Electric - is it draining - PeachParts Mercedes-Benz Forum

tivoliman · #1 06-02-2007, 10:14 AM

The 300E sits in the parking lot all week.

Seems when I get there on Friday, the battery is dead. The battery is new and the alternator has been replaced. As a matter of fact the battery was recharged by the time I got home.

So I'm thinking there's a "small electric leak (drain)" occurring.

Suggestions for chasing down the "short" is appreciated.

Your suggested work around is also appreciated. (I've considered removing the battery)

thanks again

pistonhead · #2 06-02-2007, 12:48 PM

The surest way of checking for battery drain is to connect a hand held multimeter, set to an amps reading. The multi meter must be connected IN SERIES between the negative terminal of the battery the removed earth strap from the battery to the body.

In English, disconnect the negative strap on the battery, set the multi meter to read amps, connect the black lead of the amps meter to the battery post and the red lead of the amp meter to the disconnected strap.

If you get a negative amps reading swop the leads connecting to the battery and disconnected lead.

With all doors shut, ignition off and the bonnet push button switch, if fitted, held down. Take a reading on the amp meter. This should have a reading of approximately 0.5amps - 0.7 amps.

Keep taking your reading for about one minute. The first 30 seconds or so may have a much higher reading due to the fact the internal light would take about 30 sec. - 40 sec. to go out, when this happens the reading should drop. Any higher reading over about 0.7 amps indicates you have some thing consuming battery current. This additional consumption has to be located and rectified.

The sort of consumables could be the boot light remaing on, even though the boot lid may be shut. To eleminate this from the equation, remove the bulb to the boot compartment and read you amp meter again, if there is no change to a high reading then you need to search else where.

Repeat the same exercise to eliminate the glove box bulb, the door switches individually, but in this case disconnecting the door switch. Carrying on, check readings with the alarm armed or disarmed, switch off the radio. Identify the fuses and disconnect each fuse to the electric windows to see for any difference, check the clock fuse by disconnection and checking on current draw. Consider the alternator in your tests, by disconnecting the battery feed lead to the alternator, infact even the block connector to it also. That is the general idea.

Remember to reset the amp meter after use, current can only be measured with the multi meter connected in series to the electrical circuit. It is measuring volts that the meter is connected in parallel. Take head as the meter can be damaged if not properly connected!

haasman · #3 06-02-2007, 12:51 PM

Your car, in its stock configuration should easily wait over a week without significant battery loss.

If it were mine I would look at voltage drains from an after market alarm and a stereo with external amps. Often these amps are hooked up and left on continuously.

To check your drain, use a volt-ohm meter at the battery. When the key if off you should have just a tiny current flow for say, your radio head station setting memory.

Haasman

tivoliman · #4 06-02-2007, 06:10 PM

My old meter looked dead, so I bought a new Analog MultiMeter

With range set to 0-50mA

The car is showing 30 mA is that (30/1000) .03 Amps.

If it is .03 amps - that doesn't sound like much.

Removing the fuse for the clock reduced the reading to 20 mA.

No other fuse reduced it more, though I found it interesting that removing sme seemed to raise the mA to 50.

There is a "stray green" wire hand tied to a fuse. Tried to trace it but it get;\'s buried. There is a radio amplifier

haasman · #5 06-02-2007, 07:43 PM

The "stray green wire" bothers me ..... wonder what that is doing.

It occurs to me to ask .... why did you buy a new battery? For curing the same problem? It sounds like you may not have a battery problem but a charging problem. When the engine is running, what is the read out across the negative and positve termminals on your battery with your new meter?

BTW, NEVER run the engine with the battery disconnected. It would fry your alternator.

Haasman

tivoliman · #6 06-02-2007, 09:40 PM

I purchased the car from a used car only dealer.

When I test drove the car, the battery was dead, they jumped it to start for the test drive. They agreed to provide a new battery "for the deal". Hence I have a new battery.

The Green wire is disconnected, and there appears to be nothing different. The wire "may have been" for the cell phone that was installed, with a prior owner. I found and removed the microphone.

There is an amplifier attached to the radio. The amp usage seemed to increase when I disconnected the amp, and the car is not running.

If I read the meter right - the voltage reading is 15, with meter across the battery terminals.

Thanks

haasman · #7 06-02-2007, 10:05 PM

I am not a pro on this but "15" indicates over charging.

The problem could be something as simple as a bad voltage regulator which is located on the back of the alternator. Actually easy to change and not too expensive. See this link for a '90 300E.

I would disconnect the amp first. See whether it is drawing power. If not, take your car to some place and have the charging system checked. If you car needs just a voltage regulator, easy to do.

Haasman

Stoney · #8 06-02-2007, 10:15 PM

Doesn't the remote monitor for the keyless controller eat up some amperage while in the "wait" mode?

Same approach, no one has suggested the alternator, either its not getting enough run time ti fully charge the battery or isn;t charging correctly when it is run or the battery itself has a defective cell.

What you need to do is run a set of jumpers off the alt to your meter and measure output and run a set to the battery and see if what is coming out of the alt is getting to the battery.

Example: I had a Volvo that had a system that the trigger voltage for the charging system was passed thru the dash idiot light and when the bukb died so did the charging circuit. Possibility here?

I also had a client that found the existing telephone amp in the trunk was wired to power antenna circuit for power (belore the relay) and merely disconnecting the handset controller wiring from the fuse box did not totally kill the system or its electric draw. Ditto?

Sounds like you need a session with a good MB tech or a good 12V Tech.

tivoliman · #9 06-03-2007, 11:44 AM

The problem is solved - thanks.

Seems the "green wire" was the culprit - removed it yesterday, and today all is well. Plenty of electricity today.

This thread does provide a great summary of how to look for leaks, by putting the multimeter in serial between the battery and the cable. I also tried removing the fuses and putting the meter in serial with the red probe down (bottom of fuse area) and the black probe on the top -

This also discusses how to see how many volts are charging - by setting the meter to volts and probing the two battery terminals.

Great information

Others contributed - thanks - but a special thanks to haasman, who even asked inquisitive questions, and Stoney's simple comment - it's probably an aftermarket device.

I am soooo happy the car IS NOT going to the shop for them to perform an electric system review - that can take hours.

But I am going to the AutoZone for a free charger system check.

tivoliman · #10 12-02-2007, 03:41 PM

The electric short was caused by

the Overload Relay

Located behind the battery (behind the black plastic shield)

Mercedes Part Number - 201 540 32 45

At Fastlane:

http://catalog.worldpac.com/mercedesshop/sophio/quote.jsp?header=header.jsp&footer=&product=2015403245&partner=mercedesshop&baseurl=http://catalog.peachparts.com/&clientid=catalog.mercedesshop&cookieid=28P0XHN6N28P0XHZWJ

I tried using a used one - no luck - but with a new - all paoer (electric) issues went away.

Learned from a friend that had the same issue.