It has 4 salvaged Lipo’s from a dead laptop battery pack in 2s2p config connected to a dc-dc stepdown giving me 5v and then wired to a usb port. Should be good for 5-6 phone charges.
It desperately needs a recharge port and a low voltage cut off but its a pretty good start for $1.20 worth of components
For reference or if you have identical sized mac lipos here is the stl I slapped together.
it’s about time for an upgrade.
3 years of abuse and its still going strong.
I have a phone with a damaged usb C port. This little mod allows me to see the charge state of the power bank, so I stop discharging it too far, and also displays the Current and power transfered. No more buying new cables every week! Now its just about tweaking that angle till its just right.
An Arduino pro mini is powered from the 5v regulator on Raw and the 3.3v Vcc supplies the SSD1306 screen. Current monitoring is achieved by reading the voltage across a 0.1ohm resistor on the negative usb port supply providing a 32.3mA resolution. Voltage dividers are used to monitor the battery voltages. There is NO current limiting or short circuit protection LOL yay.
There is provision in the early code for charging using a single 5v supply and switching between charging the high side and low side batteries. However more work is required on that circuit and a new enclosure will be required to fit it all.
The code was written a while ago but no major usage bugs have been found so far. It would be nice to include graphing, storing session data and storage capacity estimation. Which is leaning more towards a proper BMS and will prove handy for a future MPPT project.
Lots of work to do but at least I have a laughable Power Bank to take through airport security.
