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Few weeks back, when parking my SL-500 into my garage, suddenly, the red battery light came up in my dashboard and at the same time an unusual burned electronic smell penetrated my nostrils…! After searching for the root cause, found out that a capacitor in the BCM board had burned and made a large hole in the center of the BCM board. So, it was so damaged that it wasn’t a chance to refurbish it. So, went around the internet in search of a replacement and shortly thereafter found out that all around the planet sellers of used BCM wanted north of $1000 for the part which no telling how much life it had left. I wasn’t too thrilled about that and started the research for a fairly priced replacement option.
After reviewing all available documentation, I learned that the BCM is a combination of a DC to DC battery charger and a digital controller. Since the vehicle was able to operate without the “consumers”, the first step I took was to install a DC-DC charger to maintain the starter battery charged. Afterwards I needed to find a way to bring the consumers online. This was indeed a complex job since I needed to find a way to send digital messages to CAN B in order to re-activate the “consumers”. Basically, I needed a computer programmed in a way that could replicate these missing BCM messages. Fortunately, one of my LinkedIn connections is a savvy computer software developer who I teamed up with to adapt a programmed microprocessor to interface with the CAN-B bus to send the BCM missing messages. A few days later a “little brain” was up for testing.
After installing the “microprocessor board”, my “consumers” came back online, the battery red light disappeared…. I had a moment of eureka…….! I was thrilled to experience how a very small piece of electronics could do so much. At that time, the myth of an irreplaceable BCM went straight to history. There are still few simple knots to tie, but the main job is done.!
The picture below shows this tiny computer fitted inside my BCM box taking care of business…!
If any of you are curious about this tiny computer, see the datasheet attached and you will be amazed to see how much computing power is packed into this little board.
Most impressive and you've performed yeoman's work in resolving this issue.
Any chance you could provide some slightly more technical information on the interface and programming? I can understand the software would be proprietary but I'm curious as to the implementation. You and your LinkedIn friend may have a hobby that can earn you a few dollars. Perhaps sell a few to one of the aftermarket MB parts houses? Also curious if the code is "locked " into the memory to prevent someone from just reading it out or if this will become an open-source solution for the MB community.
Again, well done!
Bbirdwell, if you happen to own one of these programmed boards, with the proper hardware and skilled programming knowledge, you could see what the scripts are. It is like reading the Config file in a Computer. I think a regular individual even with an advanced study in electronics won't be able to program it. The hardware is cheap...the software is the key..! As I said, we are still tying some knots and soon all aspects will be addressed we may offer pre-programmed units for sale. The DC-DC charger is very common and there are very smart units out there. You could even plug a solar panel just in case you leave the car at the airport for a month!
HLG 600, to address your question, the only component of the system handling high current is the DC-DC charger, but it has fuses on both positive ends, so no risk if the unit fails. As far as the microprocessor the max current through it I don't think is more than 2 amps, so a 5 amp fuse will assure protection. It has a latent consumption of 20 MiliAmps..!
The bottom line is: the risk of fire is negligible, and the components are easily found in the market for many years to come. Sofware programmers are also plentiful...! Wise one's..cannot tell?
I am glad someone has taken the challenge and decoded the critical CAN BUS codes. That was always going to be the real challenge.
How far do you intend to take this? Just a basic "get the car working with minimal functions" solution, a fully functional BMS replacement, or something in between?
Look forward to future development of the module, especially as it potentially could save many cars in the future, and could take a little worry out of R230 ownership.
Thank you my friend....! This work is mainly attributed to my colleague the "software developer genius" who was able to get that little computer to do what the CAN B bus wanted to hear. So far, with the system previously described all the functions in the car are active excepting the radio, which I am trying to find where is the "link" to get it to speak. I am considering replacing that old system with a 7" touch screen unit anyway. The only thing you won't get with this system is the "charged condition" on the rear battery, which could be replaced by simply using a digital voltmeter with very low current draw permanently connected to the rear battery, so in that way you know that if your voltage is under 11.5 volts, you should wait to charge it before opening/closing the Vario roof.! Another potentially missing function is the detection of a malfunctioning alternator, which could be detected with the above-described voltmeter or a LED with a gate that allows power to the LED when voltage drops under 12.7 volts...! This is part of a development journey which for sure will end with all corners covered..!
As once upon a time a great philosopher said: The need is the mother of all inventions...!
Below is how my trunk looks. I temporarily have the liner off while I get all my connections completed and have access to the BCM box. The charger connector with the blue cable is for attaching a solar panel if necessary! That charger will trickle charge the starter battery once it is fully charged.
