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I've built the setup below for 2 Lithium-ion batteries in series:

My setup

The battery balance module is an FDC-2S-2 (I can't find a datasheet, weirdly): fdc-2s-2 module

Problem: Even though I read 7.5 V between B+ and B-, I read 0 volts between P+ and P-. I tried to power an Arduino and I also tried to power a single LED with a resistor. Nothing worked in both tests. I have 2 of these modules and 4 batteries in total. I tested the second module with 2 different batteries but it gave 0 V too.

My goal is to power an Arduino which draws 20-60 mA with its sensors. I'm looking forward to solve the issue with your help.

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1 Answer 1

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I figured it out, there is that weird thing about some BMS modules that they need initial charging, even for just one moment, to start operating.

Basically BMS comes off dead and you wake it up by plugging in the adapter to P+ and P- pins and then you can remove the power adapter right away, the BMS will start operating and you will see battery voltage at across P+ and P-

If you remove the batteries and don't connect any adapter, the BMS will die again and you won't see voltage at the output when you connect batteries, you must then redo the charging thing and Boom the BMS is awake again.

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