Universal 3S Li‑ion Power Pack for Metal Detectors

A simple and compact 3S Li‑ion power module designed for metal detectors that use a Teknetics‑style armrest mount. With an adjustable step‑down converter, it can also power any device that normally runs from 9 V, or any voltage within the converter’s range.

The design is modular, serviceable and easy to print. Ideal for users who want to replace a classic 9V battery with a modern 3S Li‑ion solution.

Compatibility

Mechanical

Fits detectors with the Teknetics‑style armrest mount, including:

• Teknetics G2 / G2+
• Fisher Gold Bug Pro
• Teknetics Alpha / Delta / Gamma
• All G2‑like clones
• Any detector using the same armrest geometry

Electrical

• Adjustable output (typically set to 9 V)
• Suitable for any device within the step‑down module’s voltage range
• Can be used as a general‑purpose 3S Li‑ion power pack
   

Print Settings (PETG)

• Layer height: 0.2 mm
• Infill: 15%
• Perimeters: 3
• Supports: yes (only under the internal module‑separating slots)
• Brim: no
• Orientation: all parts printed vertically

• All parts fit on a single build plate

   

Bill of Materials (BOM)

• 3× 18650 Li‑ion cells (flat‑top)
• 3S BMS, 20 A (58×20 mm)
• MP2307 step‑down module (12×18 mm)
• Rocker ON/OFF switch (panel cutout 19×12.5 mm)
• 3.5 mm stereo panel‑mount jack – standard type, can be replaced with another connector if needed
• Panel‑mount charging connector (7.8 mm hole) – universal hole size, works with multiple DC connector types
• 470 µF/16V electrolytic capacitor – common value, other similar values also work
• Power twin‑lead cable + shielded stereo cable – length and gauge depend on the detector setup
• 2× rubber grommet (5 mm hole) – the hole is a base size; can be enlarged with a drill to fit any grommet
• 2× screws for the cover (M3 or small self‑tappers) – anything that fits the printed holes is fine
• 4× M5×15–20 mm screws and nuts for clamp
• Nickel strip for battery pack (thickness not critical)
• Rubber grommet (any size that fits the hole)
   

Assembly

1. Print all parts – all components are designed for vertical printing and fit on a single plate
2. Build the 3S battery pack – spot‑weld or solder the 3× 18650 cells into a 3S configuration. Connect the cells using thin nickel strip. Solder the balance wires (B1, B2) and main leads (B+ / B–) – route the balance wires through the battery slots before connecting the BMS
3. Connect the BMS – connect B+, B–, B1, B2 to the pack – the BMS output (P+ / P–) is used for both charging and powering the detector
4. Wire the charging connector – connect the BMS output directly to the panel charging connector – ensures the pack is always charged through the BMS protection
5. Install the rocker switch and step‑down module – from the charging connector, route the positive lead through the rocker switch – from the switch output, connect to the step‑down input – the negative lead goes directly from the BMS output to the step‑down input
6. Install the audio jack – the 3.5 mm jack is simply bridged (straight‑through connection) – it does not interact with the power circuit
7. Solder the output power cables - solder two 0.5 mm² power wires (positive and negative) that will go to the detector. Route them through the grommet toward the enclosure exit. These wires will later connect to the detector’s power input
8. Solder the shielded stereo cable for the audio jack - use a shielded stereo cable. Left and right channels are bridged (joined together). Connect the bridged signal to the jack’s tip/ring. Route the cable through the grommet toward the detector.
9. Add the 470 µF/16V capacitor – solder the capacitor to the step‑down output – alternatively, place it directly on the output cable going to the detector
10. Close the cover and secure it with screws 
11. Attach the module to the detector armrest – use 4× M5 screws, 15-20 mm length and 4x M5 nuts

Notes

• The design is not waterproof — intentionally, to keep it simple and serviceable.
• The slots are sized for the listed modules.
• Connector holes are universal and can be adapted if needed.