Power station for my work desk

My desk used to have a separate charger for everything: laptop, phone, tablet, LED strip, clock, etc. I replaced them with one box: a 4S LiFePO4 battery with USB-C/USB-A outputs and a wireless charger on top. It also works as a UPS: when mains power goes out, everything keeps running from the battery, and the whole battery capacity is usable.

Front: BMS and old relay buttons, QC USB-A/USB-C, banana jacks

Back: USB-C, USB-A, XT60 and charger input

How it works

    flowchart TB
  PSU["Laptop charger<br/>20 V 3.25 A"] --> UPS["UPS 1228-12<br/>charge 5 A / 14.2 V<br/>output 20 V"]
  subgraph BAT["Battery"]
    PACK["4S EVE LF22K<br/>12.8 V 22 Ah ≈ 282 Wh"] <--> BMS["JK BMS"]
  end
  BAT <--> UPS
  UPS -- 20 V --> USBA["USB-A 4-port module"]
  UPS -- 20 V --> USBC["USB-C PD 65 W modules"]
  UPS -- 20 V --> QC["QC Type-C/USB-A module"]
  UPS -- 20 V --> QI["Wireless charger 15 W"]
  BAT --> RAW["XT60, banana jacks"]
  BMS -- GPS port --> BUCK["MP1584 buck"] --> ESP["ESP32"]
  BMS -- "GPS port (UART)" --> ESP
  ESP -. Wi-Fi .-> HA["Home Assistant"]

UPS module is the heart of the build. It charges the battery (5 A, up to 14.2 V, i.e. 3.55 V per cell) and switches the load between the charger and the battery. Its output is set to 20 V, which feeds all USB modules and the wireless charger.
Charger is an old 20 V 3.25 A (65 W) laptop charger, plugged into the DC barrel jack on the back. It doesn’t really matter which one, as the UPS module handles charging. 65 W is a compromise, I just used what I had: when the charger is plugged in, power goes to the load first and the rest goes to charging. I don’t have a constant 65 W load, so the battery still charges.
BMS protects the cells and balances them. A button on the case turns it on and off.
XT60 and banana jacks are connected directly to the battery. The banana jacks power the LED light of my desk (on a cable with an inline switch).
ESP32 reads the BMS over its GPS port and sends data to Home Assistant. The same port powers it through an MP1584 buck converter.

Parts

Part	Details
Battery	4× EVE LF22K 22 Ah, B-grade, in series (4S)
BMS	JK BMS BD4A8S4P
UPS / charger board	UPS 1228-12
USB-A	4-way PD 65 W Type-C/USB-A module
USB-C	D65W fast charging module
QC module	QC4.0/QC3.0 USB Type-C
Wireless charger	15 W wireless charger transmitter module
Monitoring	ESP32 + Mini MP1584EN DC-DC buck converter
Enclosure	MiBox MB-43, plus my own 3D-printed battery frame and back panel

The cells are B-grade, which is why they are cheap. So far they behave well: after 92 cycles the cells are within 9 mV of each other (see Monitoring).

EVE LF22K specifications

Parameter	Value
Chemistry	LiFePO4
Nominal voltage	3.2 V
Capacity	22 Ah
Standard charge / discharge	22 A (1C)
Max charge / discharge	66 A (3C)
Voltage limits (min / max)	2.5 V / 3.7 V
Terminal type	M8
Dimensions (H × W × T)	131.8 × 148.2 × 17.7 mm
Weight	628 g

The pack is 4 cells in series: 12.8 V nominal, 22 Ah, about 282 Wh.

Monitoring

The ESP32 runs ESPHome with syssi/esphome-jk-bms, connected to the GPS port of the BMS (UART-TTL):

substitutions:
  name: power-station-workdesk
  device_description: "Monitor a JK-BMS using the GPS port (UART-TTL)"
  external_components_source: github://syssi/esphome-jk-bms@main
  tx_pin: GPIO16
  rx_pin: GPIO17

The rest of the config is the example from the repository. In Home Assistant I get state of charge, power, cell voltages, temperatures and cycles:

History

2023: first build

The BMS was first powered in November 2023. Since then the pack has done 92 cycles, about 2,000 Ah in total.

2024: initial version

The BMS, buck converters and banana jacks were all mounted on top of the battery.

Before the PD modules, the USB ports were powered by Mini MP1584EN buck converters and mounted in metal round socket modules. A relay switched the whole load on and off with a single illuminated button. The button is still on the front, but it’s not connected anymore.