Isaac Porras (Solarcycle) describes his Power Stacker as a “portable, modular, and configurable USB rechargeable lithium-ion battery pack system,” which can be combined for increased power, or separated for use in several smaller projects. A lot of us have one or more USB rechargeable power packs for charging mobile devices or to power projects in the field, as they are cheap and easily implemented.
Chances are, if you crack one of them open, you will find it packed with a few 18650 lithium-ion cells and a 5V converter for USB charging — a simplistic and ingenious design, but a fallible one. Once the cells can no longer hold a charge, and reach end-of-life, they can’t be replaced, and they weren’t designed to use in tandem for increased power output. That’s where Porras’ Power Stacker comes in, as it can be tailored to your power requirements, and the cells can be swapped out for new ones when they can no longer hold any power.
Under the hood, the Power Stacker features a Maxim MAX8903 lithium-ion controller assigned to each battery (Panasonic NCR18650B 3350mAh) in the system, which allows for each to be charged to their correct voltage. The platform also packs a 5V DC-DC converter, along with a protoboard backplane that enables multiple boards to be connected.
As far as specs go, the Power Stacker can be fully charged in three hours (3350mAh @ 5W)/7-hours (13400mAh @ 8W), has an input current of 450 to 2600mA (voltage: 5 to 6V), and an output current of up to 2000mA with 3.6V direct or 5V with DC-DC converter.