Intermittent Battery Drain - Very Annoying! - Mercedes-Benz Forum
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post #1 of 21 (permalink) Old 01-09-2011, 08:45 AM Thread Starter
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Intermittent Battery Drain - Very Annoying!

I searched for battery drain problems and, although there are some threads, nobody posted how their problem was fixed. I reckon that if people post for help, they should do the decent thing and report how their problem was resolved.

That's the whingeing Pom bit out of the way and here's my problem. At the beginning of December when we had snow and very low overnight temperatures (for Wimbledon) my battery went flat. I recharged it and 3 nights later it went flat again. So I got a jump start and drove to the battery shop (Halfords) - my battery was 2.5 years into a 3 year warranty. The guy tested it - OK; he tested the alternator - OK; he tested the battery again - bad!; he tested it 6 more times - all OK. Without any prompting he fitted a new replacement battery - which I thought was pretty decent - but said that it might not be my problem. I said 'yeah, right' and drove home. 2 weeks later during the second bout of low temperatures, my new battery went flat over a 24 hour period.

So I recharged it and re-installed it with an ammeter in series with the ground connection. The drain - doors closed, trunk light off - was 30 mA - and 40 mA when locked with the alarm on. So, no problem for a 100 Ah battery and obviously the reason why I've been able, in the past, to leave the car for 3 weeks at an airport with immediate start on my return.

Christmas Eve I used the car and checked the leakage current when I got back. This time it was 2.9 A and here was my problem. I then pulled and replaced every fuse in the trunk without making any significant difference to the current, and then every fuse under the bonnet/hood - nothing.

But with my head stuck under the hood at 8 o'clock at night on Christmas Eve, everywhere was very quiet and I heard a very faint noise which could well have been the blower motor running very slowly. I couldn't hear a thing inside the car or feel any air movement. So I decide to disconnect the battery and check it out the following day. I've checked the drain current every day since and it's always been 30 mA!

I still think it's probably the blower - or rather - the regulator that's the cause of the problem. The blower gets 12 V direct from the battery but the 0 V line comes via the regulator. When the ignition is off, the regulator should supply 12 V to the blower so that there's no voltage difference across it. But I guess if one of the control transistors in the regulator leaks a bit, then the output transistor will pass some current and the blower will run very slowly. Most regulator failures either put 12 V on the blower so that it won't run at all, or 0 V on the blower so that it runs flat out even with the key out.

I suspect that I have an intermediate case which is also intermittent - but I can't prove it. So every evening I am checking the leakage current......

Anybody had anything similar?

Mike
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post #2 of 21 (permalink) Old 01-09-2011, 10:28 AM
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Did you try the AC test sequence to see if it reports or resets the regulator? or pull the codes (i will try and find the correct pin for you) Otherwise its a set of tails through the vent hole in the bottom of the battery well so you can always get access if you drain it flat...

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post #3 of 21 (permalink) Old 01-09-2011, 01:00 PM
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I have a same kind of problem, battery drains flat after 8 days without usage. It is very annoying that I always have to take care how long the car is stopped, and because it is not a daily driver, I had to get used to it that after 5 or 6 days i have to disconnect the battery always, cause if i don't, then te battery won't be able to start the car.

And sometimes I can hear the same kind of noise from the blower motor when the car is stopped.

And i have problems with the regulator + blower motor, during driving the car suddenly a 3-5 times clicking noise comes from behind the glove box and the blower motor stops, then no matter what i press it doesn't start again and then some minutes later it just starts by itself.
I have not tried the AC test sequence yet, but i will.

At this moment i'm also charging my 100 Ah battery too (it is 10 months old), and now i have a 74 Ah replacement battery in my car (from another car of mine, a Citroen Xm V6).
The drain current of my car is also between 30-40 mA. The car audio repair shop told me that compared to other cars this value is higher.

