Mystery battery drain, 1980 300D. - PeachParts Mercedes-Benz Forum

rasper · #1 09-05-2015, 10:37 AM

The car will act fine for weeks. Then overnight the battery gets drained. There are no lights left on; the trunk light is off, and no noises are coming from the car.
It has a two year old Bosch battery that tests out good.

Four nights ago we had a steady rain all night and it discharged overnight. I charged it up and the next night it drained again.
Two days ago I disconnected the ground terminal and put an ammeter between the neg. post and the cable, I got a fluctuating drain of from 1.5 to 7 ma. I have tested this a number of times over the past two days and there is no major drain.
I left the cable disconnected and the battery has stayed fully charged.

Sometimes when we have a torrential rain (I'm in the tropics) and I go out and start the car, the alternator light will remain on for a few minutes even though the engine and the alternator are bone dry.

One theory is that the battery has an internal problem that is intermittent, depending on bumps in the road. Other than that, I am stumped.

Richard

barry12345 · #2 09-07-2015, 05:40 PM

Possible glow plug relay stays on intermittently. Battery disconnects are cheap. Some things are initially so hard to find alternatives are a temporary solution.

In your case I would run a bulb from the glow circuit temporarily inside the car to monitor that circuit. They can be intermittent so the bulb should stay off. I would not trust the normal glow circuit indicator bulb as the indicator. The relay can malfunction I suspect and not light the normal indicator bulb.

Actually this is not that much of an unusual problem on these cars. Lots of cases have occurred over time.

rasper · #3 09-07-2015, 07:09 PM

I ran another test. I charged the battery fully and then disconnected the negative terminal. Over three days the battery discharged itself enough that, after the three days, when I reconnected the negative terminal the car did start initially, but not strongly, and after I shut it off and restarted it three more times, the battery was dead. I am assuming I have a bad battery.

Richard

interzonearts · #4 09-07-2015, 07:25 PM

Quote:

Originally Posted by rasper

I ran another test. I charged the battery fully and then disconnected the negative terminal. Over three days the battery discharged itself enough that, after the three days, when I reconnected the negative terminal the car did start initially, but not strongly, and after I shut it off and restarted it three more times, the battery was dead. I am assuming I have a bad battery.

Richard

It looks like the battery's dying but it doesn't mean you don't have a problem that accelerated it, like a hot wire grounding ever so lightly...somewhere. Or maybe not but if replacing the battery doesn't fix things you could use a multimeter, set it up to measure current right at the battery post.If you see some reading.. ( current flowing -when it shouldnt be!) Then go methodically pulling fuses, moving switches etc until you find the thing that causes the current meter to drop to zero.

rjz5400 · #5 09-07-2015, 08:30 PM

Hey interzonearts?
I am wondering How exactly do you set up the multimeter to show whether current is passing through the car?

I was going to start a new thread with this exact problem but I am not sure which settings to use?
The Omega Symbol?
the solid line and dashed line?
Not the speaker one for sure right? (the Continuity setting)

Thanks

and to the OP
I understand how frustrating it can be, I just swapped out a 2 year old AGM and my replacement also discharged over a day or so (not the new AGM) and I haven't put it in a brand new battery because I fear it will be damaged by a constant "Ghost" DRain......

rasper · #6 09-07-2015, 09:33 PM

I wrote in the original post

Quote:

Two days ago I disconnected the ground terminal and put an ammeter between the neg. post and the cable, I got a fluctuating drain of from 1.5 to 7 ma. I have tested this a number of times over the past two days and there is no major drain.

Richard

interzonearts · #7 09-07-2015, 09:51 PM

Quote:

Originally Posted by rasper

I wrote in the original post

Richard

I'm sorry, my reading skills ain't what they used to be. Anyways,it could be worn insulation on a wire that touches the ground sometime and sometimes doesn't.

interzonearts · #8 09-07-2015, 10:00 PM

Quote:

Originally Posted by rjz5400

Hey interzonearts?
I am wondering How exactly do you set up the multimeter to show whether current is passing through the car?

