of hurt.

 

Aw, well, g0rsq did actually mention that, in post #2: However you must close the boot (trunk) lid and lock the car to get any meaningful readings, as car will not go to sleep otherwise.

 

Hi Tom,

Yeah, I saw that when he said it. I was just kind of kidding around. :-)

At least I know now to LOCK the car. My wife is ecstatic. She's always on me to lock the car, even in the garage. I had to tell her she was right. :-)

 

For the fun of it and to be able to check draw on my rear battery I bought a TRMS inductive amp meter. Cheap, a claimed 2% accuracy, DIY stuff.
In stage 7 (float) the cTek draws 22 to 29 mAmps from the mains 230 VAC (5,1 - 6,7 watts).
At the same time, DC current to the battery constantly fluctuates between 41 and 128 mAmps (I did not check the voltage there but I presume 13,6 V).
I was told contactless measuring of low currents is not that reliable.

 

Interesting.
So with my fixture - using an o.k./decent DVM ammeter set up in series in order to directly measure current flow - I see NOTHING over 9mA after the car settles. This particular meter resolution stops at 10mA in this range, and claims to be a 2% accurate meter. I do see settling spikes and the stage-down of current demand in the first few minutes after locking the car. After that, I watched steadily for 15 minutes and intermittently after that for an hour and I see zero current flowing. So it is possible that up to 9mA +/- 2% could be flowing and my meter simply wouldn't see it. But I am definitely not seeing 40mA, ever (with the car locked, the console, glovebox and boot closed)

Anyway, I'm working on an idea for a fixture to allow me to switch to the milliampere range of my really nice HP 3465A bench meter. It is extremely sensitive and accurate down to the uA range...but of course the car has to settle below 200ma before I can connect this particular device in series. Therefore, I'll probably have to build a precision shunt to make this measurement work. I don't think I have one at this ratio right now, but I have the parts and the calibration gear to build it. I guess I'm just lazy, even though I shunt be. (haha, see what I did there?)

I will be more confident in declaring my car's real current drain after measuring it with a real precision instrument.

 

Looking at your car from a different angle, one might consider to just fire her up and drive it like you stole it.

 

Ha! Yeah,
Actually we were scheduled for a run up to Kansas City in the silver bullet, but a crisis in our friends' world intervened and we had to postpone.

Good thing. That AGM battery died on the Wednesday right about when we would have been driving. We would have been stuck on the road with a flat dead AGM and a red battery warning and a 'go to workshop' on the display!

THAT is why I don't just "drive it like I stole it", as you say. I know a lot of people who get away with that, but every time I try it, that I get "caught by the authorities" :-)

Cheers,

Keith

 

Keith, thanks for this thread, just locket my car in the garage. I don’t lie trickle charges either. I made a promise to drive it like I stole it more frequently

 

Anyway, I'm working on an idea for a fixture to allow me to switch to the milliampere range of my really nice HP 3465A bench meter. It is extremely sensitive and accurate down to the uA range...but of course the car has to settle below 200ma before I can connect this particular device in series. Therefore, I'll probably have to build a precision shunt to make this measurement work. I don't think I have one at this ratio right now, but I have the parts and the calibration gear to build it. I guess I'm just lazy, even though I shunt be. (haha, see what I did there?)
I will be more confident in declaring my car's real current drain after measuring it with a real precision instrument.

Post back the results. I was going to measure mine, but if you get there first, so be it!

9 mA sounds much more like what I'd expect to measure. I wonder how many owners complained of current drain and replaced batteries, without keeping the car locked? Me included, which was why I fitted an isolator on the battery, but that is mainly for working on the car and to avoid the BCM catching fire while it's parked (a rare, but known possible fault).