Cheapest? Keychain flashlight Mod

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DoubleA
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Cheapest? Keychain flashlight Mod

I’ve always had a craving for colorful glowy lights, probably after I saw this scene in that movie Love
Ever since then I was on a quest to find, accumulate or create any and every colorful glowy illuminating things I could ever come across or even imagine.

So this is my latest mod project, It’s simple. Sorry I did not post all my other glowy things since there are too many and it would take forever to get them into this forum, but I can assure you that won’t stop me from trying..

I came across this keychain light in Aliexpress (Goes by the name Cheapest led flashlight or something) when I was looking for a Glotoob clone. It costed about 0.5$ each including batteries but if you buy a 10 pack you could get all of them for 1.5$ or so. Since I obviously didn’t want 10 of them I decided to buy just 2 even if they costed more. There are a lot of different sellers selling the same thing or slight variations of this in different names and prices. They had multiple shell color options and also offered colored LEDs but all of that were clear LEDs so they threw all that light into the front instead of flooding the entire room like a glow stick.So I decided to buy a couple of them and mod it myself. Crazy

Basically it operates like an LED throwie except that it uses 2 CR2016s instead of a single CR2032. This has an advantage which is the LED is getting 6V so it shines much brighter than it should , but this also has disadvantages mainly the LED is overdriven and also the capacity of a CR2016 is much lower so expect much lower runtime than a CR2032 throwie. The lifetime of the LED will also be affected but since these LED’s are too damn cheap who cares if they won’t last a year? These lights If I’m correct were meant to be use and dispose which is why they chose overdriving them, to get maximum brightness. When the battery died people usually buy a whole new unit instead of trying to replace the batteries or LED.

Here are the pictures. The first one is the advertisement pic from Ali showing all the different Color options. They also have a UV LED variant which is very useful to check for fake currency notes on the go. I chose the ‘Clear’ one, although I may buy other colors later(I have my eyes set on you Purple). Pictures show metallic screws but I got black screws, doesn’t match with a clear shell .

This is one below the actual photo of what I got. Both sides are shown here. Open pictures in new tabs to see higher resolution

The build is fair enough. The plastic edges are decent, but not perfect. there are areas where the seams are not cut properly but not such a deal breaker. The feel is matte finish which I like nice and grippy to hold. I believe it can take a little bit of punishment and still manage to stay alive. Minor drops seems to do no damage at all since it’s extremely light weight. Key ring is generic but can be the attached to a lanyard or a carabiner or dog tag. Handy.


The top side has a slider which pushes the cathode of the LED to make contact with the battery and the slider stays in place so the light stays on until the slider is pushed back. There is also a momentary ON function, the top side (the side where the slider is) is flexible you can squish/press the top and the LED cathode will touch the battery until you let go.It’s a useful function if you want to momentarily activate the light or make a morse code signal or something.


Side view of the slider switch to illustrate better. Also a better view of the seams.

Now the teardown

It’s extremely easy to disassemble and mod. Just unscrew the 4 tiny screws and the whole unit comes apart. Just don’t forget to remember the battery polarity position. The slider has a slot to hold in place the cathode. The top section also has a slot for the cap rim of the 5mm LED. That slot will NOT accept 5mm straw hat LEDs as their rim is slightly wider and will not fit into that slot. The interior has just enough space for the LED leads and the battery, no space for resistors (didn’t try smd resistor)

Now the mod

First of all I decided to replace the CR2016 batteries for mainly 2 reasons. First it being cheap Chinese variant with low capacities and Second being it provides too much voltage and current than LED needs. Also CR2032s are much easier to find in shops as they are popular for being CMOS battery.
In case you didn’t know a CR2032 has the same height as 2x CR2016 combined, like the picture shows.
2016 stands for 20mm width/diameter, 1.6mm height. So do the math for 2032 and you’ll get the idea. Big Smile
I used Varta CR2032 batteries because there seems to be no clones for that yet since it’s not very popular. Every other brand like Maxell,Sony,Panasonic etc have their exact clones flooding the market with less than 50% advertised capacity. CR2032’s have a lower voltage than the LEDs requires (except RED) so the LED will be underdriven + the battery has a higher capacity than 2x CR2016s combined. This means ultimately longer runtime with lower than usual brightness.


Now for the LED part. I used a 5mm Emerald green LED diffused/frosted with 20mA rating to replace this unkown clear white LED. I just had to trim the leads with a nipper and bend the Anode a bit like the default LED. It fits perfectly into the slot.
Tip —> If you don’t have a diffused/frosted LED you can just sand it’s surface with a sand paper or scotch brite dish washing pad and it will be diffused.
Now place the new CR2032 battery (remember the polarity, both for the LED and the battery). Cathode side faces the switch/squishy underbelly. Close the 2 shells and screw it and your done. Thumbs Up

Shown below is the mod and the default one placed side by side.