Anyway i plan to take the car some weeks later to my indy repairman to fix this and then i will know what caused it.
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post #4 of 21 (permalink) Old 01-09-2011, 03:57 PM Thread Starter
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Originally Posted by Merc600sec View Post
Did you try the AC test sequence to see if it reports or resets the regulator? or pull the codes (i will try and find the correct pin for you) Otherwise its a set of tails through the vent hole in the bottom of the battery well so you can always get access if you drain it flat...
TBMK the regulator is a totally analogue device, so I don't think it's resettable. But I have to say that, every morning when I press the boot button, I wonder whether it's going to open. So, if I don't manage to nail the problem down, the set of battery tails through the vent might become a sought after accessory.

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.........
And sometimes I can hear the same kind of noise from the blower motor when the car is stopped.

And i have problems with the regulator + blower motor, during driving the car suddenly a 3-5 times clicking noise comes from behind the glove box and the blower motor stops, then no matter what i press it doesn't start again and then some minutes later it just starts by itself.

The drain current of my car is also between 30-40 mA. The car audio repair shop told me that compared to other cars this value is higher.
Very interesting. If you hear a noise when the ignition is off, I suggest that you take the blower air intake off and see if the blower is running: this is what I intend to do if I can repeat my high drain problem. If it is running then I think the problem is that a semiconductor in the regulator is breaking down and a new regulator should fix it.

The problems you have with the blower switching off after a clicking noise suggests to me that you have a relay problem. I would have thought that this would be the auxiliary pump relay in the relay box behind the main fuse box (it also supplies 12V to the regulator control circuitry) - but I don't know whether this is anywhere near the glove box in a LH drive car.

As for a leakage current of 40 mA, say, after 8 days you would have used up only 7.7 Ah so it could cause absolutely no problems with a decent 100Ah battery. So you must also have an intermittent, drainage current in the hundreds of mA range.

Mike
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post #5 of 21 (permalink) Old 01-09-2011, 04:41 PM
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TBMK the regulator is a totally analogue device, so I don't think it's resettable. But I have to say that, every morning when I press the boot button, I wonder whether it's going to open. So, if I don't manage to nail the problem down, the set of battery tails through the vent might become a sought after accessory.



Very interesting. If you hear a noise when the ignition is off, I suggest that you take the blower air intake off and see if the blower is running: this is what I intend to do if I can repeat my high drain problem. If it is running then I think the problem is that a semiconductor in the regulator is breaking down and a new regulator should fix it.

The problems you have with the blower switching off after a clicking noise suggests to me that you have a relay problem. I would have thought that this would be the auxiliary pump relay in the relay box behind the main fuse box (it also supplies 12V to the regulator control circuitry) - but I don't know whether this is anywhere near the glove box in a LH drive car.

As for a leakage current of 40 mA, say, after 8 days you would have used up only 7.7 Ah so it could cause absolutely no problems with a decent 100Ah battery. So you must also have an intermittent, drainage current in the hundreds of mA range.

Mike
One thing to consider for those of us in the Winter months in the Northern Hemisphere:

I've noticed that, in the winter months, my S320 is in a "battle" to recharge the battery.

In colder temperatures, a battery holds less charge. I make short trips to run errands (grocery store, library, bank, etc.) Lots of "power-consumers" on, too. The headlights, fogs, climate control, seat heater(s), rear window defroster, etc, etc.

This is my third winter with my S320. To better maintain the charge of my battery, I put it on a charger for 24 hours (Saturday afternoon to Sunday afternoon, for example) every 2 weeks or so:

Make sure always that you NOT have your ignition "on" or the key in the ignition. Disconnect BOTH battery connections to charge.

I back my car into my garage, open the trunk/boot to charge.

This always returns my battery to full capacity, or as full as possible.

Make sure your trunk/boot light in not "on" when the lid is closed. I've heard that some battery-drain problems are caused by this.

Our W-140s "must" consume some nominal power, if just for the alarm and trunk and door lock receivers to monitor changing input.

Longer daylight, warmer temperatures, less power consumers in use and more frequent and LONGER car trips make maintenance charging of my battery unnecessary in the warmer spring and summer months.

Mercedes does mention to check the condition of our battery's charge frequently thoughout the year, too.

These cars drive a lot of electronics, comfort/convenience features, etc.

