Re the BMS PCB Random thoughts in no particular order..
1) I was thinking put your PCB/s at the end of the pack where the fan would be.
A thin? PCB the width of the pack, or three small interconnected pcb's that fit into the openings, one per block. Connectors facing inwards accepting those plugs.
Maybe use the fan mount bolts holes or studs on the end of the packs to secure it/them, whatever.....
The OEM fan could mount over it as normal and provide airflow for the bleed resistors when balancing.
(I'll do a YT vid with some thoughts.)
2) If you want to
replace the BCM you have to do a
lot of stuff to keep the MCM happy.
a) Measure/count current in out and have a running or faked SOC that is stored between drives.
b) Have a serial data stream on BATTSCI containing current, voltage, temperature, Soc, flags etc.
c) Accept serial data from the MCM on the METSCI bus..
d) Other stuff I have probably forgotten.
3) Yes it would be possible to add a BCM Interceptor to your physical PCB.
The current version of the BCM Interceptor PCB fits inside the MCM and has two simple 5V logic level high/low inputs to control (enable/disable assist/regen).
I think we should keep the OEM BCM and let it do it's thing. That also avoids a lot of hardware development and harness chopping modifying. We get to put the 4x OEM temperature sensors in the new packs and use the OEM current sensor, SOC counting etc all as normal.
Fake the ptc strips with a 30R resistor as we do now for most setups.
Feed the BCM taps with a simple BCM Fooler resistor matrix.
That's well proven and reliable and is easily configurable for higher voltages than OEM with a pre-resistor. (This could be on your pcb)
Use a BCM interceptor (fitted inside the MCM or on your pcb) to interface between your BMS and the car. Again that's well proven and reliable.
Your BMS cpu just has to output a 5V logic high/low on two discrete lines to enable disable assist/regen.
The cell voltages could be output via CAN or more likely serial data on the HLine and be picked up by an OBDIIC&C like the LTO etc.
Most people doing mods like this will have an OBDIIC&C plugged into the car, might as well use it
You could have your CPU listen on the serial HLine and when it gets a send me the cell voltages request packet from the OBDIC&C/Android app/etc etc it just spits them out onto the HLIne/Bluetooth for the OBDIIC&C/Phone to display.
That would be fairly simple to implement.
So if we kept the OEM BCM then we would need....
1) Your simple BMS pcb with two 5V logic level outputs to enable/disable assist/regen via the onboard BCM interceptor.
A 5V HLine serial 9600 baud I/O port to exchange cell voltage data or commands with the OBDIIC&C on request.
2) A BCM tap fooler resistor matrix. (You could put that on your pcb and use your HV connections etc)
The builder/converter would simply cut off the tap harness from their orange end board and solder it your pcb.
3) A simple BCM Interceptor inside the lightly modified MCM or on your PCB.
4) An optional OBDIIC&C to display stuff from your BMS and/or send/receive commands like adjust voltage/balance setpoints etc.
5) Your BMS would do all the balancing stuff autonomously and just toggle the logic level protection request outputs when things (cell voltages) get out of hand!