Show threadRommudohJul 10, 2025
Here are a few more boards, one for 4S and two for 3S. The last one is attached to a triple 18650 battery holder and will be tested with real cells soon. So far all tests look fine.
The 4S and 3S LiIon were soldered using hot air and solder paste (except the MOSFETs, those were already soldered using a normal iron). This was a very pleasant experience and I will use it more often.
#soldering #diyelectronics #BMS #lithiumbattery #18650 #BQ77915 #hotairsoldering #solderpaste
Show threadRommudohJul 5, 2025
And I finished #soldering the first #BMS board. It's configured for a 5S LiIon #battery with 5A output current limit.
Here the finished board and the test setup.
So far, it works as intended. It cuts discharge at 4.91A, or when battery voltage drops below 14.5V. Charging is disabled when voltage gets too high.
I'll still have to test the temperature behavior, and how balancing works.
When I'm satisfied, I'll try with real cells.
#diyelectronics #BQ77915
RommudohJul 4, 2025
My #BMS #PCBs arrived from @aislerhq and they look nice. I designed it because I couldn't find 3S BMS for #LiFePO4 cells and didn't like the voltage thresholds of the cheap #LiIon ones.
It uses the #BQ77915 chip from #TexasInstruments. Size is 63x50mm.
While fetching all components according to the BOM, I noticed the #diode had the #footprint SOT-323 assigned. I only have SOT-23 ones  
I'm glad that I can still make it fit, and the third leg isn't used at all (it's a single diode).
Can't wait to find some time to finish soldering a few and try them out.
It supports 3S up to 5S, and I added #silkscreen part to mark how it's configured.
The back has detailed instructions, so I don't forget them.