E300/W210: Battery drain - help! - Page 2 - PeachParts Mercedes-Benz Forum

scott19_68 · #16 02-25-2008, 11:56 AM

(bump - 'cause I'm commuting with the wife!)

Quick question: does the alternator get its link to ground through the engine? I have not checked the grounding cable(s) from the engine to the chassis yet - a friend of mine at work recommended using some long jumper cables directly from the battery to the alternator just to rule out any potential corrosion issues.

pimpernell · #17 02-25-2008, 02:25 PM

I would be very cautious about using battery cables directly connected to the alternator. If a lead were to slip off, or short out against the alternator casing you can fry the alternator diodes very quickly.

scott19_68 · #18 02-25-2008, 02:48 PM

Quote:

Originally Posted by pimpernell

I would be very cautious about using battery cables directly connected to the alternator. If a lead were to slip off, or short out against the alternator casing you can fry the alternator diodes very quickly.

Good point - I'll just attach the negative side only since that is the current path that I fear has excessive resistance.

scott19_68 · #19 02-25-2008, 10:41 PM

No luck with the jumpering the ground. I did notice that with the battery connected and the engine off that the voltage between the B+ connector on the alternator and ground is not the same as the battery voltage. It starts out at the battery voltage (~12.5V) but it decays fairly rapidly (around 5 seconds) to about 10.6 volts. As far as I can tell from the wiring diagrams is that the positive terminal from the battery is connected directly to the starter and the alternator - any idea what might be happening? If someone else with a E300D can check the voltage (car not running) between ground and the B+ terminal on the alternator and report back that would help me out tremendously...

michakaveli · #20 02-26-2008, 10:00 AM

scott, where are you getting your voltage reading? From the CCU or voltage meter from a location such as the cigarette lighter?

The voltage readings on the CCU are slightly lower than actual as there are resisters to slightly reduce the voltage going to the unit....

scott19_68 · #21 02-26-2008, 10:46 AM

I'm measuring the voltage with a multi-meter directly at the B+ terminal on the back of the alternator (see attached - green circle). The battery voltage at X12/3 on the fender is fine and I put the wire brush to all the terminals just to make sure. I pulled up the carpet on the driver-side to access X4/31 and check the voltages there but it is covered with some sticky felt material for protection - I think it is probably OK since the whole area is very clean and dry. I wire brushed the terminals at the starter (M1 in the diagram) as well as the connection back to X4/31 from underneath the car just to be sure they're OK as well.

Do you know physically where the connection between the starter and the alternator resides (blue square in diagram)? It is not referenced to a connector block so I am assuming that it might be splice within the wiring harness...

scott19_68 · #22 02-27-2008, 10:25 AM

I'm thinking about putting some ring terminals on a 6-8ft length of 8AWG copper wire and running from the alternator directly to the X12/3 terminal and see how that works. I cannot seem to find where the splice/connection between the lead to the starter and the alternator so I think this might be the a good test. I'm not sure of the wire gauge from X4/31 to X12/3 so this will only be temporary for debugging purposes. I'll post my results...

scott19_68 · #23 03-02-2008, 12:17 PM

Update: Traced alternator output terminal (B+) back to battery - the previously posted electrical diagram is wrong as it does pass through the X12/3 connector. Detached both ends and measured resistance of about 10 M-ohms so it's pretty much toast. During the process, found windshield drainage duct (#53 in attached) totally plugged with debris - it must have been water tight as it was completely composted black! So, water was pooling around these cables every time it rained for quite some time now.

I just soldered some ring terminals on an 8-ft length of 8AWG stranded cable - we'll see how that works in it's place.

raMBow · #24 03-02-2008, 04:08 PM

Quote:

Originally Posted by scott19_68

During the process, found windshield drainage duct (#53 in attached) totally plugged with debris - it must have been water tight as it was completely composted black! So, water was pooling around these cables every time it rained for quite some time now.

Well you made me go check mine. Appeared perfectly clean. Good to know. Keep us updated if that clears things up.

scott19_68 · #25 03-02-2008, 04:18 PM

Success! Battery is charging properly now with new custom cable from alternator to X12/3 terminal. I'll install a more permanently routed cable with proper friction tape later.

I guess this is a lesson for W210 owners - clean out those drainage ducts right after the fall season!

tallat · #26 04-08-2015, 06:21 AM

Quote:

Originally Posted by scott19_68

Thanks for the advice - here's a small update:

- Detached battery terminals and put on a trickle charger all night - this morning, charger was showing about 1-2A @ 13.8V.
- Pulled K40 and checked connectors and PCB - found an odd 'solder bridge' made up of what appeared to be tiny metal flakes (see attached). Cleaned up PCB on K40 and reinstalled.
- Put multi-meter in amps mode and put in series from positive terminal to car positive terminal - was showing about 0.75A. Connected battery to car terminals and checked battery voltage - now showing about 13.4V.
- Car started right up and seems to run great. CCU in diagnostic mode on sensor #24 showed 11.0 - turned on headlights and showed 10.8 - set blower to max and showed 10.7 - increasing engine RPMs did not make reported voltage fluctuate - turned both off and went back to 11.0 - battery voltage checked with multi-meter was 11.5V while idling (I assume the multi-meter is more accurate than diagnostic reported by CCU)
- Turned off ignition and checked battery voltage - showed 12.6V

Not sure what might be happening but I'm going to pickup a new battery later today.

Dear Scott,
Currently I am repairing my k40, I shall be really grateful if you could please attach a complete view (clear picture/s) of your k40's back circuit board. Right now I can see only middle section of your k40.

Thanks!

tjts1 · #27 04-08-2015, 09:50 AM

Scott last posted on this forum a year ago while selling his car. You might have better luck sending a PM or trying to find an email address.