My distributed Battery Management System project

[nlc]

Yes good idea ! I have a drill percution which do a lot of spark, I will try !

Today I finished a board to test the ability to drive a TFT screen in RGB mode (with no integrated driver) with direct connection to the external bus of a microcontroller, and using and external SRAM on the bus as framebuffer.
It's work very well, I use DMA to refresh the TFT data with the framebuffer content, and I am able to have a 20Hz refresh rate, more than needed for this kind of application.
I also tested a complete framebuffer update (blue/red color), which consist to change the value of all 130.560 words (16 bits) in the framebuffer, because it's a 480x472 4.3" TFT screen. It works well, it takes 50ms to fill the entire framebuffer ! A small video, I switch blue/red every second :

http://www.youtube.com/watch?v=Ny4uQXYD0wA&NR=1

[nlc]

Today I tested your EMI immunity experiment with a big drill, with the master (my computer) requesting slaves datas every 200ms (5 Hz refresh rate) to have a lot of communication data in the wires. But with the led flash of 50ms every valid received frame, on the video the flash seems to be completely erratic !! In fact it's not the case, and there were no error, you maybe will see "erreur BMS = 0" on the laptop screen, but you need good eyes !!!

http://www.youtube.com/watch?v=UmJaK8qrxyQ

On other side, I think about the display, need the opinion of every interested people. I think something like that can be great ?



- The ampmeter with real time battery pack current (when touched, switch to WATTs)
- A generic zone for display various message, date and hour, etc...
- The voltmeter with real time pack voltage. When touched, switch to a new page to monitor all cell voltage and temperature (with an histogram for exemple)
- The vehicle speed and total mileage
- The "fuel" gauge, based on amp hour which enter/leave the battery pack, and pack capacity configured. When touched, display another interesting informations : total amp hour provided by the pack, total number of charge cycle, etc..
- 2 independent trips informations : distance, duration, average speed, amp hour used, average W/Km or W/Mi. When touch on the zone, display secondary information of the trip (percentage of regen, etc...)

[nlc]

My work on this BMS project continue, the slave board are totally finished (hardware+software), now just need real dynamic testing on a pack.

I currently work on the master board, because I think I will not sell any slave board without a master board to use them. This master board will be very evolutionary with a lot of possible functionalities.

Here is the general diagram of the board :



The schematic design is almost completely done, in some days I will reach the routing step

I found a great enclosure for this master board :

[nlc]

Some month are passed, and some news : I simplified the master board, to begin with something simple, here is the pcb, I sent it in production yersteday :

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Functionalities are :

- 12V supply
- Ignition input (to startup the master in discharge mode)
- Isolated charger mains detection input (to startup the master in charge mode)
- One relay contact output to indicate that charge is authorized
- One relay contact output to indicate that discharge is authorized
- 2 status Led output
- 2 free open collector outputs
- Serial port for configuration/firmware upgrade/bluetooth module option connection (for supervision and data-logging with a smartphone)
- BMS interface to first and last BMS slave board (2 to 255 slaves possible)
- 2 digitals/analogic inputs
- 2 analogic outputs (0-5V), to drive gauge for example
- Can bus
- SD card connector (to save datalog file for example)

[nlc]

The board will sit in this housing :

20121019_201849.jpg

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[agniusm]

This is great news. Cant wait for more on how your system performs. I dont know if it is relevant but perhaps it is possible to include individual cell SOC graph. bar? That would be good to see how cells behave under load to monitor for bad cells?
Any info on pricing for the main unit?

[nlc]

First the first software version I will only provide datalogging of cell voltage VS discharging current. It's already a godd way to see how performs cells under load. But in future release we can imagine a lot of integrated functionnality and beautiful thing on the touchscreen of an Android device !!

For the price of the master, I will know that soon, but I do everything I can do to have the lowest price as possible for a professional electronic grade. But I will not have big production quantity, so I think it will be around 120$, maybe a little less.

[nlc]

I just finished to solder the master board prototype :





This afternoon I begin functionals tests, but I am not worried

[Teh Stork]

Using N-chan mosfets with large dies could replace the relays. I use a simple charge pump circuit to bring their gate to 15V. You can also parallell smaller mosfets as much as you want, in this non-critical application avalanching and such isn't a problem.

My BMS basically has the same functionality as yours, just with lesser part count and rough samplings going all the time, and precise samplings requested once there is no power being asked for.

[nlc]

Relay are used if there is a need to control high voltage which must be isolated from local +12V ground area
Other output are open collector transistor, referenced on the +12V area

[hydro-one]

WoW! You do nice work! This is a great system you have here!

[nlc]

Thank
Normally it will be commercially available soon...

[Farfle]

That's beautiful work man.

[circuit]

It amazes me how close you are to what this guy did three years ago:
http://hr-ev.blogspot.com/2009/06/bms-c ... works.html
The topology is the same, even communication protocol and all other stuff. Even part count seems very similar. It's almost like a copy-paste solution in slightly different shape.

[ctirad]

There is a bunch of another BMSes which look almost the same. It's one of the most common design.
I personaly like this particular one. Nice and clean routing of the PCBs, SMD components, etc.. However, It's still yet another BMS with dedicated MCU on each cell with master board. I'd rather see a modular design with one board for a group of the cells, say 4 to 8. There is no such BMS available in neither commercial nor DIY market, AFAIK.