When finished, the only thing visible will be the DC-DC charger.
With the BCM out or a dead BCM did you lose connection to CAN BUS B? I am asking since I can not connect to any module on CAN BUS B and have a red light on my dash Battery, Visit workshop. I don't want to go tracing the CAN BUs wires if the reason is a dead BCM.
Are you planning on offering this as a plug and play package to the community? If so, any idea what you might sell them for? My BCM is currently working but I now its only a matter of time. Id really like to avoid the inevitable fire.
thx
Excellent!
If you're not already on this FB page, there are a few people who are working on ways to eliminate the BCM and keep both batteries without error messages. Initially, the group was to gather information in hopes of getting MB to help, but that proved to be a dead end... so people have taken it upon themselves to find a way to eliminate the fire hazard.
* Looks like links to FB are not allowed. You can search for: "Mercedes BNS/BCM Fires"
What a fantastic find @elMacko ! Your post made my day.If it’s not too much trouble, could you please ask your friend to publish a GitHub link for this? I would love to contribute to its development with my knowledge.
Most impressive and you've performed yeoman's work in resolving this issue.
Also curious if the code is "locked " into the memory to prevent someone from just reading it out or if this will become an open-source solution for the MB community.
@elMacko has the only board ever sold. Because selling these was not my intention when I undertook the effort. I wanted to put the time in now to solve a problem I may eventually face in my SL65, while my BCM is still working. (I'm going to upgrade the caps and mosfets in the BCM btw, so hopefully I'll never need this myself)
For those who don't want to hassle with sourcing the board, re-flashing it, etc. I do have a few boards already made up. I've considered making them available on eBay (for both buyer and seller protections).
The price is $99, pre-flashed, pre-wired and tested. You would still need to figure out the DC-DC converter and the wiring of the batteries. This device only keeps the rest of the car thinking the BCM is present and happy.
It does actually monitor battery voltage. One of the other CAN messages has battery voltage in its data. If this device sees that it's below 10.8v, it will set a code just like the original BCM.
The MCU is an STM32F105, not 107. Still very powerful. And this board has an unused CAN port. One could make a really cool product with simultaneous access to both CAN-B and CAN-C.
Like this for instance: https://github.com/rnd-ash/mb-w211-pc
This board is a repurposed "MB CAN Filter" <- Google this. It's made for nefarious purposes. But it fits the need here and it's inexpensive. (AliExpress)
If you have any questions about the device, feel free to ask.
Last edited by Michael Pitts; Jul 11, 2024 at 04:42 PM.
Reason: typos
HLG 600, to address your question, the only component of the system handling high current is the DC-DC charger, but it has fuses on both positive ends, so no risk if the unit fails. As far as the microprocessor the max current through it I don't think is more than 2 amps, so a 5 amp fuse will assure protection. It has a latent consumption of 20 MiliAmps..!
The bottom line is: the risk of fire is negligible, and the components are easily found in the market for many years to come. Sofware programmers are also plentiful...! Wise one's..cannot tell?
@elMacko has the only board ever sold. Because selling these was not my intention when I undertook the effort. I wanted to put the time in now to solve a problem I may eventually face in my SL65, while my BCM is still working. (I'm going to upgrade the caps and mosfets in the BCM btw, so hopefully I'll never need this myself)
For those who don't want to hassle with sourcing the board, re-flashing it, etc. I do have a few boards already made up. I've considered making them available on eBay (for both buyer and seller protections).
The price is $99, pre-flashed, pre-wired and tested. You would still need to figure out the DC-DC converter and the wiring of the batteries. This device only keeps the rest of the car thinking the BCM is present and happy.
It does actually monitor battery voltage. One of the other CAN messages has battery voltage in its data. If this device sees that it's below 10.8v, it will set a code just like the original BCM.
The MCU is an STM32F105, not 107. Still very powerful. And this board has an unused CAN port. One could make a really cool product with simultaneous access to both CAN-B and CAN-C.
Like this for instance: https://github.com/rnd-ash/mb-w211-pc
This board is a repurposed "MB CAN Filter" <- Google this. It's made for nefarious purposes. But it fits the need here and it's inexpensive. (AliExpress)
If you have any questions about the device, feel free to ask.
This is incredible work and a true breakthrough for the R230 community.
For those who don't want to hassle with sourcing the board, re-flashing it, etc. I do have a few boards already made up. I've considered making them available on eBay (for both buyer and seller protections).
The price is $99, pre-flashed, pre-wired and tested. You would still need to figure out the DC-DC converter and the wiring of the batteries. This device only keeps the rest of the car thinking the BCM is present and happy.
