Modification of a flashlight (from AAA batteries to 18650 battery)

Selecting and purchasing a flashlight is a difficult and tedious task. At least for me. I approach this matter with all meticulousness and responsibility. It is necessary to take into account all the advantages and disadvantages of the product. Type and capacity of batteries, parameters, weight, degree of water resistance and much more. So that he does not fail at the most inopportune moment. I wanted to buy a small pocket flashlight, waterproof, powered by a single 18650 battery. However, I could not find the desired product in local stores. I was already thinking about ordering from an online store and, after waiting 2-4 weeks, getting what I needed... But suddenly I came across something that almost suited me. Almost. The flashlight had the dimensions I needed and all the necessary qualities, but there was one “but” - it worked on three AAA batteries (pinky).


Having a special container with four constantly charged 18650 batteries in my backpack, I absolutely do not want to use other batteries. Moreover, such small and not capacious ones as little ones.But there is always a way out! Having examined this flashlight in the store, a modification scheme immediately emerged, and without thinking twice, I purchased it with the goal of remaking it in my own way in the near future.

Will need

• A burr machine with a cutting disc (or an emery machine).
  
• Soldering iron, tin and flux.
  
• Plastic tube (for housing insert).
  
• Aluminum self-adhesive foil.
  
• Scissors.
  
• Stationery knife.
  
• File.
  
• Sandpaper (or sanding cloth).
  
• Secondary glue.

Flashlight conversion

The main problem is that the flashlight’s “native” power supply (the housing in which three AAA batteries are located) is slightly wider, and one and a half centimeters lower than the 18650 battery.

This means that the body of the flashlight itself will be too small in height for 18650. In terms of voltage, 18650 is almost identical to three little finger batteries, 18650 produces 3.7 volts, and three little finger batteries give a total of 3.6 volts (1.2 × 3 = 3.6) . This means that if the body is too small, you need to lengthen it. It was quite problematic to find a suitable insert tube that would fill the extra space between the battery and the walls of the flashlight. In the end, I was never able to get a suitable insert... I simply took a more or less suitable tube that included 18650 and, installing it on a drill, removed the excess thickness from the rotating workpiece from the outside with coarse sandpaper! So, let's disassemble the flashlight. Unscrew the front and back parts of the flashlight from the middle one and set it aside. Using a burr with a cutting disc, we cut the middle part of the flashlight body into two equal halves.

We sand the sawn edges with sandpaper so that they become even and smooth.

Next, we insert the liner tube into the front part of the flashlight with a reflector screwed onto it, and put the back part on top with the bottom and button screwed onto it. The result is a new, elongated body that fits the width of 18650.


Now let's adjust the height, insert the battery into the case, measure out the excess on top, take out the liner and cut off the measured edge with a utility knife.



Also in the design of the flashlight, inside the body, there are two metal rings and a metal strip that connect the plus and minus on the switch button. Naturally, after lengthening the body, the metal strip became too short for the new design. We also had to adjust the rings to fit the liner tube.

The layer of soft plastic was quite easily and quickly removed with a file from the edges of the liner, where the ring should sit.


The second, front ring, was inserted inside the front of the flashlight, where the reflector, lens and Light-emitting diode, so I didn’t have to mess with it. Let's do it simpler with the metal strip connecting the rings; Simply stick a strip of self-adhesive aluminum foil onto the liner.

We put the back ring on the prepared back part of the liner.

Now let's work on the “head” of the flashlight. On the former power supply, with pinky batteries, there was a small bulge on the positive contact that was in contact with the positive. On the 18650 battery, both contacts are flat, so I had to solder the same spring to the positive contact of the front part of the flashlight as is on the negative, rear part.


Now let's put the new body together.

All the details fell into place like family! All that remains is to drip super glue into the joints between the liner and the sawn edges of the body to restore the tightness.There is still space left, or rather, it turned out to be a groove that was formed after installing the sawn ends of the old case on the liner. This is an individual matter for everyone; Before gluing all the parts, you can fit a piece of tube with suitable parameters to this place. I decided to just wrap a little tape and black insulating tape there; Might be needed somewhere.

Thus, we “transferred” this device from three batteries to one, equal in voltage, thereby saving ourselves from the tedious charging of the power supply with small and low-capacity batteries.

The above changes did not in any way affect the quality of the flashlight (brightness and water resistance). Except that it has become one and a half centimeters longer.

Watch the video