PowerBank Hack ?

[ichiban]

I recently bought some powerbank cases with charging/discharging circuit included. They are cheap and useful to utilize our spare 18650s.


Dual USB 8*18650 Power Bank Battery Box Mobile Phone Charger DIY Shell Case :

https://www.aliexpress.com/item/Rovtop-Hot-sale-5V-Dual-USB-8-18650-Power-Bank-Battery-Box-Mobile-Phone-Charger-DIY/32911402208.html?spm=a2g0s.9042311.0.0.7cef4c4dIPSv9C



Some monks I know had to hike over a month into deep jungle for their monkhood activities. They normally use small powerbank to charge phones (for gps) and 2-3 LEDs flashlights for 5-6 peoples and it never lasted a week. Spare batteries are expensive, heavy + no where to charge. When power ran out, they have to make fire afterwards. So I made them one giant 50,000-mAh (1S24P) powerbank from old laptops-harvested 18650s, was afraid that it won't last a month.




View attachment 4



Time was short as parts just arrived that evening and I had hours to finish it from scratch. Not enough time to do much - but manage to wrap it up just in time.

Many of the cheap similar powerbank kits use the same pcb board which is easy. One thing bugging me for a while, I found later that the circuit LV cut-off is around 3.5-3.6V which is too high since there is still some juice left. In this case, we really need to squeeze the remaining power out of the only powerbank available.

Spec (rough) :
1SXP (all parallel) cells
O/P : 5V @2.1A & 1A
over current and short cct protection
BMS not needed since only 1S





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Is there a way to mod it to have LVC 3.0-3.1 V. or even lower (for next charity units) ?
May be next time I'll have to make 100,000mAh.. with wheels on it :lol:

Any idea for this application will be appreciated.

 

[amberwolf]

If you find the pinouts for the chips, and determine that one of them is a "BMS" chip, then it may have a separate input pin for monitoring cell voltage.

If it does, and if that pin has a voltage divider on it, you can change the ratio to change the LVC, but it will also change the HVC (lowering it, too).

If it has no voltage divider on it, then you can't alter the LVC cuz it's sensed directly. (unless you can find out how to program the chip, if it is programmable (probably is not)).

If it's using a discrete chip (op-amp, etc) as the LVC, you can find the voltage divider or feedback / etc and change it's ratio. Same stuff applies as to the BMS chip pin--it's probably for LVC and HVC, so would probably change both. But if there are separate circuits for each....

 

[ichiban]

Thanks for the reply amberwolf

I thought people have already gone to celebrate their Christmas.


Merry Christmas & Happy New Year
to everyone here on ES.


I will have to check out what you recommend carefully since I believe there will be more of the big powerbanks for me to make. Your method is straight forward but not very easy to do. :?



Thank you again amberwolf.

:thumb:

 

[fechter]

I did something similar in the past. It takes a really long time to fully charge but works great.
You might try just getting a different power bank board and it might have a lower cutoff. Those things are pretty cheap now.

 

[ichiban]

I did something similar in the past. It takes a really long time to fully charge but works great.
You might try just getting a different power bank board and it might have a lower cutoff. Those things are pretty cheap now.

Yes fechter, they are really useful especially on the go. I am thinking about making a portable power unit, with output like ac plug starting at 800 wh or so. That will be great for camping. I got an old UPS laying around so that'll be a good start.

Let's see if I can find some other circuit board with low voltage cutoff like you recommend for the Power Bank kits.

Happy riding everyone in the coming years !!

 

[fechter]

I have a 600W inverter that was made for 48v but works great on my 52v bike battery. That battery is almost 1kwh and is in a handy 50cal plastic ammo can.