[prensel]

Leaf BMS CANbus msgs (changed subject)

Hi all,

I've just started working on my first Leaf pack.
When reading out the BMS (using an Arduino with CANbus) it seems the Leaf BMS is not reporting the correct voltage for two cells.

Heres the CANbus dump for the 29 lines with voltages:

0 ID: 7BB DLC: 8 Data: 10 C6 61 02 0F AF 0F A8
1 ID: 7BB DLC: 8 Data: 21 0F A9 0F A9 0F A3 0F
2 ID: 7BB DLC: 8 Data: 22 9F 0F A3 0F 9F 0F 9E
3 ID: 7BB DLC: 8 Data: 23 0F A3 0F A3 0F A3 0F
4 ID: 7BB DLC: 8 Data: 24 A6 0F A7 0F A3 0F A4
5 ID: 7BB DLC: 8 Data: 25 0F A8 0F A4 0F A3 0F
6 ID: 7BB DLC: 8 Data: 26 A8 0F A3 0F A3 0F A3
7 ID: 7BB DLC: 8 Data: 27 0F A9 0F AC 0F A9 0F
8 ID: 7BB DLC: 8 Data: 28 A4 0F A9 0F 9F 0F 9A
9 ID: 7BB DLC: 8 Data: 29 0F A3 0F 9F 0F 9F 0F
10 ID: 7BB DLC: 8 Data: 2A A3 0F A3 0F 9F 0F A1
11 ID: 7BB DLC: 8 Data: 2B 0F A6 0F A1 0F A6 0F
12 ID: 7BB DLC: 8 Data: 2C A4 0F 9F 0F A3 0F A4
13 ID: 7BB DLC: 8 Data: 2D 0F A8 0F A7 0F A7 0F
14 ID: 7BB DLC: 8 Data: 2E A8 0F A6 0F 9F 0F A3
15 ID: 7BB DLC: 8 Data: 2F 0F 9F 0F 9F 0F 9F 0F
16 ID: 7BB DLC: 8 Data: 20 A3 0F 9F 0F A7 0F A7
17 ID: 7BB DLC: 8 Data: 21 0F A7 0F A9 0F A3 0F
18 ID: 7BB DLC: 8 Data: 22 9B 0F 9F 0F 9C 0F 9F
19 ID: 7BB DLC: 8 Data: 23 0F 9F 0F 9E 0F 9A 0F
20 ID: 7BB DLC: 8 Data: 24 A3 0F A7 0F A6 0F 9F
21 ID: 7BB DLC: 8 Data: 25 00 01 0E C9 0F ED 0F
22 ID: 7BB DLC: 8 Data: 26 96 0F A7 0F A3 0F A6
23 ID: 7BB DLC: 8 Data: 27 0F A4 0F 9F 0F 9F 0F
24 ID: 7BB DLC: 8 Data: 28 A3 0F 9F 0F A7 0F 9F
25 ID: 7BB DLC: 8 Data: 29 0F A3 0F A4 0F A6 0F
26 ID: 7BB DLC: 8 Data: 2A A6 0F A6 0F A3 0F A3
27 ID: 7BB DLC: 8 Data: 2B 0F A7 0F A3 0F A3 FF
28 ID: 7BB DLC: 8 Data: 2C FF FF FF FF FF FF FF

As you can see on line 21 the voltages are not correct: One cell is reported as '00 01' (0V) whereas the next cell is reported as '0E C9' . Measuring the packs gives 96V for both smaller packs and 192V for the big one. Without taking the covers off, I have not located the 'faulty' cells but i assume there are non and its just a fail of the BMS.

Anyone seen this before ?

Paul

 

[prensel]

Okay, problem solved
I had not connected the busbar between the smaller packs for safety.
Assumed each pack had its own daisy-chain of BMS wires, which is not the case.

 

[Solarsail]

What do you mean by smaller and larger packs? The Leaf is configured 48s2s2p I believe (48 modules of 4 cells each). All modules are of same size and so are all cells in the modules?

 

[prensel]

There is one big pack (at the rear) of 24 modules and 2 smaller packs of 12 modules each left and right
The 24 module pack is connected in series to the other 2 packs by means of a central safety plug. The BMS still works when the central plug is removed, so its actually monitoring two seperate packs of 24 modules each. But when the connection between the two smaller packs is removed the BMS stops working.

 

[Solarsail]

Ahhh - so you mean (24s+12s+12s)2s2p pack and 2x24s module BMS - actually 2x48s cells BMS. Thanks.

Is the charging 48s modules or 2x24s modules? And how do they balance the two 24s module packs to be equal?

 

[prensel]

Originally it is charging the modules in 48s because its wired like that. The central safety plug-kinda-thing (who has it btw or pictures of it) is just there to split the pack and voltage in half when it comes detached from the car (i think thats the purpose of it). But the BMS is apparantly also split in that it still monitors each half-pack. I also noted the BMS monitors if the central plug and main connector are attached because there are sense wires for that. It will set some bits in some CAN msg for that i assume.
But like I said. this is my first pack under 'investigation' and i'm trying to get all the CANmsgs pieces puzzled together. I can imagine more people have done this before but to find all the information in one place or from one source is hard. And there seems to be a difference between versions.

 

[Solarsail]

OK. I am just wondering if the charger is 346V and is charging 48s modules, while a BMS is monitoring and balancing the first 24s modules and another BMS the second 24s modules, what balances and makes sure the top half is equal to the bottom half?

 

[prensel]

Here's a good source of information about how the BMS is designed:

http://www.mynissanleaf.com/viewtopic.php?t=17470

I'm currently gathering all the CANbus information i can find from several sources and create a list of just those affecting the BMS. On the Leaf forums theres a lot talk about all other CANbus msgs but my main interest is just for the BMS on its own.