It does actually monitor battery voltage. One of the other CAN messages has battery voltage in its data. If this device sees that it's below 10.8v, it will set a code just like the original BCM.
If you do list these extra boards you have on eBay I would be highly interested in picking one up. Please let me know if you would like me to shoot you a DM to facilitate this, or if you do choose to list them on eBay please post the link here for everyone else who may be interested in also picking one up! Thanks!
If you do list these extra boards you have on eBay I would be highly interested in picking one up. Please let me know if you would like me to shoot you a DM to facilitate this, or if you do choose to list them on eBay please post the link here for everyone else who may be interested in also picking one up! Thanks!
I put up a listing yesterday evening for the last one I had pre-assembled and it sold right away. Sold listing: https://www.ebay.com/itm/145885052383
I have several more boards I need to assemble and test, then I'll make a new listing. Probably sometime this evening.
Guys, when my BCM burned and I realized the kind of technology inside the BCM board that wasn't simple to recover. I thought that I never ever could have been able to ride in a convertible anymore, unless I pay the used BCM price, which I saw as the last of the last choice in a desperate situation.
Thanks to this breakthrough provided by Michael, I am just thrilled to have my car back which the features I thought were lost. Now I don't worry about fires or being stranded in the road away from home due to a BCM or the ABC which has been solved using coil overs. So, I have significantly lowered the chance of failures.
The bottom line is that BCM burning is not how or when, it will be a 100% chance of occurring at any time in these cars. No matter if you use fuses since the minimum necessary for DC-DC will be around 50 amp, and with that current a capacitor may burn a hole in your board.
If I were in your shoes, I will get one of these " wonders" from Michael as an assurance to have on hand when your turn for a burned BCM comes..!
I put the remaining four boards I have in an eBay listing: https://www.ebay.com/itm/145888851062
I have more boards on the way. Should have them in a few days.
These are pre-assembled and tested. As a reminder, this only one part of the complete total solution. You will still need to find a way to keep the batteries charged and isolated. This device only tells the other modules in the car that the BCM is alive and well, to extinguish the red battery warning and bring electric consumers (roof, perhaps more) back online.
If you order one, please state which variation you would like. Either with or without a CAN connector. If you mount this in a gutted BCM case, you won't need a connector. If you want to install it near the rear SAM, a connector makes it much easier as you only would need to tap +12v and ground, and plug the connector in the the bus located next to the SAM.
The rear battery will continue to charge as normal, nothing will change with that circuit.
I think it should be possible to connect the front battery directly to the alternator, (via the 200A fuse), then via a 10A diode, then also fit a 10A diode to the positive of the rear battery.
This will mean both batteries will charge constantly, but won't connect to each other.
The alternator should be able to handle the load OK (as when both batteries are charging normally, it's doing all the work anyway).
OR fit a DC-DC charger for the front battery only, but these are pricey. Relay K57 should be removed for safety (but with the BCM removed it's lost its power anyway).
Tom, no need to get so complicated..! If you join 30a and 30 you will have a system of two batteries in parallel, and the alternator will be charging both at the same time..as you stated, but do not know what secondary consequences it may bring...!
I see clear the alternator will be fully working charging the two batteries. Another solution would be using a single battery, buy you would have to use a heavy gauge cable from the rear towards the front...and when the battery is drained, no starter!!!...
To simplify these issues I just connected a 25 a/h dc-to dc which will trickle charge the starter battery when fully charge, giving a break to the alternator..! When the vehicle is off, the two batteries are completely isolated.. This is a simple proven technology....! There are chargers with higher a/h, but more than 25 a/h is unnecessary since you could restore the charge loss for starting in less than 5 miles of driving! My system works like a charm and it is safe and reliable.!
Last edited by elMacko; Jul 14, 2024 at 11:07 PM.
Reason: Adding pic
What happens when the starter battery goes dead, does the rear battery load get transferred through the 30 amp fuses, or are they isolated? I can also see the lead acid and the agm rear battery needing different charging rates
I've had a Victron battery charger on my generator and it was very high quality. And the bluetooth capability made it that much better.
I think we could use something like this, combined to a microcontroller, to replicate ALL of the original BCM's capabilities. Including controlling the K75 and K57 relays. The MCU could control the DC-DC with it's switch, and possibly make use of the bluetooth capability to control and read voltages, etc.
Would this be worth the effort? I estimate it would take a couple months to get something up and running.
Last edited by Michael Pitts; Jul 15, 2024 at 12:03 PM.
Reason: typo,add another link
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
