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Michael, as far as I understand,
1.-The BCM monitors the charge level of the rear battery and if it is under a voltage threshold, turn off the consumers while the alternator charges the battery, and turns them on once the battery is charged.
2.-The BCM monitors the charge level on the starter battery and establish a connection through K57 to charge the starter battery. and opens it when it is fully charge.
Now I quite do not understand the function of the DC-DC built in the BCM board since the charging is supposedly to be done through K-57..unless it is just a trickle charger!
The function of the DC-DC standalone charger, it determines voltage differential between the input and output to charge the second battery, then goes in trickle mode when it is fully charged. When the ignition is off completely disconnects the starter battery doing as the K57 relay..!
Your wonder "micro controller" fools the BCM and creates the CAN messages to enable the consumers, but cannot indicate when the rear battery is low or defective, which could be easily determine using a voltmeter in the dashboard! So, the trick to completely emulate the BCM would be a "device" that measures the rear battery voltage and turns the power off to the "wonder microcontroller" and perhaps send a message to the dashboard saying, "CONSUMERS OFF." ! Seems pretty achievable for a guy like you!
BTW, I am enjoying being able to roll that hardtop into my trunk and let the stars shine over my head..! No radio yet but sooner or later I get an android to replace it!
Right. I wouldn't use this same circuit as the emulator. I would need one with a couple ADCs to sense voltages and some MOSFETs to control the relays and perhaps the DC-DC converter (if it's externally controllable). I think the bulk of the work would be gathering all of the "acceptance criteria" then writing the software to meet it.
Luckily we have the PDF which describes the various BCM functional modes (normal, emergency, etc)
This new controller could even use the signal from the EIS (N72) to wake up, just like the OEM BCM.
And if it could simply plug-in to the BCM harness for ease-of-install, even better.
After a bit of investigation, I'm envisioning a module to sit beside and interface with this DC-DC converter. The module would monitor both voltages and do all the things the BCM does with relays and throwing codes.
The DC-DC would be wired much like this, but reversed in that the Aux battery receives the alternator charge and the starter battery is connected to the output of the DC-DC.
It's really cool that you can use your smart phone to also monitor and adjust the charge settings. This would have so much more functionality than the BCM, would be more reliable and less expensive.
I think this could easily cost less than $500 for everything. Whereas used and unknown condition BCMs are going for $1000 - $3000 on eBay the last time I checked.
I have six more BCM emulators ready. Search for "Mercedes Benz R230 BNS/BCM CAN Emulator - Fix Dash Warning" on eBay.
These are the same kind elMacko has installed in his BCM case. (Small green with an LED)
07-15-2024, 12:01 PM
