What makes you think that is the issue?

 

Old capacitors are known problems in all electronics TV's, PC's and cars.
With r230's regularly going up flames, I want to avoid any headaches.

 

These are the parts that seem to be the culprit of the fire. I’m not privy as to what these do,but know they look like this when everything else is fine. The new BCM version does not have these in it, even though the part number is the same. I don’t know what these are, but they are the issue I believe.

 

How old are these batteries?

 

These are the full pictures from this bcm, fully functional, fully charging, no capacitor bulging or discharge on the board. Hopefully it is as simple as capacitor replacement, but with Mercedes redesigning the board , not so sure.

 

Here are the pictures of the older version, and the new version, both same part numbers, but as you can see, the affected burned area on the new version is different.

 

Interesting.
I don't know squat about electronics, but in the new version it looks like they eliminated those square blocks.

 

I do know that capacitor manufacturing technology from around 30 years ago, is different from today because back then, they used acid inside the capacitors and today they can make them without acid inside. Over a bunch of years they will eventually leak acid, and who knows what will happen once they do. I learned this because audiophiles with Klipsch speakers made in the 1980s, those speakers still sound incredibly good today but there are two companies that sell new Printed circuit boards that you can retrofit your speakers with, in order to have new capacitor technology.Up until I learned this, I was unaware that those speakers even had a circuit board in them, with capacitors on board! I have a pair of La Scala speakers made in 1987, and while they still sounded perfect after 36 years, and none of the capacitors showed any signs of leakage, I opted for new boards with new tech capacitors just because they were available. Also not very expensive. A brand new pair of La Scalas cost about $14,000!!
It will be interesting to learn whether new capacitors in your BCM resolve your problem! Have you gotten nomenclature on the new pieces indicating that they are indeed made differently than the originals? I got a new BCM a few months ago from Mercedes, cost around $600 if I recall. It likely has re-designed, newer technology capacitors in it? I certainly hope so.
Then there's the Clark Rupp guy who rebuilds the V12 coilpacks, and the electronic parts he uses are newer/updated technology parts than what the cars were originally made with, I'm not sure whether those are capacitors or diodes... But one of his rebuilt coilpacks is better than a brand new one for that reason.

 

Those square blocks are capacitors too:

 

The squares can be diodes, caps , resistors SMD's.

 

Back to my original question:

Does anyone know the dimensions of the nine 470uf capacitors?

 

I could be wrong, but I think you may be blazing a trail that's never been gone to before. You may have to take out your BCM and remove those capacitors and physically get them in hand to learn what you're asking. However, maybe it's possible that someone has done this before. Best of luck to you. Replacing some small parts like that is certainly a nice idea compared to spending hundreds of dollars buying a new BCM!

 

And depending on what part number BCM you have they may be different. Getting the board off of the aluminum housing may prove difficult as well. Good luck with your venture

 

Those components are almost certainly capacitors.

Positioned that way, they would act as ground paths for high frequency noise. Each one will have a low reactance (similar to resistance, but only applicable to AC voltages) at a different frequency.

Used a lot this way in high end test equipment.

What is interesting, is early versions of these SMD capacitors were made from Tantalum material, which is well known for absorbing moisture from the air.
They also do not like surge currents, such as powering on a circuit, and usually have a surge resistor in series to limit currents.
Both these failure modes result in them shorting out internally, and either going bang, or literally setting on fire and smoldering.

I restore old test equipment, and usually have to replace all these components for modern equivalents. They usually last Ok if the equipment is used regularly, as in service they will be kept warm, and so not absorb moisture from the air.

Modern versions are made from ceramic. They generally replace low value electrolytic capacitors as are cheaper and can be soldered more easily with automated processes.

Interesting the new version omits them!

 

Those big electrolytics are probably smoothing capacitors. If they are not leaking or bulging then they are almost certainly fine. You can measure them. Read up on the capacitor plague, but this was solved almost certainly by the time these modules were made.

So why do they catch fire? Since all the feeds to the BCM would presumably be fused except for the direct connections to the batteries (disregarding the huge fuses in the pre-fuse block), maybe it's a short to ground from one of the battery hots. If you look at the pictures of the fires, it's the peripheral wiring that's burned, not the BCM itself. So what would cause a short? One of the regulators shorting to ground maybe. I would replace all the regulators first as a more logical way to safeguard aagainst an unknown potential condition.

 

Most of the blown/burned BCM fires I've seen have blown/burned Blue 470uf capacitors, some have blown MOSFET's, and blown/burned SMD capacitors.

 

If anyone has a dead/blown/burnt Battery Control Module PM me.

 

I'm starting have battery problems with my 2003 SL500.
Yesterday my starting battery was dead even though I have a battery tender on it and started it up fine last week.
Used a jump box on it, started right up, both batteries charging at 14.0 v.
I want to order the capacitors in the BCM before I take it out and need to find of the size of the 9 470uf capacitors, 13mm x 27mm ???
I'm leaving both batteries charged up and disconnected until I replace the caps.
View attachment 2838336

Were you able to locate the capacitors that you're looking for? If not, try DigiKey. They are a supplier of several components. In addition to the capacitance, you'll also need the voltage rating (should be listed on the side). Also, it looks like these are aluminum electrolytic capacitors. Good luck.

 

Don't know if this would pertain to the SL's fire problem, but Lincoln Navigator's have a recall due to battery monitor causing fires. The fix was to add a fuse in line.
Lincoln Recalls 142,734 MKC SUVs Over Fire Risk (autoweek.com)
I wonder if that would do any good on the SL. Your BCM may still be cooked, but maybe your car wouldn't catch fire.

