SparkGen: The Weekend Thermoelectric Generator

SparkGen is designed as a rugged, portable generator that burns twigs and branches to produce electricity. It uses a tuned rocket stove design to maximize combustion efficiency and concentrate heat onto a bank of TEG modules. A custom heat sink with forced air cooling maintains the cold side. The output is regulated to 5V USB and 12V DC. The build is segmented into two days: Day 1 focuses on fabricating the stove body from a steel can, cutting and assembling the chimney, and mounting TEG modules with thermal paste. Day 2 involves wiring the modules, building the heat sink fan, integrating the buck converter and USB charging circuit, and testing. No welding is required; only rivets, bolts, and high-temp epoxy are used. The design is modular for easy part replacement.

Off-grid power options are often heavy (solar panels) or noisy (gas generators). A twig-burning generator is ultra-light fuel, silent, and works at night. Existing DIY TEG stoves are inefficient and visually unappealing. SparkGen aims for a clean, repeatable design that can be built in a weekend.

• Achieve 15W continuous electrical output from a wood fire.\n- Complete build in under 48 hours from scratch.\n- Use only scavenged or off-the-shelf parts (no CNC or custom fabrication).\n- Provide USB-C Power Delivery and a 12V barrel jack output.\n- Compact enough to fit in a backpack (stove body < 1 gallon).\n- Safety features: double-walled chimney, cool-touch handles, and over-temperature shutoff.

• Not intended as a permanent home installation.\n- Not designed for high power (>50W).\n- Not a precision temperature control system.\n- Not a polished consumer product.\n- Not a wood-gasifier; it's a simple rocket stove.

• Materials: 1-gallon steel paint can (stove body), 4-inch diameter steel chimney pipe, high-temp insulation (rockwool), TEG modules (e.g., TEC1-12706), large aluminum heat sink, 12V DC fan, boost-buck converter (5V/12V), USB-C PD board, switches, wiring, high-temp thermal paste, rivets, high-temp paint.\n- Tools: Angle grinder, drill, rivet gun, multimeter, soldering iron, files, lumber for jig.

The rocket stove design features a horizontal fuel feed and vertical chimney. TEG modules are sandwiched between a hot plate (steel plate on top of stove) and a heat sink with fan. The hot side reaches ~300°C, while the cold side is kept below 70°C by forced air. Modules are wired in series, producing ~12V at low current. Power electronics step up/down to stable 5V/12V. No battery is included in the weekend build, but the output can charge a power bank.

• Thermal runaway if fan fails, damaging TEG modules.\n- TEG modules cracking from thermal shock during first heat-up.\n- Poor thermal contact reducing efficiency.\n- Fire hazard if insulation is inadequate.\n- Time overrun if parts don't fit (e.g., heat sink mounting).

• Optimal stove size-to-TEG area ratio for 15W?\n- Fan speed control: PWM vs simple on/off?\n- Should we add a small Li-Ion battery as a buffer?\n- How to test indoors without smoke? (Maybe a propane burner for dry run)\n- Best source for cheap TEG modules rated for repeated thermal cycling?

I sketched the plans and bought the steel can and heat sink, but then a demanding work project consumed all my weekends. The idea still sits in my workshop drawer, waiting for a clear two-day stretch.

Future extensions could include a battery management system, a small OLED display showing power and temperature, or using the stove for cooking while generating power.