Hi all,
I'm a bit of a sucker for reusing otherwise perfectly functional pieces of electronics and today I finally opened my old xiaomi 20000mAh PD powerbank to investigate. It outputs 15V@3A and 20V@2A so it's 45W one. Good enough for everything from charging macbook air to powering TS100.
Anyhow, otherwise good powerbank is plagued by shitty cells used inside. Those are pouch ATL 4.35V cells, 2x10000mAh in parallel. Haven't used the powerbank thaaat much, maybe couple of dozens cycles, 50 max. At "higher" power levels (20+ watts) it barely gave out half the capacity before turning off. Now, testing cells directly on a bench (but still two in parallel), I do see enormous voltage sag even at 0.25C (from 4.3V to 3.6...3.5V already at 5A). IR is 50+ mOhm too...
Now I would have thrown them away and soldered 6 good 18650 cells as replacement without writing here if not the pesky high voltage cells originally used in this powerbank. Charging through the board I verified that it's configured to charge up to 4.3V. While there are some HV 18650 cells in existence, they are expensive and practically unobtainable in a shithole country I'm currently in.
So, me, a total noob, started tracing components on the board and searching datasheets online. Found out that the board uses Intersil 95538H buck-boost NVDC charger chip. Didn't find proper pinout for that chip, just
this diagram (it's for 95538
B, didn't find the H version at all). Seems that there are no external voltage dividers options for setting voltage levels as is sometimes done in that kind of circuits..
So.. any ideas how to repurpose the board to charge regular li-ion cells and limit charge to 4.2V? It would be weird if that charger chip wasn't configurable, but if and how is it possible to poke it? Preferably without desoldering it from the board. Anyone done something similar before?
I know it's not a lot of savings in terms of money, but I have some good ~3000mAh 18650 cells laying around and instead of buying another PD board and building a DIY powerbank I would really like to repurpose the old board and shell. 6x18650s would be exact fit there..
PS. added some pics of the board as attachments if that helps anything