I was going to start a new thread with this exact problem but I am not sure which settings to use?
The Omega Symbol?
the solid line and dashed line?
Not the speaker one for sure right? (the Continuity setting)

.

You set it for A which stands for ampere (amp) which is a unit of current.

rjz5400 · #9 09-07-2015, 10:01 PM

Oh IC so the meter is the only thing connecting the battery to the car and any current flow goes through it. Posted at the same time, thanks inter I'll look for that when I test.

The clock should try a couple of Milla amps but that would take a year to run the battery down correct?

Keep us posted if you find the vampire thanks for thetips about finding mine. I'll update if I figure anything out. I hope the new battery solves the discharge problem for both of us!

Mxfrank · #10 09-07-2015, 10:26 PM

Since it's intermittent, a good approach would be to remove the fuses and let it sit for a bit. If it's a piece of fused equipment, then the battery won't drain.

rasper · #11 09-08-2015, 09:09 AM

Hey RJZ,

Quote:

Oh IC so the meter is the only thing connecting the battery to the car and any current flow goes through it.

You are correct. All of the current being drawn passes through the meter. So you don't want to turn on your key switch and have the glow plugs draw current through the meter.

Richard

leathermang · #12 09-08-2015, 09:18 AM

Take out fuses.... let sit and confirm no leakage..... reinstall ONE fuse at a time and check for leakage.

barry12345 · #13 09-08-2015, 09:25 AM

Once again before anything else test for the glow plugs intermittently remaining on. The drain they present when is so great they can cause a problem like you describe.

This is after a proper check of the battery with a load tester after a proper total recharge. Many small chargers take a very long time to bring a battery back up.

Any voltage read across the battery terminals after a proper charge that reads less than 12.6-12.75 volts. Either the battery is not properly charged yet or the battery is defective. A load test of the battery then indicates if the battery cells are able to deliver adequate current to meet the needs. This testing is available for free in many automotive parts stores.

Yes you can of course still have a bad battery. Far too many times people have not really checked the battery out properly and replaced it. Only to find out it was not the problem. Testing for the glow plug circuit intermittently coming on if the battery checks good is almost mandatory. Or would be in any 123d I own if the battery checks out.

Constant periodic draining of many batteries today drastically reduces their lifespan. This is also one heavy drain you do not want to find with the average amp meter portion of a multi meter. The maximum current they can deal with is only usually 10 amps. That is without an external shunt. Either an internal fuse in the meter would blow in my opinion or the meter could be damaged.

So just pull the battery and let an auto parts place check it out first. I was also wondering if it where really bad if there might even still be some warranty remaining.

The wiring system is in general pretty robust in these older Mercedes models as we do not seem to have as many electrical type problems as the average thirty year old cars would have in general.

Owning and learning how to use a multi meter is one of the better investments of time and little money. They can last a lifetime and are usable for many things other than cars. Saving you a fortune over the long haul.

The one thing that to me is pretty certain. Heavily draining a car battery very low many times can for all practical purposes kill them early in their life all too often as well.

We are all lucky that Germany did not copy the English lucas electrical systems. They have really earnt their title of being the prince of darkness years ago.

Maxbumpo · #14 09-08-2015, 09:44 AM

Richard,

In addition to a pre-glow relay fault causing the current drain, other common causes are the radio automatic antenna (if your car has one) or an interior light door-switch fault. I've even heard of the light in the glove box faulting on and causing similar ills.

I like the idea of the extra light on the glow-plugs so you have a nice visual indication that the glow plugs are energized when they should not be. I have an old turn-signal bulb socket with bulb that I use for a test light, attach a couple of wires to the contacts on the base and alligator clips on a few feet of wire, use some electrical tape to prevent a short and put the bulb out the hood at the base of the windshield. If you see it light while the car is not running, or light up after you've started the engine, then you know the relay is the source of your drain.

leathermang · #15 09-08-2015, 10:55 AM

Quote:

Originally Posted by barry12345

....... We are all lucky that Germany did not copy the English lucas electrical systems. They have really earnt their title of being the prince of darkness years ago.

I have at different times owned a 1957 Jaguar XK140 and Three MGC's...MGB's with the six cylinder engines...