Topping Up My Battery,


James Combs,
Salt Lake City, Utah USA (expected low temperature tonight, 9 F!)
1997 S320, 88,300 miles (with a two year old Duralast battery from AutoZone)
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post #6 of 21 (permalink) Old 01-09-2011, 09:29 PM
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Check this WIS info. Looks like it isn't applicable to your car, but who knows...
Attached Files
File Type: pdf AC-REST.pdf (7.8 KB, 325 views)
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post #7 of 21 (permalink) Old 01-10-2011, 12:48 AM
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Couple of things here..My suggestion about the AC diags sequence would be to confirm all flaps and relays etc are in the correct positions and are not consuming. It is important to note that there is an automatic CAN BUS test sequence that runs after ignition is switched off. this records faults and tries to clear problems. It starts with the lower order faults and progresses up to major ones, if it can not clear a certain fault it will continue to try,this would include turning relays on and off in sequence this has been known to cause an action loop with no solution consuming power. The way to stop it would be to read record and action them, clear all the codes (possibly more than once)and repair any faults and then test again. Hope this helps you...

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post #8 of 21 (permalink) Old 01-10-2011, 02:29 AM Thread Starter
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Check this WIS info. Looks like it isn't applicable to your car, but who knows...
Thanks for the response, myarmar. I haven't seen that notification before but I did at first think that the REST must be my problem. However, the control for the REST is via the a/c controller and is supplied via fuse #18 (always hot). Since pulling fuse #18 made no difference when I did have the high drain current present, I concluded that the REST couldn't be the culprit.

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Originally Posted by Merc600sec View Post
Couple of things here..My suggestion about the AC diags sequence would be to confirm all flaps and relays etc are in the correct positions and are not consuming. It is important to note that there is an automatic CAN BUS test sequence that runs after ignition is switched off. this records faults and tries to clear problems. It starts with the lower order faults and progresses up to major ones, if it can not clear a certain fault it will continue to try,this would include turning relays on and off in sequence this has been known to cause an action loop with no solution consuming power. The way to stop it would be to read record and action them, clear all the codes (possibly more than once)and repair any faults and then test again. Hope this helps you...
That's very interesting, Merc600sec: I don't know anything about this and will investigate. Certainly, when I monitor the current drain, all sorts of values appear, as the PSE and soft-close pumps go through their cycles after I open the boot and switch of the boot lights. But there are also some drain currents which take longer to settle down before I get to my 30 mA standing current.

While I still think that a failing regulator is the most likely cause, it seems odd that so far it has only occurred at very low temps - semiconductor breakdown is usually a high temp problem. So will investigate. Thanks.

Mike
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post #9 of 21 (permalink) Old 01-10-2011, 02:47 AM Thread Starter
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Originally Posted by 97S320Jim View Post
One thing to consider for those of us in the Winter months in the Northern Hemisphere:

I've noticed that, in the winter months, my S320 is in a "battle" to recharge the battery.

In colder temperatures, a battery holds less charge. I make short trips to run errands (grocery store, library, bank, etc.) Lots of "power-consumers" on, too. The headlights, fogs, climate control, seat heater(s), rear window defroster, etc, etc.
.......
Topping Up My Battery,

James Combs,
Salt Lake City, Utah USA (expected low temperature tonight, 9 F!)
1997 S320, 88,300 miles (with a two year old Duralast battery from AutoZone)
Thanks, James. When I say we had cold weather in Wimbledon, I don't mean that cold (9 degF) - that it is really quite cold. It was more like 27 degF overnight minimum.

I've had my 140 for 11 years now and this is the first time that I've had this problem so I'm pretty sure it's not a simple decline of charge in cold weather, especially as it also happened with the new replacement battery.

Mike
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post #10 of 21 (permalink) Old 01-10-2011, 05:44 AM
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It does sound like a regulator issue.The key is definitely that the drain does not go away with any fuse pulled.It can only be a device with a constant unfused hotwire (or fusible link). I am curious to see if you can tell if the blower motor is running when the key is off. Keep us posted.
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