I intend to use this in emergency situations like a disaster or something (zombie apocalypse maybe Sick ). It will light up for sure because of the reason that it uses bare minimum/ least components. No circuitry to go wrong, will tolerate splashes etc, lithium coin cells have good shelf life.So it’s definitely going into my survival kit whereas the unmodded default white one I will use as EDC carry in keychain. Useful for looking inside a bag or finding keyhole of door.

The default white LED glows very bright due to it being overdriven. The throw of the white is pretty good. For comparison it shines as bright as a cell phone LED flash used as a flashlight but this one has decent reach because of the narrow angle of the 5mm LED as opposed to cell phone floody smd LED. I would say indoors it can illuminate up to 3 meters max, outdoors maybe 1-2 meters.

The Green LED does not shine at it’s fullest due to it being underdriven by a lower voltage and current. It has the same brightness as any Green LED throwie. More than enough for visibility inside a pitch black dark room ( you know like being trapped inside a sewer underneath a secret Soviet army base in Afhganistan Big Smile ).
Outdoors the green light is pretty useless for illumination. You can see what’s in your hand, like a map or something and also anything with 2 feet close to you but keep in mind that I did not make this for outdoor navigation or trekking. It’s sole purpose is to provide emergency light when you have none. So basically it’s like a backup light when your lantern or flashlight dies. Additionally you can use this to signal someone who is far away, but not too far away. I would say 25 -35 meters away, Green light has the maximum luminous intensity of all the colors so it has the maximum visibility from distance due to it’s wavelength characteristics. Use clear non frosted LEDs if you want to increase this signalling distance, a clear green 5mm LED can be visible up to 100 meters away depending on the environmental condition. If it’s a foggy environment then a Red light will penetrate the fog much better than any other color.

Fortunately the Green LED I had was not 100% diffused, it had a bit more throw towards the front than to all other sides, so you can use this to your advantage for signalling or pointing at maps.

Some thoughts.
White Default—>Good enough to be used as a indoors only flashlight, or inside of a car. Outside it can be used for find door keyhole etc. Also works as a backup light.
Green mod —>It serves it’s purpose as a backup emergency light. Provides prolonged illumination runtime for emergency situation. I believe it to be well above 50 hours.

I’m planning to use other colors as well, but Red will not be practical due to it’s low forward voltage it will draw more current and runtime will be shorter. If I can manage to solder an smd resistor to Red lead then it would be great.
I also plan to get Cyan glow by combining the Green+Blue leads of a tricolor RGB common cathode 5mm frosted LED since I couldn’t find any 5mm cyan LED out there.

So that’s it for now. I will update the post with current draw measurement. Let me see if I can get the beam shot of the White default LED with my crappy camera.

Do let me know your thoughts in the comments section. Smile

Update:-Current measurements

2x CR2016 Open Circuit voltage – 5.9V

White – starting 52mA – 26mA and dropping after 2 minutes
Green – starting 76mA – 28mA and dropping after 2 minutes

1x CR2016 Open Circuit voltage – 2.9V

White – starting 3.7mA – 3.4mA and somwhat steady after 2 minutes
Green – starting 4.2mA – 4.1mA and somwhat steady after 2 minutes

1x CR2032 Open Circuit voltage – 2.9V

White – starting 14mA – 8.1mA and dropping after 2 minutes
Green – starting 7mA – 6.5mA and dropping after 2 minutes

At 5.9V green is so bright that it doesn’t look like green at all.
It looked More like a bit of green tint in a somewhat white LED

Current output is improved due to the series setup of CR2016 batteries
Coin cells can provide a good burst current but shortly after the max continous discharge
limitation kicks in.

I would highly recommend using 3V for color LEDs since but White looks OK to the eye when overdriven.

and on the first day he said "Let there be light"...

Edited by: DoubleA on 11/13/2017 - 11:55
Suncoaster
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Cool ideas.
I’ve always tossed fauxtons after they run down, now I’ll have to try a CR2032
and coloured LED !

"In the land of the blond the one eyed man is king."

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DoubleA
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You could also use a LIR2032, which is a 3.6V rechargeable variant of the CR2032 with a less than a quarter of the capacity, but is re-usable.

and on the first day he said "Let there be light"...

snakebite
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i did a few with ebay hi cri and lir2032.
for the intermittent usage pattern they do fine with the reduced capacity.
this comes under the heading of making a silk purse from a sows ear.

DoubleA
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Well said.

I have updated my post with current readings.

and on the first day he said "Let there be light"...