Eugen Barilyuk
Published: 15 February 2025
A flashlight is a useful thing to always have it on you. This ultra compact flashlight perfectly fits into this requirement as it is small and can be fitted to your keys. And it has an embedded USB-A connector, so you can charge the flashlight at any moment from any powerbank and wall charger. Here is the review of the flashlight and its disassembly.
The manufacturer claims the following specifications for this flashlight:
In a typical manner for marketplaces, you get half the truth in the specifications. The manufacturer data for battery, power and charging time is not correct.
The actual battery capacity is not 70 mAh but 55 mAh.
By the way, this flashlight is a fire hazard. The battery of this flashlight does not have any protection (BMS) and the flashlight does not have any li-ion charger. Scroll the article down to read more about the danger of this flashlight.
The claimed power is also incorrect if we analyze the components used in this flashlight. The value of the current limiting resistor shows the power of this flashlight should be 1,6 watts, which is insane for the tiny LED of the flashlight and would blow it instantly. But the current limiting resistor is useless as the flashlight's tiny battery can not produce the current this resistor is rated for. Basically, the power of the flashlight is limited by the battery's internal resistance.
Judging by the LED used in the flashlight, the real consumed power of the flashlight is approximately 0,1-0,2 watts. Which is way, way lower than 0,5 watts claimed by the manufacturer.
The flashlight has no visible switches to turn it on and off. Activation is done by rotating the LED lens. The lens has a bump that is clamped with the switch.
To charge the flashlight get the cap from the device rear end by rotating it slightly. The rotation frees latches on the cap from the lock and the flashlight falls off.
Next, simply connect the flashlight to any USB-A port available
The flashlight can not be disassembled reversibly. The white plastic part around USB is glued to the yellow case.
Nothing else except the glue holds the white plastic in the yellow case. The whole flashlight structural integrity depends on this thin strip of glue since the white plastic is the connection point of the cap, and the cap holds the flashlight on the keychain.
The front lens, on the contrary, can be easy and safely disconnected since it uses clips. Firmly grab the lens ring and give it a little bend as if you wanted to break the flashlight in half. The clips will come out, and you get access to the battery and the LED.
But the flashlight internal components can be removed out of the yellow case only through the back, so you need to break the glue that holds the whole flashlight as one useful piece.
That's a real mistery why the engineer who designed this flashlight did not add two clips for the white plastic element and yellow case to be connected by clips. Instead a glue was chosen, and that adds another manufacturing operation, which costs money.
One may argue that adding two clips to a press molds that produce these two plastic elements of the flashlight costs money or it is mechanically hard. That would be a good point if not the guide pin, which is useless and serves no practical purpose, but the designer still put efforts to create this guide pin and it was carved in the metal of the press moulds.
The schematics is rather straightforward and consists only of several components:
The flashlight has two distinct operational modes:
Normal flashlight operation of producing light is conducted with elements: Li-ion battery, switch SW1, resistor R2 and a main white LED.
When a user turns the flashlight lens a special bump on that lens pushes the switch SW1to close the circuit. The resistor R2 with the value of 10 Ohm limits the current rushing through the main LED. Without this resistor the current would be to large for the LED to handle, and the white LED would destroy itself. But the tiny battery of the flashlight simply can not produce enough current for the resistor R2 to step in action.
According to the Ohm's law, the 10 Ohm value of the resistor R2 at the voltage of the fully charged li-ion battery (4,2 volts) would produce the current 4,2/10=0,42 Amperes.
The main white LED of this flashlight is rated for the current of 0,1 Amperes. The current of 0,42 Amperes would instantly fry the white LED.
To get the real electrical power consumed by the white LED we need to use a multimiter in the milliamperemeter mode. The measurement established the white LED consumes 0,046 Amperes. The battery at the time of measurement was charged to 4,06 Volts. This gives the consumed power of 0,186 watts. Way less than claimed 0,5 watts by the manufacturer.
The components on the left part of the scematics are responsible for charging: USB-A connector, resistor R1, diod D1. For charging indication the red charging LED and its resistor R3 are used.
When a user plugs the flashlight intousb for charging the electricity starts flowing through current limiting resistor R1 (68 Ohm).
The USB typically outputs 5,3 Volts, however, Li-ion battery must not exceed 4,2 Volts. To lower the voltage the diod D1 is used. It is a silicon diod T4 with the forward voltage drop ranging from 0,715 volts to 1,25 volts according to its datasheet.
This means that if you are lucky and the diode D1 in your flashlight has voltage drop of 1,25 volts, the li-ion battery will be charged up to a maximum 4,05 volts. This means the battery will never overcharge and catch on fire.
However, there is almost a 100% probability your diode D1 has a voltage drop of 0,7 volts. This means your flashlight battery will be greatly overcharged up to 4,6 volts, skyrocketing chances of this battery to catch on fire.
Typically the li-ion battery should have a protective device (battery management system, or BMS) that shuts the battery at early stage of overcharging, reducing the risk of fire. The battery of this specific flashlught does not have BMS.
During the whole time the flashlight is plugged into USB, the red charhing light will glow. There is no mechanism for the red light to turn off when the battery is charged.
That is why never leave this flashlight unatended when charging it. To further increase safety do not charge the flashlight longer than 10 minutes.
The concept of a keychain flashlight with embedded USB connector is a genius idea. Too bad this flashlight is basically the only one existing in this category. All other so-called keychain flashlights are much larger and less convenient. And you also have to carry a USB cable to charge them.
What baffles most is that the genius idea of this flashlight was converted to real thing through lousy design approach. Engineer/designer could have easily made the flashlight even more convenient by designing the circuiut board morecompact. The flashlight could have been easily made at least twice thinner and a third shorter. While keeping the battery capacity.
Another major pitfall of this flashlight is the USB cover cap. It has a lousy lock that will someday unlock by itself. It requires only a small amout of force to unlock it, which leads to the flashlight becoming free from connection to the the keychain.
And to avoid the blast and fire in the pocket because the battery was overcharged, simply charge the flashlight for no more than 10 minutes. And definitely don't forget about the flashlight while its charging.