After easily converting an Ikea Dioder LED lamp to run off the 12V battery in my camper van I decided to make a return trip to Ikea to find a reading light to put above my bed. I didn't realize until I got home and opened the box that the Jansjo is a lower power item. It makes perfect sense since it has only 1 LED versus the many the Dioder has but I didn't consider that when I was looking for a lamp to convert for this project. Oh, well, just an opportunity to get hacking I guess!
Step 1: Tools
To complete this project I used:
1. Side cutting pliers, aka Dikes (DIagonal CutterS) or snips
2. Wire stripper
4. Razor (usefull for splitting two-wire electrical cable)
5. Soldering iron and solder
6. Multimeter (for verifying positive and negative. If you follow these instructions and photos you will not need this.)
The needle nose pliers were not used.
Step 2: USB Charger
Lucky for us the Jansjo power supply clearly states the DC output that is sent from the power supply to the lamp. It is listed as as 3 Watt lamp-- 0.75 Amps at 4 Volts (Power/Wattage = Current (Amps) x Voltage). There is circuitry in the head of the lamp that further adjusts the electricity running to the LED so I figured (correctly as it turn out) that if I could get the voltage closer to the desired 4V than the 12V off my battery then I could run the lamp without burning out the LED.
Guess what's close to our desired power... A USB car charger! I picked one up from the dollar store. 99 cents gets you a beautiful 1 amp at 5 volts. There was one screw to remove to take the whole things apart.
Photo courtesy of Erica Sadun- http://www.tuaw.com/editor/erica-sadun/
Step 3: Adapting the USB Charger
When you look at a typical car charger the metal point is the positive lead and the two bow-shaped peices of metal on the side are the negative lead. I soldered on an 18 gauge red wire to the positive input of the charger (obscured in the photos. It is the terminal that connected to the center point of the charger) that runs back to the positive terminal of my fuse block. I then soldered an 18 gauge black wire to the negative lead of the charger. Why 18 gauge wire? Mostly because I had some sitting around but also because it is rated to handle 2.3 amps max for power transmission; more than adequate. 21 gauge wire is rated for 1.2 amps of power transmission, I wouldn't suggest going with any wire smaller than 21 gauge.
Please note: the USB charger contains a small fuse. I removed it because I am connecting the USB to a 1 amp fuse located in my fuse block. If you are connecting it to the battery in a different manner you migh consider using an in-line fuse or something similar.
Face the charger with the plastic piece towards the top (as shown in the photos) . There are four metal terminals. The two in the middle are for data, the remaining two are for power. The left power terminal is positive, the right is negative. I pushed each wire through the small hole in the back of the plastic and soldered it to it's respective terminal.
Step 4: Modify the Jansjo
Cut off the connector that plugs into the Jansjo's power supply. Take a look at the wire that runs back from the switch to the power supply. One was writing on it, the other has a black stripe. The wire with the black stripe is the positive. Connect it to the positive output (red wire) of the USB charger. Connect the wire with the writing on it to the negative (black) wire coming from the USB charger. Insulate any exposed wire with electrical tape. Your Jansjo is now ready to be powered from your 12V power supply!
Diagram courtesy of cheaprvliving.com