Low cost / High performance universal BMS

[skeeterb]

Looking pretty good so far, sounds interesting. Hope you can make good progress on the master board.

[nlc]

For the master board, I continue to think about it, to be sure it will be usable by all DIY EV converter. In fact, for now I hesitate into 2 different concepts :

- The mother board is a BMS and nothing else, with ability to set on/off the charge, alert user, measure pack current, print info on pack SoC, manage the main power contactor (and the precharge) on ignition key request, do datalogging on SD card, and with communication port to get logs and configure the system on true rs232, rs232 over usb and rs232 over bluetooh.

- The mother board is a true complete "calculator" to manage all the EV : measure vehicle speed, propose some digital/analogic input to connect temperature sensors, current sensors, security switch and so on, manage main contactor/precharge, interface the BMS slaves directly to have direct access to voltage/temperature of all cells, having communication port for data-logging (CAN, rs232, usb etc...), and having a beautiful large color TFT screen to replace the original dashboard of the vehicle, with speed information, energy information, SoC, etc... In other words, a complete open platform specifically designed for EV, as a cycle analyst do for bike/scooter !

[skeeterb]

Wow! You have some pretty ambitious ideas. I want to start converting my own EV, but haven't got the money yet. You have a bunch of VERY good ideas with ease of use being important. will you be writing any code for accessing the BMS with a computer since you want to use a BlueTooth, RS232, or USB to access it?

[nlc]

Originally Posted by skeeterb

will you be writing any code for accessing the BMS with a computer since you want to use a BlueTooth, RS232, or USB to access it?

I am a very bad PC/user interface programmer, and I hate that I am an hardware and embedded software developper, it's why I want to open code and protocol to permit a very generic platform usable on any EV, with a lot a technical possibility and possible evolution.

At the beginning, for the bluetooth my idea was to dowload the datalog from the BMS directly with a smartphone, instead plug/unplud SD card, because the mother board is generaly under the hood, not easy to often plug/unplug the SD :/

And also, the smartphone can become the display of the dashboard, no need for the display option for those which have a smartphone.

[skeeterb]

Originally Posted by nlc

<snip>At the beginning, for the bluetooth my idea was to download the datalog from the BMS directly with a smartphone, instead plug/unplud SD card, because the mother board is generaly under the hood, not easy to often plug/unplug the SD :/

And also, the smartphone can become the display of the dashboard, no need for the display option for those which have a smartphone.

I like the idea of using a smartphone as your display for your BMS. All you would have to do is develop the app that would act as the interface and have it read the BT input then calculate and display the information. I've played with a little code for the PIC uC, and i've got a few programs I've developed that has a LCD that would display the information from the ADC and from other inputs. Only one of my programs has given me any trouble and that's the calculation of temperature from a temp sensor using the ADC. I've got some of my ideas on a forum called Electro-Tech Online. sorry if I hijacked your thread.

[nlc]

Originally Posted by skeeterb

I like the idea of using a smartphone as your display for your BMS. All you would have to do is develop the app that would act as the interface and have it read the BT input then calculate and display the information.

I see the thing in an other way, the display intelligence in the mother board and the screen just receive print and graphic commands. The advantage is to have minimum intelligence in the screen, thus it works only as a terminal. Thus the smartphone application is really simple, it just receive and execute print command, and send X/Y of the display touch action. By the way, there is alway just one firmware to release. I work I is for a customer and for the same product it can propose different screen options, or use a PC application to act as interface.

Originally Posted by skeeterb

I've played with a little code for the PIC uC, and i've got a few programs I've developed that has a LCD that would display the information from the ADC and from other inputs. Only one of my programs has given me any trouble and that's the calculation of temperature from a temp sensor using the ADC. I've got some of my ideas on a forum called Electro-Tech Online. sorry if I hijacked your thread.

No problem !! But difficult to answer without having the complete explanation about the problem

[skeeterb]

I would PM you but as my post count is still a little low, I'm gonna wait with that PM. It's just a calculation error i'm still trying to work out basically with the LM34 Fahrenheit Temp Sensor.

[mrbigh]

A very realistic idea would be to go modular for add on specific and complex features.
The function of pre-charge and main contactor handling is better handled by the motor controller by itself, don't bother.
If your concept of battery monitoring system is simple and straight forward, would be better.
It can be made more attractive with a large display connection on a VGA type of signal and better yet, touch sensitive control interface(USB)
Final customer choice of equipment, this monitors (7" and 8") are vast and very economic today days.
The small 4 line LCD modules are VERY difficult to read in a moving vehicle.

Just my 2 cents.

[nlc]

Originally Posted by mrbigh

A very realistic idea would be to go modular for add on specific and complex features.

It's exactly this way I see things

Originally Posted by mrbigh

The function of pre-charge and main contactor handling is better handled by the motor controller by itself, don't bother.
If your concept of battery monitoring system is simple and straight forward, would be better.

Yes, they actually implements this feature because precharge is mandatory and it simplify the user reflexion about that, but logically it's not the job of the controller to do that.
But you are right, today all controller manage precharge, thus it's not mandatory to implement it on the BMS.
But to really have a generic platform, in the case of a true calculator managing all the EV instead of just a BMS board, my idea is to have a generic calculator with multiple input/output, and each one can be configured between some function. It can be for example :
- Contactor/relay output, with pwm possibility to ajust the contactor voltage and burst/continuous current
- Analog input (current sensor, temperature, throttle, brake, etc...)
- Analog output ( to pilot the controller for example)
- Digital input (various type switch, speed signal,...)

I think more the board is generic, better it is, because with software the calculator can be integrated easily in all EV and propose powerful functionality.

Originally Posted by mrbigh

It can be made more attractive with a large display connection on a VGA type of signal and better yet, touch sensitive control interface(USB)
Final customer choice of equipment, this monitors (7" and 8") are vast and very economic today days.

Hum why not, it's a good idea, have you a link on this kind of display ?
From my side I was considering raw TFT screen + touchpanel, with integrated driver/framebuffer, we can now found very nice thing for very low price. Just need to add the backlight management (easy), and a LVDS serder to deport the microcontroller bus on the display with standard twisted cable as an ethernet cable.

Originally Posted by mrbigh

The small 4 line LCD modules are VERY difficult to read in a moving vehicle.

Just my 2 cents.

Hum, I think that we can just say that these king of screen are really really unusable for this usage
And a "big" graphical black/white display is more expensive that a beautiful color TFT screen !!!

[esoneson]

nlc,

Your contribution to EVs is much appreciated and making the protocol open is also commendable.

I have one question.

In the light of the "bricking" of the Tesla which is caused by leaving your vehicle alone for a long period of time with no way of "turning off" the drain on the traction pack, is there any state of the slave board where it does not drain any power? Can you "turn it off"?

This is the one characteristic that the slave board that is powered by the mother board that would enable total power off of the vehicle.

EDIT: sorry, that was a very poorly constructed English sentence.

Thanks, and great work in miniaturizing your slave board.

Eric