I built an electric bike battery with the DIY BMS. I have used it for 2 weeks and it has been great, but now it has become unreliable. It started with I couldn’t get the battery to power up, now I have on a test bench, and it does power up, but it shuts down when I turn off the bike motor button.
My circuit
I am not a professional, if there is a better way to turn on and off the DC-DCs and controller, please let me know. I just can’t understand why it has worked great and now is just not working.
The Arduino Nano represents the BMS controller, and I am using one of its relays to control the low voltage cutoff. The motor relay is a 12v car relay that can handle 30A.
The motor can take 30 amps max, the battery is a 17s li-ion with 18650s 7 in series. I am running it from 51v to 68v.
Swapped out the controller board but not the ESP32 still it is acting strange and cutting the board’s low voltage relay, even if the battery is fully charged. No error messages. Info on the version:
Platform & Version
Host name:DIYBMS-004ED7B4
Processor: ESP32
Version: 4d240d0120df636fbe0bf136d1db2aa3e0a35694
Compiled: 2022-09-06T10:32:56.505Z
Language: en
SDK Version:v4.4.1-1-gb8050b365e
Min free Heap:139344
Free heap:158556
Heap size:294324
I finally figured out why the rules were not working so well, I needed to add a fly back diode for the relay, even thought I had a DC-DC between the relay and control board it still made the controller go crazy.
You should check that the switching device has not been damaged by the excessive voltage it experienced when switching off. You always need the diode to catch and circulate the current resulting from energy that was stored in the magnetic field, it has to go somewhere or damage is a likely result.
