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Question: I made a power pack of 18650s with protection board. Is voltage drop normal? Answered

I made a power pack using 18650 batteries from an old laptop. All batteries tested individually are good. 4 batteries in 2S format. I used a cheap 2S 3Amp rated protection board I got on Ebay from China. I correctly connected all the terminals and properly soldered, B+/B- to the +/- of the final ends of battery and BM to the middle.

The voltage measured directly at the battery terminals (at B+/B-) is 8.4 volts but at P+/P- (the input/output terminals of the board) it measures 7.5. Which means this board will not produce more than 7.5 volt usable voltage even when the batteries are fully charged to 8.4. Is that expected and normal? or is there a problem with the board.

Thanks for help.


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2 years ago

A slight voltage drop is quite normal here.
Question is wether or not this will impact on the performance.
The board is between battery and output and even if it would be just a single protecting diode - it would cause a slight voltage drop of about 0.7V already.
Anything making sure the battery is disconnected under unsuitable conditions will need a certain amount of voltage but hopefully only a mA or less to operate.