Enhanced Ljusa Charger



Introduction: Enhanced Ljusa Charger

This is my first instructable, so bear with me.

With a few basic items you can build a hand-crank powered emergency cell phone charger, very useful if and when the power goes out, and it's not dependent on any batteries.


  • IKEA LJUSA flashlight($5 at IKEA)
  • USB car charger($1 at Dollar Tree)
  • Soldering iron and solder
  • Double-sided tape
  • Wire strippers
  • Hookup wire
  • Phillips and flat-head screwdrivers

How it works:

The Ljusa uses a hand crank connected to a gear reduction drive that powers a small brushless motor, which acts as a generator. The power from the generator is passed through a network of diodes wired as a full-wave rectifier, which insures the correct polarity DC voltage is supplied, regardless of which direction the crank is turned. The rectifier in turn charges a 1000uF capacitor, which in the original design powers the LED's. This project re-purposes this setup to power a 12V USB car charger.

Most USB car chargers are based on a simple "low drop-out" switch-mode step-down regulator chip. Though "nominally" designed for the 12-15 volt input from your car's cigar lighter, they will operate on as little as 6.5 or 7 volt input. Cranking the Ljusa for 30 seconds or so charges the capacitor to about 7 volts. Even higher voltage is possible if you crank the thing continuously, with the net result that the flash-light can power the charger.


I got some ideas for the implementation from hudasx's Ljusa-themed Instructable:


Also, this great page on using a Ljusa to power a kid's toy provided much inspiration:


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Step 1: Disassemble the Flashlight

You need to remove the lamp assembly from the Ljusa to access the wiring within. Turn the flash-light off. The lamp assembly is attached to the flash-light by a push and turn locking mechanism. You can see one of the latches in the above picture. You should be able to remove the lamp by turning it counter-clockwise, but it is very snugly attached. It is also possible to pry it off using a flat-blade screwdriver.

Once the light assembly is off the flash-light, you'll see it is connected by two wires. The black wire is negative and the white wire is positive. Carefully unsolder these wires at the light assembly.

Step 2: Disassemble the Car Charger

Next you need to disassemble the car charger to obtain the printed circuit board within. The exact steps to disassemble the car charger will vary based on its design. Typically, there's a plastic collar around the positive terminal that can be unscrewed and removed. From there it should be a simple matter of unsnapping the two halves of the case apart. As you disassemble, note where the positive and negative terminals of the charger connect to the circuit board. Note that the design may rely on contact between the terminals and the board; the connections may not be soldered.

Step 3: Solder the Lamp and Car Charger Together

Strip the ends of the wires coming out of the flash-light. Solder the black and white wires to the negative and positive terminals on the USB charger board. In the photos above, I had broken the white wire coming out of the flash-light, and soldered in a new orange hookup wire in its place.

Once you've soldered the connections, crank the Ljusa for a few seconds and turn on the switch. If the pilot light on the charger turns on, plug in a USB device to test charging.

Step 4: Attach the Charger Inside the Ljusa

Once you've done a basic check to establish the charger is working, attach the charger board inside the Ljusa body using double-sided 3M tape, or hot glue. Keep it in a safe place and it will be ready to charge your phone during the next power outage. Note that, depending on the device's current draw, you will likely have to turn the crank continuously to keep the charger powered up.

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