I'm building a small robot (for the context, with a pi zero, a PCA9685 motor controller, 8 small servo motors a regulator and an Ubec) fully powered from a 2S 18650 battery.
I've inserted a (cheap) 2S BMS between the (homemade) battery pack (with a small power switch included, and removable 18650 batteries that I remove to charge from an external charger) and the rest of the electronics. My problem is that unless I put some voltage to BMS output (P+ and P-, which are also used when charging) to "boot it up", the BMS refuses to output anything. Once "booted", I can remove the voltage.
I've seen people talkinging about "reseting" or "activating" BMS by charging it in order to make it output current… However I don't want to include a charging plug in my battery pack since I want them to be removable (as I'm too lazy and don't trust much these BMS for charging, since they don't seem to do balancing)…
So is there a way to workaround this "activation" step so that I can just switch on my battery power button and it works?
For reference I've tried with these 2 BMS but had the same issue:
https://www.aliexpress.com/item/32827942991.html
https://www.nkon.nl/sk/k/2S-BMS-PCB-2MOS-2004-D.pdf
Thanks for your help
Best Answer
The simplest workaround to an un-activated BMS (sleep mode) is to supply it with power from it's own batteries. To achieve this, a push switch/momentary switch can be used between the P- and B- terminals of the BMS.
Note: This will work only if the cells have adequate voltage. The BMS will return to sleep mode if the individual voltages are too high or too low.