Interfacing: model 3 PCS <--> aem EV BMS-18 master

[jokeitch]

Starting a thread to ask some questions, I'll be updating this as things become clearer and hopefully have a full guide one day

First question:
The M3 PCS needs to see the CP and pp pins on the j1772 port, as well as of course see L1, L2, and PE (gnd)

However the bms-18 master also needs to see the status of CP and PP

Will both systems having access to those pins cause some trouble? Will they interfere with each other?

Second question;
Does the PCS need to do a lot a canbus chatter with whatever BMS is present? If so, will I need to look into tweaking the PCs controller firmware to output messages on addresses the AEM VCU200 is expecting? I'm thinking along the lines of the VCU200 seeing the bms-18 is reading all modules as high and done charging, and needing to tell the OBC (the PCs in this case) to quit it.

third question
there's a power switch going from 12v to the PCS control board on the wiring diagram, what actually throws that power switch? would it be some kind of wake signal coming from the vcu200? don't the cp and pp pins control when to "wake up" and start charging when the car's off? Or is that power switch more like an optional cold shutdown switch you can toss in

[Mojave]

The AEM BMS only needs to see the CP and PP pins if the VCU is directly controlling the OBC. If not they can be left disconnected.

[jokeitch]

i got a response back from an AEM tech in relation to a different question about balance charging, and his response seems relevant to this

To start off, the VCU will only command the BMS-18 to balance cells while charging and when conditions defined by VCU BMS logic and user calibration parameters are met to do so. Also, the VCU CAN3/4 network should form a loop that starts at CAN3 and ends at CAN4 with all CAN3/4 devices being not terminated since the Can 3 and 4 ports at the VCU are internally terminated.

You can configure the VCU to only look for 1 BMS cell group (master) and configure the VCU to allow balancing of a single group however, doing this will take a very long time to balance the entire pack since you’ll be doing up to 18 cells at a time and only up to 3 cells per cell group will balance at once. If you had 6 BMS-18 units wired up, the system will balance 3 cells per BMS-18 unit at a time, cutting down the time required since you are now balancing a total of 18 cells at a time if using 6 BMS-18 units.



2- Again, balancing is commanded by the VCU only while J1772 charging. This requires that the BMS is wired to the J1772 port Prox and Pilot lines. This requires that a VCU compatible CAN controlled OBC is wired to the VCU CAN3/4 network, HV, and J1772 port along with charging related VCU calibration parameters are properly configured for the specific OBC in use and pack configuration.

When balancing conditions are met, the VCU will command the OBC to stop outputting current, command balancing of highest 3 cells per cell group, and then command the charger back on. It’ll then repeat this process until charging is complete. If options “ChargeTopBalance” is enabled, the system will continue to do this indefinitely until the VCU is powered down, otherwise the VCU and system will power down once “fully charged” criteria are met.

it sounds like the vcu will need to be able to see PE and PP at all times in order to balance correctly, as well as command the model 3 obc to start and stop charging

[jokeitch]

getting back into this, can damien's controller deal with being "told" to start charging without seeing the CP and PP pins?

it looks like the aem bms really wants to be entirely in charge of charging, and basically just bark orders at the OBC to start and stop on a dime

the signaling would be over CAN but idk if the Damien controller is ok with that (hopefully it is since i already got the hardware)