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Rechargeable 12 V bulb on two 32700 LiFePO4 cells: 2S BMS, USB-C 2S charger and a 12 V boost

Bench build · Everyday gadgets · Beginner · about 30 minutes

A brownout bulb that charges from USB-C and lights a room for an evening. Two 32700 LiFePO4 cells in series make 6.4 V (6 Ah, 38 Wh). A 2S BMS protects them, a USB-C 2S charger board set to LiFePO4 fills them to 7.3 V from any phone charger, and an XL6009 boosts the pack to a steady 12 V for an ordinary 12 V LED bulb, so the light stays the same brightness until the cells are empty. A 9 W bulb runs about 3½ hours.

Rechargeable 12 V bulb on two 32700 LiFePO4 cells: 2S BMS, USB-C 2S charger and a 12 V boost: the finished build running on the simulator's bench

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

zencircuitlab.com/l/rechargeable-12v-bulb-two

Parts list

Test procedure

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

  1. On battery: bulb voltage
  2. On battery: current from the cells
  3. Switch off: charge current
  4. Full: stops at 7.3 V

How it works

What it does: A brownout bulb that charges from USB-C and lights a room for an evening.

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

Sold as “emergency bulbs” and “rechargeable camping bulbs”, usually with one small cell; two 32700s last several times longer and survive thousands of cycles.

More builds: everyday gadgets