Simp BMS

[kn1g]

I have the Tesla B-Class BMB (7s) with a SIMP BMS and I tried to test them the first time. I checked one BMB connected to three Nissan Leaf Gen 2 Packs (each pack is 2S 2P).

Temp test worked. Voltage somehow worked except for the last two reads. It splits my one BMB into two and shows wrong values for the "second" module.

I am an absolute beginner. I read as much as I can (manual, Forum, etc.) but obviously missed the puzzle piece what I messed up here.
I might have missed something obvious. The BMS shows the following:

Code: Select all

0
BMS Status : 1 Ready   |Balancing Active  6
Out:0000 Cont:0000 In:0000 Charge Current Limit : 16 A DisCharge Current Limit : 0 A


Modules: 2 Cells: 6 Strings: 1  Voltage: 22.220V   Avg Cell Voltage: 3.652V  Low Cell Voltage: 3.091V   High Cell Voltage: 4.012V Delta Voltage: 921mV   Avg Temp: 27.747C 

Module #1   15.01V   Cell0: 3.74V   Cell1: 3.74V   Cell2: 3.77V   Cell3: 3.77V   Cell4: 0.00V   Cell5: 0.00V  Neg Term Temp: 21.92C  Pos Term Temp: 33.52C
Module #2   7.21V   Cell6: 4.01V   Cell7: 3.09V   Cell8: 0.00V   Cell9: 0.10V  Cell10: 0.00V  Cell11: 0.00V  Neg Term Temp: 21.86C  Pos Term Temp: 33.68C
CANbus   0.00mA  9% SOC 6000.00mAh

The BMS config is set to:

Code: Select all

0 – slaves in parallel = 1
a – cells in series = 6

Why does it split the modules with incorrect reads? (I attached an image how I the pins are connected)

[tom91]

It splits it because of the way the BMB works it contains 2x bms slave ICs that can measure 6 cells each.

Split 4 - 3. You only wired up 6 cells to a 7 Cell BMB so the second part is upset.

[kn1g]

Ok thanks! I used 6 Packs (making it 14 cells) and attached two BMBs. Everything seems to work fine. I have 14 "modules" with 4 - 3 voltage readings that are all correct.
However, this means that I cannot run the BMBs if the number of cells/packs I want to monitor is not x%7=0? The BMB will always be "upset" and I cannot trick it such that I might have some voltage sens unused (e.g. as in my small rc-plane battery charger)?

What's the best way to debug why one temp sensor shows -83 degrees? I checked the sensors resistance and they seem to be fine. I swapped them and they work on the other pins.

Code: Select all

0
BMS Status : 1 Ready     14
Out:0000 Cont:0000 In:0000 Charge Current Limit : 0 A DisCharge Current Limit : 30 A


Modules: 4 Cells: 14 Strings: 1  Voltage: 52.734V   Avg Cell Voltage: 3.766V  Low Cell Voltage: 3.738V   High Cell Voltage: 3.792V Delta Voltage: 54mV   Avg Temp: 13.553C 

Module #1   15.01V   Cell0: 3.74V   Cell1: 3.74V   Cell2: 3.76V   Cell3: 3.76V   Cell4: 0.00V   Cell5: 0.00V  Neg Term Temp: 23.23C  Pos Term Temp: 34.33C
Module #2   11.29V   Cell6: 3.76V   Cell7: 3.76V   Cell8: 3.77V   Cell9: 0.00V  Cell10: 0.00V  Cell11: 0.00V  Neg Term Temp: 23.49C  Pos Term Temp: 34.29C
Module #3   15.10V  Cell12: 3.79V  Cell13: 3.76V  Cell14: 3.77V  Cell15: 3.77V  Cell16: 0.00V  Cell17: 0.00V  Neg Term Temp: -83.08C  Pos Term Temp: 15.67C
Module #4   11.34V  Cell18: 3.77V  Cell19: 3.78V  Cell20: 3.78V  Cell21: 0.00V  Cell22: 0.00V  Cell23: 0.00V  Neg Term Temp: 25.04C  Pos Term Temp: 35.45C
CANbus   0.00mA  61% SOC 36600.00mAh

[tom91]

However, this means that I cannot run the BMBs if the number of cells/packs I want to monitor is not x%7=0?

What's the best way to debug why one temp sensor shows -83 degrees? I checked the sensors resistance and they seem to be fine. I swapped them and they work on the other pins.

Tie the highest cells togehtor and check, so for 6 do 6+7 to cell 6.

What's the best way to debug why one temp sensor shows -83 degrees? I checked the sensors resistance and they seem to be fine. I swapped them and they work on the other pins.

If you swap BMBs does the issue move with the BMB or stay with the connector? It sounds like a connection issue or BMB solder joint issue (quiet common)

[kn1g]

If you swap BMBs does the issue move with the BMB or stay with the connector? It sounds like a connection issue or BMB solder joint issue (quiet common)

It seems to be the BMB. I switched them and it switches the incorrect temp reading. Ok, something related to the BMB like solder joint issue would have been the last I'd have expected thx!

[alexbeatle]

To confirm on the simpbms with Tesla SDU OI board.
If SDU params are Idc max=150A(consume) and Idc min = -500A(Regen), that means the simpbms discharge should be set to 150A and the charge to 500A limits, else bms will debate the drive performance?
Thanks in advance.

[tom91]

else bms will debate the drive performance

this depends on how you wired it up and configured any CAN to the SDU.

[alexbeatle]

this depends on how you wired it up and configured any CAN to the SDU.

No CAN to SDU from BMS. SDU controls the HV contactors and pre charge. BMS only allows SDU ignition to turn on if batteries are ok (but doesn't turn it off) and enabled/disable drive mode and charge mode.

I thought SimpBMS charge and discharge limits will control the Tesla modules satellite boards to debate on the module.

[tom91]

thought SimpBMS charge and discharge limits will control the Tesla modules satellite boards to debate on the module.

?!? what are you on about explain yourself please. There seems to be a big mis interpretation of how a BMS works.

[alexbeatle]

?!? what are you on about explain yourself please. There seems to be a big mis interpretation of how a BMS works.

Good thing I asked.
Do you mean that the satellite boards on the battery modules only collect data, but don't actually control the battery module - ex. don't allow current above xA?

[tom91]

No BMS has a method for limiting current. It can only cut off the current using the contactors.

A BMS monitors and gathers data then decides on limits and share this with the vehicle. (Balancing is the only thing it can do on its own of it does not have contactors)

[alexbeatle]

No BMS has a method for limiting current. It can only cut off the current using the contactors.

A BMS monitors and gathers data then decides on limits and share this with the vehicle. (Balancing is the only thing it can do on its own of it does not have contactors)

I see now. Thanks for your patience! That is a fundamental that I was missing.