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200 Ah power station from four 3.2 V prismatic LiFePO4 cells: 4S BMS, 2 × 12 V, 3 × USB, mains charger

Bench build · Batteries and solar · Intermediate · about 90 minutes

12.8 V 200 Ah (2560 Wh) power station from four prismatic cells with a 4S BMS, two fused 12 V outputs, three USB outputs, a watt meter and a 20 A mains charger. A 12 V 200 Ah portable power station built from cells. Four prismatic LiFePO4 cells (3.2 V 200 Ah, 640 Wh each) in series make 12.8 V 200 Ah, 2560 Wh. A 4S 100 A balancing BMS on the negative side watches every cell: it cuts charging at 3.65 V on any cell, cuts the load at 2.5 V, and balances near full. The output board: an F1 125 A MIDI fuse on the pack positive, M1 (a DC watt meter: volts, amps, watts and the Wh taken since switch-on), S1, a 30 A rocker as the master switch (the MIDI fuse does the protecting: a breaker here would trip magnetically on any output short and take the whole station down with it), then two 12 V jack outputs at pack voltage (12.0 V empty to 14.6 V on the charger, the same range as a car’s socket: a 12 V accessory has to take that, and the cheap LED bulb here runs hot while the charger is on), each with a 5 A blade fuse (here one lights a 9 W 12 V bulb, the other runs a Wi-Fi router through a plug), and three HW-688 USB outputs (5.2 V up to 5 A each) behind 3 A blade fuses, a phone on each. Charging: a 14.6 V 20 A LiFePO4 mains charger on the pack terminals (CC/CV, stops at 2 A, restarts at 13.4 V); 20 A is 0.1 C, about 10 hours from empty. The readings panel shows the runtime at the load of the moment: the whole station busy (three phones, bulb, router, about 60 W) runs for about 38 hours, the router alone for a week.

200 Ah power station from four 3.2 V prismatic LiFePO4 cells: 4S BMS, 2 × 12 V, 3 × USB, mains charger: the finished build running on the simulator's bench

Build it in the labGuided build, test sheet and fault finding, free in your browser.

Parts list

Test procedure

Each test has an expected value and a pass range, like a factory test sheet:

  1. The 12 V outputs sit at pack voltage
  2. 12 V output 2 runs the router
  3. USB 1 charges its phone at 5 V
  4. Whole station on the pack: three phones, bulb, router
  5. Runtime at that load from full
  6. The charger pushes 20 A into a half-empty pack
  7. The charger backs off on a full pack
  8. A dead short on output 1 blows its fuse, not the station
  9. Cells share the load evenly
  10. One flat cell: the BMS cuts the load, the station goes dark

How it works

What it does: 12.8 V 200 Ah (2560 Wh) power station from four prismatic cells with a 4S BMS, two fused 12 V outputs, three USB outputs, a watt meter and a 20 A mains charger.

Build it (guided or ready-made), then run its test procedure below. Every test has an expected value and a pass range, just like a factory test sheet.

Background

Prismatic cells (EVE, CATL, REPT) are what the big "DIY LiFePO4" banks are built from: four cells, a BMS, compression plates and busbars, at a fraction of the price of a finished battery of the same capacity.

More builds: batteries and solar