Maciej Grela's Second Life UPSes Find a Use for Faulty Network Switches, Old Hoverboard Batteries

Maker Maciej Grela has been on an unusual upcycling journey, aiming to help his home lab's uptime while also saving electronic waste from ending up in a landfill — by turning the cases from old rack-mount network switches and old hoverboard batteries into do-it-yourself uninterruptible power supplies (UPSes).

"I have decided to build a UPS that would power my home network equipment rack using lithium-ion 18650 cells," Grela wrote at the start of the project, building what would become known as the Second Life UPS Mark I. "[It] should fit the equipment rack in a 1U format [and] it should provide 12V DC, 5V DC, as well as 230V for the switch."

There is, of course, a family of devices which already comes in a chassis perfectly sized to slide into a 19" rack: network switches. Taking an old 24-port 19" 10/100 switch, long retired and headed to silicon heaven, Grela gutted the chassis and set about filling it with replacement hardware: a power supply, a battery management system, output connectors, and as many 18650 lithium-ion batteries as the space would support.

"The battery for the UPS was built using 18650 Li-ion cells recovered from hoverboard battery packs," Grela explains. "These are cheap no-name cells with not a lot of capacity left in them (around 800 mAh) each but I figured that a UPS would be the perfect idea to utilize them. They will operate under low current load per cell so their internal resistance shouldn't be a problem. The UPS will be mostly sitting idle and charged so the cells won't get further capacity fade from cycling."

Having successfully built and tested the first-generation Second Life UPS, Grela set about making another — targeting increased battery capacity, a higher power output budget, a simpler circuit, and a modular layout which would make it easier to customize in the future. "One disadvantage of the previous Second Life UPS design was the fact that the front connectors where loads can be powered were placed on hand-made breadboard PCBs," Grela explains.

"After some thought," Grela continues, "I have decided that this approach makes the design hard to replicate and adapt. To improve this I designed a number of standard sized PCBs that host common load connectors and fuse sockets. All of the PCBs fit into cutouts in Ethernet switch enclosures hosting 4×2 Ethernet ports. This is the most common cutout size in an Ethernet switch and it allows a user to mix and match modules based on their needs."

Using another surplus switch chassis, the Second Life UPS Mark II hosts an impressive 96 cells with a 600Wh capacity — yet, because the batteries were salvaged, comes in at under €70 (around $77) for the off-the-shelf components required.

Grela's website hosts the full project write-up, along with schematics for those who would like to build their own Second Life UPS.