UltraViolet Led Flashlight (Li-ion)

Hello!,

In this time, im going to show you how to make a portable UltraViolet flashlight. Also known as black light, It has the ability to reveal susbtances and other stuff otherwise invisible to the human eye. It has many funtional uses, for example to detect blood presence with the help of some chemistry or sterilisation and disinfection. For example; some substances are able to absorb the energy in UV light and immediately convert it into visible light. This effect is called fluorescence. The ink in highlighter pens contains a fluorescent dye that enables the ink to reflect vividly in sunlight and to glow strongly in the dark when a UV lamp is shone on it.

For this build you will need a few inexpensive parts. Starting with the power supply, which is given by two 18650s. Then we need a circuit to charge them up TP4005 with built in protection circutry. Next we will need a booster module to power our 3w.UV Leds. Also, getting some extra heatsinks for the leds is highly recommended. To turn the flashlight on and off, a switch will be needed.

The leds ,despite having a high efficiency ratio, they get very hot on their own, almost impossible to touch them more than a second. To expand the Led life time and avoid heat issues, It is must to add some kind of heatsink. Here the leds are soldered to an aluminum base plate heatsink, but it is a good idea to even improve the thermal dissipation. To do this, an aluminum plate is attached right behind the leds with M3 bolts and nuts. Don't forget to apply thermal paste too.

After having wired up the 3 Leds in series, power them with 10.8v. to make sure they light up. Note that your leds may have a different voltage rating so you will need to adjust the voltage to yours. Mines require 3.6v each so 3 * 3.6v makes the 10.8v.

For this step you will need at least one Li-ion cell (an 18650s) to serve as a power supply for the leds. If you want the light to last longer, you will need to add more capacity by adding more cells connected in parallel. In my case I used 2 cells, meaning a 1s2p battery. To correctly charge them up without risk, use a TP4056 (or anything compatible) with built-in protection circuit to ensure they dont drain too much. Please be very careful when working with Lithium based cells, they are very dangerous when mistreated. Also when soldering to their terminals, sand down them a little bit before applying the solder. Connect the positive lead to B+ and the negative to B- accordingly.

Once you are done, conect it to a usb charger. A red/blue led should light up showing the charging status.

We will need to hold all the electronics and the battery together, so get some some wood, lay the battery and the circuits and then cut the wood to size. Hotglue the battery firmgly to the bottom and side panel. Next you can place the charging circuit and hotglue it in place too. Also don't forget to add the Led panel in the front.

Start by making sure the battery is fully charged (A blue led should light up) and connect the booster module inputs to the charging circuit output taking care of the polarity. Once it is done, adjust the voltage out from the booster module to around 10.1v to 10.5v. Finally solder the leds to the outputs of the booster module. The leds should light up and not generate too much heat. Finish by hotglueing the booster module.

Well I guess this step is almost self explainatory. Just mount a switch in the side of the enclosure (The one that is closer to the circuitry). Connect the OUT+ (or OUT-, doesnt really matter) of the charging module to the Input+ of the boost module accordingly. Glue the the sidepanel to the enclosure once you know it works. Apply some hotglue to the conection if you want to avoid shorts, etc...

We are almost finished. What is left here is to glue together the top piece and the back piece (the one where the charging port is) and wait till it dries. You can also use hot glue here. Then we can proceed to sand down the edges and make them smooth.

Final touch, this will highly depend on your likes, etc,... In case, I went with some glossy EVA rubber glued with some woodglue (I know it is not wood, but it also sticks!) and cut the excess edges with a very clean and sharp knife.

In the end, we have a good portable UV light for a reasonable good price (less than 10€).

I dont think you will need any improvements in the future as 9w are outstanding without compromissing portability. However, you may want more runtime, in that case, upgrading the battery is the only thing possible. Mine lasts more than an hour, so its more than enough to have fun during the night. Finally this is a good project for those who like strange colours leds and anyone who likes to explore about UV.

This good fun, explore, explore, explore, that's what science is,
exploration, finding out new things, so have a good time with it"

- Charles Townes