External light for underwater photography (For Olympus TG-6)

This is my latest attempt to make things watertight for recreational scuba diving. I used most of the knowledge from my previous article and summarized everything in this video:

Consider your skills before you start working on this project. Some experience with making watertight 3D prints and working with electronics may be useful. The whole setup requires buying some expensive parts and any mistake could cause a leak and damage to them.

Main specs

• Watertightness tested up to 46 m (138 ft) depth
• The whole setup consists of two identical lights
• High power LED (12000 lumen, 3500 K, 137 W, 115°)
• 3x 18650 batteries power the whole set
• LED powered by step-up DC converter
• The setup is controlled by magnetic switches with no need for moving parts
• Power modes: 0%/25%/100%

Main issues

Note that some features need various adjustments. This is still a prototype and although it works, it is not intended for mass production as it showed several malfunctions. If you decide to make the light yourselves, consider improving the following issues:

• This set doesn't use any battery management system. I haven't used this because I didn't have much time to redesign the battery case. The 18650 batteries are directly connected to the step-up converter. I calculated the approximate times until the batteries would get depleted (approx. 66 min at 25% power, 16 min at 100% power) and changed them between the dives. However, this is unsafe and I strongly recommend using a BMS.
• Consider adding some switch between the PSU and battery pack. To control the set with magnets, I had to “hack” the step-up converter. When the light is off, there is still a very small current going through. Leaving the batteries inside for a long time may damage them.
• The connectors at the battery pack I used are weak for the high currents. I suggest redesigning the battery pack and using something stronger as these may heat up a little at full power.

Used printers and materials

• SL1S SPEED with Prusament model resin alabaster white and Loctite 3843 resin
• MK3S+ and MK4 with Prusament PETG
• All printer and material settings are at .3mf files attached here.

Required electronics and other materials (for one light)

• 1x LED (CREE LED CXB3590-0000-000N0HCD35G)
• 1x Heat protector thermostat (90 °C bimetal closed thermostat with 15×7.2×3.8mm dimensions). I used a BH-B2D ceramic, bimetal 250V/6A thermostat. When the thermostat gets heated to 90 °C, it opens the circuit and stops powering the LED to prevent overheating.
• 4x Flat heat pipe 100x8.6x1.5 mm (WAKEFIELD THERMAL 120231)
• 1x Step-up DC-DC converter (this worked fine for me but a converter with stronger output power might be better)
• 2x Magnetic reed switch (any kind, only a very small current goes through)
• 3x 18650 single battery holder (just for salvaging the metal connectors - I recommend searching for a better method)
• Power cable (for connecting battery pack, PSU, and light)
• Solid copper wire (for connecting inner parts of the battery pack, PSU, and light)
• 3x 18650 batteries with the highest possible discharge current (at least 12 A). I recommend Sony VTC6 (3Ah and 30A discharge current)
• 2x 2x10mm golden banana plug (both males and females) - available at any hobby RC store
• 4.7 kOhm ±1% and 8.2 kOhm ±1% resistors
• Heat conductive paste
• 3x O ring 47x2.3 mm (or similar dimensions, I suggest visiting a local store and testing how it fits)
• Circular plexiglass cover (63.4 x 5 mm)
• Ecoflex 00-50 silicone (or any other silicone with high viscosity and good temperature resistance)
• Superglue (with activator)
• Epoxy glue (optional) - this can be used if you don't want to work fast with superglue
• 4x 25x3 mm (or longer) bolts with a conical head + 4x3 mm nuts (stainless steel is recommended)
• Some stainless steel 5 mm bolts and nuts if you're going to use my arms (however, I recommend designing something better)
• 1x 20x3x6 mm magnet for the switch
• Fine sandpaper
• Silicone grease (for O-rings)

Assembly

Most of the assembly is summed up in the video linked above. Here's just a short list of tips you may find useful.

• When working with silicone or any other glue, always keep all glued surfaces clean and degreased
• It is strongly recommended to debubble silicone or epoxy glue with a vacuum. Any large bubble may pose a risk of leaking
• I prepared channels at every joint for glue. These channels are best filled using a syringe, however, you may need to make an adaptor between the syringe and the opening. Even so, be prepared for a very dirty work with silicone.
• Don't forget to measure the wire length according to the arm length.
• Some external protective tubing for the wires is recommended.
• The battery pack is designed for re-using metal parts from factory-made 18650 battery holders. These need to be sanded a little for everything to fit properly (see the photos). However, I recommend you completely redesign the battery pack, or, at least, find stronger metal connectors suitable for high current.
• The battery pack with the battery case is designed for easy opening and connecting. There are supposed to be two golden pins for easy (dis)assembly.
• Probably the most difficult thing is setting the step-up DC converter and soldering the magnetic switches. Again, I recommend you find a suitable solution yourselves as my setup may be dangerous, and with any mistake, it might lead to damaging the electronics. If you decide to do it my way, below's the wiring of the DC converter with magnetic switches. When the first switch is on, the LED is off. When the second switch is on, the LED shines at 25% power. When both magnetic switches are off, the LED shines at 100% power.
• Carefully bend the coil to access the electronics, then unsolder the bottom blue potentiometer. Use the three free potentiometer pins and solder one magnetic switch and 4.7 kOhm resistor as shown below. Then, connect the next magnetic switch with an 8.2 kOhm resistor to the chip in the middle of the board. It is important to connect it properly to the pins as shown below (the fourth pin from the right on the top and the third pin from the right on the bottom).
• Everything else can be seen either on the video or in the attached photos. Most of the work is basic soldering and gluing. Good luck!