Ok, thank you very much, thus I can answer questions :
Alan B wrote:What technology do you use to communicate between the boards?
It's UART RS232 based : Tx of "master" board is connected to Rx of the top cell, Tx of a cell is connected to Rx of the next cell, and on the last cell (bottom cell), the Tx is connected to the Rx of the master. Each cell is connected to next cell with just one wire. Of course it's not RS232 level !
The master sends a request/command frame and the frame pass through each cell, and each cell concatenate their data to the frame and calculate new checksum. When the frame arrive to the master, it automatically knows the number of cell on the pack and gets the voltage and temperature of each cell. Also, because each cell is connected to the next cell, there is a automatic addressing of cells, absolutely no configuration at all on slaves. With this daisy chain functional operation, it's impossible to have a malfunctioning of one slave board and destroy the cell because the master will not receive any frame and can detect the problem immediately. In this case, to locate the problem it's very easy, just look where the LED doesn't flash on the pack and the problem is located here !
From communication speed point of view, if you imagine a pack of 255 cells, I can read all 255 voltage/temperature every 1.5s
bigmoose wrote:I'll throw out a question: Have you tested the system in a vehicle with a couple of hundred amps being slung around by the controller? Is the system immune to the EMI?
Not for the moment, but it will be the case don't worry about that, before sell anything there are still many test to do. And I plan the propose a preferential price for first people which want to try the system. For EMI, 2 things to take into account :
- The board must be maximum immunized, I think it's the case because design is simple, efficiency (and the high current don't pass through the board), but need to verify that
- In case of very powerful EMI spike, if the system or communication is perturbed, everything must restart correctly when the EMI spike is finished. For this point it's the case, the slave software is very robust, in case of communication problem everything is managed, and in case of big crash and freeze because of big EMI spike, board automatically restart, thank to watchdog timer.
They sure look pretty
How are they with vibration? A lower profile would probably make for a more robust system.
For the profile in my 10Ah pack it was mandatory for me to mount the pod this way, but normally the pod is inserted directly in the board edge. For vibration, my board is much smaller than every expensive commercial product which use same connection principle, so it can only be better ! But there is also the possibility to not use the pod for GND electrode and also use a wire, and directly stick the board to the cell.
mvly wrote:Looks slick, but does it balance? I would think that is also important other than monitoring it. It would do this only during charging.
Yes, it balances, the master can switch ON/OFF the balancing of any slave at any time
. It's not a big balancing (approx 200mA) because the board is small, but it's not really a problem because with all independent voltage of all cells, it become possible in the master to precisely determine the characteristics of each cell and then have a smart balancing which begin its work during the charge
and not at the end of charge when the cell reach the HVC threshold. But for those who think 200mA is too small current balancing, I put 2 big solder pad under the board to solder an optional external power resistor to boost the balancing current. The switch I use on the board can commute 4A
t3sla wrote:Brass tax.
How much we looking at $??
Brass tax ? Sorry I don't understood the expression, what does it means ?
The nude slave board price will be around 9€ (~12$ ?), and a little more if you need the pod and the screw terminal
In the next message I will give all the slave board technical specification