Green BMS - smart opensource battery management system

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green-bms
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Green BMS - smart opensource battery management system

Post by green-bms »

Hello, I would like to share my project with you, in the hope that it will be of interest to you.
I made a BMS that I installed in my daughter's e-max scooter (16s 48v)
It is a BMS for prismatic cells (I used Winston 60Ah), with modules that are fixed to the positive pole of each cell.
Each module is based on Attiny microcontroller and communicates in I2c with the control unit based on Arduino Mega.
The BMS is controlled and managed via an Android application on a smartphone connected to the BMS via Bluetooth.

I decided to share Open Source the whole project on this site:
https://www.green-bms.com/

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T1 Terry
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Re: Green BMS - smart opensource battery management system

Post by T1 Terry »

Had a quick look through some of the videos, nicely done, thanks. First question, what is the upper limit to the cell count? If I wanted to control 90 LTO cells, is this something that could be expended to perform this task?
Next, I see you use the loss balancing method, is it possible to develop this concept to active balancing so the over capacity is moved to the under charged cells rather than turned into heat?

Thanks for sharing

T1 Terry
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green-bms
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Re: Green BMS - smart opensource battery management system

Post by green-bms »

Hi Terry,
first of all consider that this project is a diy experiment done during my free time, that I decided to share (when I checked that works well) in order to allow others people to improve and derive it.
Actually the theoretical limit is 40 cells, It's a limit due to the small RAM of Arduino Mega on Control Unit. It could be increased upgrading the control Unit to another microcontroller card such as "Arduino Due", that have more RAM.
Furthermore, the practical limit that the system may have due to the I2c network must be taken into account. The only way to understand this limit is to physically connect the cells, but I need to make an investment in money that I can't make at the moment. For the moment I can certify that with 16 cells there are no problems.
About active balancing, actually I'm not able to do it (this is my technical limit!!! :roll: ), I suppose that can be very difficult active balancing in a system composed by several individual cell modules.
To manage the heat problem, I have provided a temperature sensor attached to the resistances, which blocks the balance when the temperature exceeds a user-defined threshold.
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brendon_m
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Re: Green BMS - smart opensource battery management system

Post by brendon_m »

T1 Terry wrote: Thu, 09 Sep 2021, 10:48 If I wanted to control 90 LTO cells, is this something that could be expended to perform this task?

T1 Terry
I looked into using LTOs for a project a while back and I have a vague recollection that you can run them without a BMS as the cells will handle under/over voltage fairly well.
Don't hold me to that but might be worth investigating
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4Springs
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Re: Green BMS - smart opensource battery management system

Post by 4Springs »

Well done!
Very smart.
sleeperpservice
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Re: Green BMS - smart opensource battery management system

Post by sleeperpservice »

Very nice and thanks for sharing
green-bms
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Re: Green BMS - smart opensource battery management system

Post by green-bms »

If you are interested, you can buy the PCBs that make up Green BMS, at the following links:
Cell module: https://www.pcbway.com/project/sharepro ... v_0_2.html
Interface board: https://www.pcbway.com/project/sharepro ... v_0_1.html

On each page you can download the Gerber file to purchase the PCB wherever you want and you can download the BOM (bill of material) file for PCB assembling.
By the BOM you can purchase directly from PCBway the PCB assembled, but I have no idea about the costs...
Bye!
T1 Terry
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Re: Green BMS - smart opensource battery management system

Post by T1 Terry »

green-bms wrote: Thu, 09 Sep 2021, 16:12 Hi Terry,
first of all consider that this project is a diy experiment done during my free time, that I decided to share (when I checked that works well) in order to allow others people to improve and derive it.
Actually the theoretical limit is 40 cells, It's a limit due to the small RAM of Arduino Mega on Control Unit. It could be increased upgrading the control Unit to another microcontroller card such as "Arduino Due", that have more RAM.
Furthermore, the practical limit that the system may have due to the I2c network must be taken into account. The only way to understand this limit is to physically connect the cells, but I need to make an investment in money that I can't make at the moment. For the moment I can certify that with 16 cells there are no problems.
About active balancing, actually I'm not able to do it (this is my technical limit!!! :roll: ), I suppose that can be very difficult active balancing in a system composed by several individual cell modules.
To manage the heat problem, I have provided a temperature sensor attached to the resistances, which blocks the balance when the temperature exceeds a user-defined threshold.
Thank you for the reply, for some reason I missed it, I'll put it down to old folks disease :lol:

I've ask the question on this product https://www.aliexpress.com/item/1005001 ... 5088%22%7D to see how the 24 cell units would be interconnected to balance from the first 24 cell group to the forth 24 cell group .... no doubt the answer will be in Chinglish and make very little sense if any, but we live in hope.

T1 Terry
Green but want to learn
T1 Terry
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Re: Green BMS - smart opensource battery management system

Post by T1 Terry »

brendon_m wrote: Thu, 09 Sep 2021, 21:31
T1 Terry wrote: Thu, 09 Sep 2021, 10:48 If I wanted to control 90 LTO cells, is this something that could be expended to perform this task?

T1 Terry
I looked into using LTOs for a project a while back and I have a vague recollection that you can run them without a BMS as the cells will handle under/over voltage fairly well.
Don't hold me to that but might be worth investigating
They won't just die if over voltage or under voltage occurs, but cycle life takes a hit. Getting a voltage read out of all 90 cells and an alarm trigger if a cell goes under or over voltage is the next hurdle, the 1.5v to 2.85v operating range doesn't match up very well with units made for the 2.5v to 4.2v range that covers LFP, lithium cobalt and LiPo voltages.

T1 Terry
Green but want to learn
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