Power Bank

Overview

A power bank stores energy in lithium-ion cells and hands it back out over USB to charge phones, tablets and laptops away from a wall socket. This model packs three Li-ion Cell, 18650 cells into a Li-ion Cell Pack inside an extruded Aluminium Shell with moulded End Cap end caps. A single Main Board does the real work: it pulls energy from the cells, converts it to whatever voltage the attached device asks for, and pushes it out the Port Panel. The same USB-C port also runs in reverse to recharge the bank itself.

The pack carries 20,000 mAh at the cell voltage, about 74 Wh, enough to refill a phone several times or top up a laptop once. A Fuel Gauge + Button on the side shows the remaining charge as a row of LEDs when the button is pressed.

How it works

The three cells in the Li-ion Cell Pack are joined by spot-welded Nickel Strip strips and watched by a BMS Board, which balances the cells, cuts off on over- or under-voltage, and reads an NTC Temperature Sensor so charging backs off if the pack runs hot. Cell voltage swings from roughly 4.2 V down to 3.0 V as the pack drains, so a fixed regulator would not hold a steady rail. The Buck-Boost Converter converter on the Main Board handles that: it steps the cell voltage up or down as needed, delivering a clean output even as the cells sag, and runs the same way in reverse to charge them.

When a device is plugged in, the USB-C PD Controller negotiates a USB Power Delivery contract, agreeing on a voltage and current the device can accept, while the supervisory MCU sets the converter and steers the power-path MOSFETs. The whole loop clears about 90% efficiency, so most of the stored energy reaches the device rather than turning into heat in the aluminium shell. Pressing the Power Button wakes the bank and lights the gauge LEDs to show how much charge is left.