Really interested in bms solar, electronics microproceasors ect. I would like to build this bms could someone show me where the latest board is so i can buy it as i have many 18650s that need a home i have been trying to build a battery packs.
I have been a pcb deaigner could help in future with new designs if needed and help with design or hardware ect.
Am an expert in design spark, and protel, pcb packages Dos version, im old, could help with pcb advice ect.
Is now a final fully working design?
Or is there some of the latest boards for sale?
Wonder if someone could send a pm to
Chitu_Mihai-Georgehanks asmi am unable he has some boards for sale
Im so excited i wont be able to sleep tonight
Thank you
Hi @Andy do you get a voltage reading on the test point between that and cell negative? It should be about half the cell voltage.
Its strange that you are getting zero reading for both temperature and voltage - are the calibration values correct (if they are zero it would do this)
Does the web interface show the other voltages correctly?
It’s a huge difference and not compatible. Different components, power consumption, etc. As @stuart mention is nothing wrong with V3 but the project evolved and in V4 there are more possibilities. I did not build the V4, for the moment i will stay with the V3, but V4 looks very interesting!
hello stuart,
No i solved the temp and voltage problem. I found a short on the actual board and fixed the other short under the resister, so that took me to 13 boards working. I am now trying to get my 14’s working
This a new problem, 2 boards that I measure from gnd to each point on each of the components are the same as a proven good board, but these 2 wont provision. The wemos i working correctly. I have changed U2 several times as well. Thanks Andy
Okay, disconnect all the boards except the “bad one”. Reboot the Wemos (it only scans for modules on power up).
Can you provision the board now? If you can, select “factory reset” for that module and then try it again in the string with the others and see if you can provision it.
Software question: If I wanted to make some minor changes to the controller / GUI code, would I end up having to re-provision all the cells every time I flash the wemos?
I want to give you an experience report about my current v3 build. Just some things I run into and which were not so easy etc. Currently I have done 9 of 14 boards. They are all working now…!
I need the BMS for a Diy Powerwall made out of 1120 18650 cells connected as a 14s setup. The total capacity is ~10 kWh.
Also I just ordered stuff for the v4. Just for fun
I ordered most of the components via Aliexpress. To find the ATtiny85 was more difficult, at least at low cost!
I used hot air to solder the boards. No problem at all.
As discharge cement resistor I have chosen 10 W 2 Ohms as I have about 180 Ah (80 cells) in each pack. At 4,1 V (max. setting for me) the current flow will be ~2 A => ~8,5 Watts. Lets see if the resistors are really able to handle 10 W! As backup I have some 3.3 Ohms laying around. Of course I left a couple of mm space to the pcb not to heat up the whole circuit.
Programming work easily done. But I have done some Arduino projects before. I used an Arduino Nano which I flashed before as ISP. Burning the boot loader and writing the code went smoothly.
I use a NodeMcu ESP8266 ESP-12E as controller. First I didn’t read about the pull up resistors for SCL and SDA. And ofcourse nothing was working. But 2.2 kOhm between +3.3V and SCL and SDA works perfectly for me now.
The first problem occured around board 6. First all 6 were running on a 6s test setup. But suddenly one board dropped of. The green LED was flashing showing the “panic mode” then. I couldn’t reset the board as it was not shown anymore. Also reflashing didn’t help. After erasing the flash with the given Arduino expample code and reflashing it worked again. Took me a while to figure this out.
With board 7,8 and 9 more problems came. After flashing they all showed the solid green LED light. But provisioning didn’t work at all. So I started to reprogramm etc. No luck. After that I started to check the solder joints around the I2C isolater chip. I found out that 1-2 solder joints on each board were bad!!! So I hand re-soldered them. And that was the solution for that problem. I think my 3D print stencil is the problem as not enough solder paste comes through these tiny holes. Also the chip arms bend easly. Thus, they were not touching the pcb. But it didnÄt see it with my microscope.
The blue LED is very week with the updated 4.7 kOhms in series. I think 1-2k would be better. Or even lower. In earlier versions a 2.2k was given. What do you think?
About the v4:
I have chosen 5 W 3.6 Ohm cement resistors. I don’t want to have the heat on the board. Once the board heats up, the voltage devider which gives the cell voltage drifts. I tried this with my v3 just by heating the two resistors a bit with my hot air gun (like 80 °C). The voltage reading in the web interface went up about ~0.2 V!
I hardly found the LM4040BIM3-2.0/NOPB. At Farnell it is discontinued. Finally I fount it on Aliexpress. But 1 USD each and only 10 peaces together. Thus 20 USD for that …
Thanks to all of you working on such a great project!
Hello Seb
Thanks for your post, you helped me solve of problem i been having. It was point 8, had 3 boards that wouldnt work correctly, everything look correct and was even measured correctly. However your point showed me it could be the I2C chip and its legs, so i pressed down on the legs with my nail and did a scan using the BMS controller test software and finally it showed up. Did the same with the other and now i have spare boards. finally so thank you SEB.
Andy
Ha! Yeah! I saw your post and I was facing the same problem more or less. So I started checking and checking. I couldn’t believe that the solder joints were bad. They looked so perfect.