4-channel BMS with daisychain bus

[sonachan1]

Hi all,

I'm looking into getting a batch of boards made. If you're interested, can you let me know by Friday 7th June so I can get a rough idea of numbers. I'll get a quote based on the number we need, then you'll have the opportunity to commit to buying them or not based on the quote.

PM me if you're interested.

[johu]

I didn't get around to posting the firmware properly on github, so here are the binaries for now.

Fuses on the cell board must be
- efuse 0xFE
- hfuse 0xD7
- lfuse 0xE2

[Teknomadix]

removed

[johu]

Very cool. Will start a wiki page for the BMS so you know how to use it. https://openinverter.org/wiki/4-cell_BMS
Thanks for the upcoming support, I'm very grateful that I don't have to organize shipping and such.

[Teknomadix]

removed

[nailgg]

Also. Would like to suggest officially naming this the "Heubner BMS"

Johannes is probably too kind to do this, but I feel compelled to correct this before you have hundreds of them manufactured: It's "Huebner" not "Heubner"

[Teknomadix]

removed

[johu]

Nail, thanks for pointing it out

I have updated the documentation: https://openinverter.org/wiki/4-cell_BMS

If anyone feels inclined to design the CAN version then here is your starting point: https://github.com/jsphuebner/bms-hardware (Isolator-2.0.*)

[dima]

Hey Johannes have you looked at "fastboot" as UART bootloader for ATTiny? I did an unrelated project with attiny and it was working great even with Attiny13! Very small written in assembly (510 bytes) here is a copy https://github.com/dimecho/ATtiny13-Pla ... r/fastboot

[johu]

Hi Dima, on the cell modules there is no UART but the custom protocol. The boot loader works quite well and takes up 500 bytes (written in C)

[sonachan1]

I've created this wiring diagram for Johannes' BMS and added it to the Wiki as well.

This diagram has been edited. The connections on the 1st isolator module connector JP2 were reversed. Also swapped the position of JP2 and JP3 on the diagram to match the actual PCB

[johu]

Beauty
On other news my top secret China contact will be sending me 100 populated boards in about 3 weeks.
Some are reserved for Damien and Andy and a few other chaps who dropped out of my head (hope will remember later)

[JaniK]

Beauty
On other news my top secret China contact will be sending me 100 populated boards in about 3 weeks.
Some are reserved for Damien and Andy and a few other chaps who dropped out of my head (hope will remember later)

I did not find it in shop, how much you ask for the boards?

[johu]

They are not up yet but maybe I should do so for pre-orders?
I think 10-15€ should be a realistic price range

[johu]

Meanwhile I have lost track of who was interested in 4-cell boards. Could everyone please speak up here.

On other news I will design a CAN isolator board based on a Blue Pill that is otherwise through-hole. I expect quantities to be rather low to begin with, so through hole makes more sense also as it won't be many components. The isolator will also have a differential input for a current sensor, a relay, an open collector PWM output and an open collector analog output for faking fuel tank pots.

Concerning the CAN protocol I'd like to reuse an existing one, so what is your favorite BMS CAN protocol, compatible with SimpBMS?

Next step would be collecting preorders in the shop and when X boards are ordered I'd order a larger batch of like 1000 or so.

[Oskar]

"Just a friendly reminder.."

Sign me up for 24 4-cell boards and two CAN isolator boards. If there are any left that is

[D@F]

hello, i'm interrested to make a bms for a 100s battery pack, what do i need to buy ?
could it be compatible with sk innovation 4.4vmax cells ?

[tom91]

Concerning the CAN protocol I'd like to reuse an existing one, so what is your favorite BMS CAN protocol, compatible with SimpBMS?

Since it is 4 cells per board, copying the Mitsubishi outlander responses (see attached info) would be good, so you would be pretending to be an 12 cell slave board.

Balancing in the Mitsubishi Outlander scheme uses a target voltage, I do not know what you have in mind.

If the current sensor info can be shared pretending to be a CAB300/500 that would be easy to reuse too.

Code: Select all

     ID 0x3c2:
  for (int i = 0; i < 4; i++)
  {
    inbox = (inbox << 8) | inMsg.buf[i];
  }
  CANmilliamps = inbox;
  if (CANmilliamps > 0x80000000)
  {
    CANmilliamps -= 0x80000000;
  }
  else
  {
    CANmilliamps = (0x80000000 - CANmilliamps) * -1;
  }

so a simple 32bit signed value in mili-amps

[johu]

hello, i'm interrested to make a bms for a 100s battery pack, what do i need to buy ?
could it be compatible with sk innovation 4.4vmax cells ?

So for 100S you'd need 25 cell boards and one or more isolators depending on how the cells are distributed in you car. If they are all in one place one isolator is enough. For 4.4V cells the resistor network would be a bit different, will ask the manufacturer if they mind doing different ones on some boards.

@tom Outlander protocol looks reasonably straight forward.

I have the layout of the CAN isolator done, will order some boards maybe next week.

[tom91]

@tom Outlander protocol looks reasonably straight forward.

You can see how easily I can add more 'slave postions' if needed. There is no really 'excess' data in the can structure, so if you feel like you need more let me know.

https://github.com/tomdebree/OutlanderP ... anager.cpp

Code: Select all

void BMSModuleManager::decodecan(CAN_message_t &msg)
{
  int Id, CMU = 0;
  
    Id = msg.id & 0x00F;
    CMU = (((msg.id & 0xFF0) - 0x600) >> 4);
    
  modules[CMU].setExists(true);
  modules[CMU].setReset(true);
  modules[CMU].decodecan(Id, msg);
}

The code above and the rest of the structures used currently limit it to 63x12s slaves (756 cells monitored), I would expect the canbus to be the bottle neck before saturating reserved memory.

For me the basics are covered to get the cell info you want to make the higher level decisions on.

[johu]

Yes 756 sounds like a gentle limit (3kV)
Ah yes I also use a target voltage for balancing, the same value for all cells.

[D@F]

hello, i'm interrested to make a bms for a 100s battery pack, what do i need to buy ?
could it be compatible with sk innovation 4.4vmax cells ?

So for 100S you'd need 25 cell boards and one or more isolators depending on how the cells are distributed in you car. If they are all in one place one isolator is enough. For 4.4V cells the resistor network would be a bit different, will ask the manufacturer if they mind doing different ones on some boards.

@tom Outlander protocol looks reasonably straight forward.

I have the layout of the CAN isolator done, will order some boards maybe next week.

ok if it's possible i'm with you for 25 cell board and two isolators .

[johu]

I got the first 3 prototype boards from China today. Tested one and it's good.
I found that I needed another gain correction in hires mode. Basically 4 correction factors for the resistor dividers and one for the internal 20x gain stage. Now the measurement is almost on par with my 34401A meter

[langoo]

I got the first 3 prototype boards from China today. Tested one and it's good.
I found that I needed another gain correction in hires mode. Basically 4 correction factors for the resistor dividers and one for the internal 20x gain stage. Now the measurement is almost on par with my 34401A meter

Great stuff! I might be interested in some boards for a project of mine. Did you put up an schematic/PCB design and software on GitHub?

[johu]

Yes, hardware is here: https://github.com/jsphuebner/bms-hardware