 

Were you able to locate the capacitors that you're looking for? If not, try DigiKey. They are a supplier of several components. In addition to the capacitance, you'll also need the voltage rating (should be listed on the side). Also, it looks like these are aluminum electrolytic capacitors. Good luck.

I usually order electronic parts from Digi-Key or Mouser.

Don't know if this would pertain to the SL's fire problem, but Lincoln Navigator's have a recall due to battery monitor causing fires. The fix was to add a fuse in line.
Lincoln Recalls 142,734 MKC SUVs Over Fire Risk (autoweek.com)
I wonder if that would do any good on the SL. Your BCM may still be cooked, but maybe your car wouldn't catch fire.

I was looking at adding at least a 200 amp fuse (or resetable circuit breaker) between the battery and the BCM, there is a 200 amp fuse inside, it won't prevent a dead short in the BCM, but should prevent a fire.
The cable for the charging the front battery has a 100 amp fuse (under the 200 in the passenger footwell).

 

Mercedes is too cheap to provide a fix, they would rather act ignorant and let a few cars burn.

I have some fuses/holders on order to isolate the BCM. I want to test before I share, but I am going to start with 30A. The only power that the BCM needs to draw from the rear battery is for the DC-DC converter to charge the front battery. Max. charging current is 15A, so I think 30A will be adequate. The 100A fuse in the front battery connection is mainly to limit draw from the front battery when K57 is activated. The car is capable of drawing much more, but power to many modules is limited by CAN messages when in emergency power mode. K75 also disables the cigar lighter and trunk 12V accessory outlet.

 

Mercedes is too cheap to provide a fix, they would rather act ignorant and let a few cars burn.

I have some fuses/holders on order to isolate the BCM. I want to test before I share, but I am going to start with 30A. The only power that the BCM needs to draw from the rear battery is for the DC-DC converter to charge the front battery. Max. charging current is 15A, so I think 30A will be adequate. The 100A fuse in the front battery connection is mainly to limit draw from the front battery when K57 is activated. The car is capable of drawing much more, but power to many modules is limited by CAN messages when in emergency power mode. K75 also disables the cigar lighter and trunk 12V accessory outlet.

Yeah, charging the start battery doesn't need that high of amps.
Also disconnecting the k57 emergency start relay eliminates another potential problem, but the car won't get a extra boost if the starting battery is weak, not a problem if you keep your batteries in good condition.

Mercedes will never admit to a problem UNTIL enough people die when their house burns down.
They still are acting ignorant to the infamous eco-junk biodegradable engine wiring harnesses.

 

"MikeJ65 said:
Mercedes is too cheap to provide a fix, they would rather act ignorant and let a few cars burn.
I have some fuses/holders on order to isolate the BCM. I want to test before I share, but I am going to start with 30A..."

Mike,

Please keep us informed as to your progress in developing some fail-safe fusing for the SL battery control module fire-starting issue. It would be a great public service if you come up with a solution and post to this forum. While the problem is rare, I have installed a trunk-mounted battery cut-off switch in my 2004 SL600 to eliminate this BCM fire risk. A large portion of my house is directly above the garage in which my SL600 is stored and I am very concerned about the potential for my resting car to start a house fire.

I think you are on the right path to a "fix", as it is very doubtful that Mercedes will ever admit to a problem with the unfused BCM design and aging electronic components being culprits for some of the R230 trunk fires that have happened over the years.

 

I ordered 2 30 amp MIDI fuses off ebay, the smallest available.

 

I am also adding 2 voltmeters or 1 voltmeter and a switch or a push button (to starter battery) to monitor both batteries.

 

I do have a Android stereo, but I think I'll put a voltmeter in or in front of the clock on top of the dash.
I just looked, I have a flat spot I can mount it between the headlight switch and steering column and see it through the steering wheel.
Starts blinking under 11.5v
Voltmeter 12v

 

I added the 2x 30 amp Midi fuses, ran the car for 15 minutes, works fine.
I did not drive.
You should use fuse holders - the fuses can't support the cables, I temporarily zip tied the cables to a black piece of plastic I found in the old parts bin, and covered them.
I did not connect the k57 relay, I taped it off .
You will need to have it on the unfused side or better, add a 75-100 amp? fuses to BOTH wires, eliminating another potential for a fire.
This is not a problem if both batteries are in good condition and fully charged.
Couldn't install the voltmeter, it did not show up Fri/Sat USPS doesn't deliver until Tues.

 

Test fit the voltmeter in the clock on top of the dash.
I needed to file to open up the top and bottom, need to add filler pieces on the sides.
The plastic is so brittle it broke 3 times, so I will be getting another.
Will be adding a switch to toggle between front and rear batteries on my filler panel on the side of my android stereo.

 

I will pull my BCM soon to check for any signs of overheating or burning. A timely preventative check for any owner. Those burnt components in functioning BCMs are a real worry.

Looking at the two 30A fuses you've put in, is one on terminal 30a and one on 30? I haven't had a good look at the module yet. A 30A fuse can allow at least 360 Watts each fuse; that's a hell of a lot of heat. I wonder if the fuse rating could be halved safely.

I still suspect that the internal shorts in the BCM come from dodgy regulators.

Removing relay K57 is a great idea. With it in place and activated, due to a low front battery, the new 30A (or maybe 15A fuse) would certainly blow.

The only negative is the car may not start if the front battery gets weak. Solution: monitor it, or carry a portable jump pack.

The fuse and relay-removal option vs a potential fire - well that's an obvious choice.