Upgrade Solar Keychain Flashlight with Supercapacitor

There are several online and retail stores where is available a kind of small LED flashlights, they are rechargeable by solar energy. There are reports of prices around 1 USD/EUR/GBP depending on the country. However, all aren’t good news, some bloggers reported that many aren’t rechargeable at all, because they were equipped with disposable CR2016 batteries, or with damaged solar panels, unsoldered or simply fake solar panels.

The most common fail of this type of flashlight is battery undercharge (usually when stored for long periods in dark places like pockets or drawers) . This damage isn't reversible, but the case, push button and the solar panel could be reused to make a "more durable" solar flashlight

Step 1: OPEN THE CASE AND GRAB THE USEFUL THINGS

COMPONENTS

• Damaged solar keychain flashlight but with real and good condition solar panel.
• 5.5V 1F for bigger supercapacitor that fits inside flashlight case
• Red led
• Schottky diode
• 5.1 Zener diode or two green and one red LEDs
• 220 ohm resistor

With the help of a spudger or a pry tool open the case and desolder the solar panel and push button.

Step 2: MAKE SOME SPACE FOR SUPERCAP

• Cut super capacitor terminals, as much as possible, but leaving some space to solder a thin wire
• Scrap some plastic from the case, to give more room for the super capacitor.

Step 3: BUILD THE PCB

Bake your favorite flavor of PCB (Etched, universal, Manhattan, ratnest). Be careful placing the push button and the Red led, because the case could't be closed or the button pressed!

Two versions of the circuit are provided, use whatever you like

Step 4: SOLDER, ISOLATE, CLOSE & CHARGE

Solder the supercapacitor and solar panel to the PCB with very thin enameled wire. Put some kapton tape to avoid short circuits between metallic exposed parts.

Close the case and charge for at least a day near a window.