A while back we covered the nifty Sunnan solar powered desk lamp from IKEA, highlighting its usefulness while making note of some of the things we would like to change. In that list of possible improvements we mentioned increasing the both the battery capacity and the solar power generated. This modification of the Sunnan lamp does both of these and more! Thanks to our friends at Adafruit, we were able to find a solution for re-wiring the lamp to provide a USB charging port for boosting the charge of small portable electronics. (If you want a fully functioning, high-powered system, have a look at our Spark iPad solar charger) So for this modification we will show you how to:
1. Replace the stock batteries with higher capacity batteries
2. Modify the battery compartment to accept Voltaic Systems small solar panels
3. Re-wire the lamp to accommodate Adafruit’s MintyBoost module
Disclaimer: We here at Voltaic Systems are trained professionals and have taken precautions to ensure that this modification is fully functional; however, we cannot guarantee that it complies with any safety standards or regulations and is not responsible for any damage that might occur to the lamp, batteries, or any other device connected to the modified circuits. Batteries can overheat and catch fire if overcharged or short circuited. Attempt this modification at your own risk!
- Things you’ll need:
- Sunnan IKEA Lamp (available here)
- soldering iron, solder, solder wick/pump
- pliers, wire cutters, wire strippers, utility knife
- phillips head screwdrivers (medium and small)
- rotary tool (dremel, etc.), cutting wheel, routing bit
- epoxy putty (quick setting is the best, we use JB Weld)
- power drill, 5/16” bit
- MintyBoost v3 by Adafruit (available here)
- 2x Schottky Barrier Diodes (1N5817)
- 1x 39K Ohm resistor
- Small piece of circuit prototyping or perf-board
- USB output wire from Voltaic Systems
- 2 Watt solar panel from Voltaic Systems
UPGRADE THE BATTERIES
Remove the Battery Pack from the lamp base and remove the four screws from the corners.
Remove stock IKEA AA NiMH batteries. Replace with higher capacity cells. We used Tenergy 2700mAh cells. Energizer, Duracell, and other provide comparable high-capacity cells. This boosts capacity of the battery pack from about 4.3Wh (1.2V * 1.2Ah * 3 cells) to about 9.7Wh (1.2V * 2.7Ah * 3 cells).
INSTALL INPUT FOR MORE SOLAR PANELS
Remove the screws holding the circuit board inside the battery pack in place. This board contains a fuse, blocking diode between the solar panels and the batteries, and a current regulator to limit the amount of current flowing from the batteries into the light. De-solder the wires connected to the circuit board. Set this board aside, as we will be re-installing it in the lamp base a bit later.
Our External Solar input will be made from the Voltaic Systems USB output wire (available at the bottom of this page). Cut the 3.5×1.1mm female end of the USB output wire from Voltaic Systems about an inch into the curly wire. Strip back the jacket to gain access to the two wires. Strip and tin the tips of each of the wires.
Drill a 5/16” hole in the side of the battery case to permit access the 3.5×1.1mm External Solar socket
Insert the 3.5×1.1mm External Solar socket into the battery case and epoxy it into position.
While the epoxy is setting, create a diode junction using the two 1N5817. Connect the cathodes together and leave the anodes open for connections from the solar panel and the external solar input. This allows energy to flow from both the supplied Sunnan Solar Panel and the External Solar input into the batteries without them interfering with one another, and prevents the batteries from discharging into either panel.
Solder the solar panel + and the external solar + wires, one to each of the Anodes on the diode board. Solder the battery + and the connector + wires to the Cathodes on the diode board.
Join all of the negative wires in the battery pack and solder them together (battery -, solar panel -, and external solar -. Then solder them to the negative tab on the battery pack connector socket.
Check your wiring and make sure that there is a positive voltage (around 4V if batteries are fully charged) between the connectors for the battery pack socket. Then close the battery case.
MINTYBOOST!
Assemble your Adafruit MintyBoost v3. The only change you need to make is to replace resistor R4 with a 39k ohm resistor. Instead of connecting to the battery pack provided with your Minty Boost kit, attach about 6 inches of 24 AWG stranded wire to the + and – points on the PCB.
The replacement of R4 with the 39K ohm resistor reconfigures the MintyBoost USB pin voltages to measure as below:
- Pin1 = 5V
- Pin2 = 2.75V
- Pin3= 2V
- Pin4 = 0V (ground)
This tells Apple devices, such as the iPad2, that is can draw up to 1A from the supply. If you wish to limit the current to 500mA, use the resistors supplied with the kit as directed. Please note that the iPad2 requires the 1A configuration to charge and that by reverting to 500mA, the iPad2 will not support charging.
REWIRING THE LAMP
Turn the lamp base over and remove the 4 screws.
Remove one of the cast-iron weights in the base of the lamp.
Using a routing or grinding bit, remove the screw-post to create a space for the MintyBoost.
Mark and route a hole for the USB port of the MintyBoost.
Peel off one side of the small adhesive pad included in your MintyBoost kit and place the pad in the lamp base.
Remove peel off the other side of the adhesive pad and insert the MintyBoost.
Remove the two screws holding the cover for the two-prong connection to the battery pack in place.
Mark the prongs indicating which wire was soldered to them (black is negative and white is positive). Remove the wires from the solder pads.
Solder the black wire going to the LED to the “L-” pad on the Sunnan circuit board, and the white wire running to the lamp switch to the “L+” pad on the Sunnan circuit board.
Solder a wire from the negative prong to the “BT-” pad on the Sunnan circuit board, and solder a wire from the positive prong to the “BT+” pad on the Sunnan circuit board.
Use a cutting wheel or routing bit to remove enough plastic to stow the Sunnan circuit board at the base of the goose neck connection.
Remove the fuse on the Sunnan circuit board and replace with a piece of jumper wire.
Solder the negative power wire for the MintyBoost to the “Sun -” pad on the Sunnan circuit board. Solder the positive wire for the MintyBoost to the “BT+” pad on the Sunnan circuit board.
Tuck the Sunnan PCB into the pocket you routed out near the goose neck in the lamp base. Tidy up any wires from the minty boost. Then close everything up! You’re done!
Connect an external solar power to the battery pack and place in sunlight to charge.
After a day of charge, you should be able to use the desk lamp as normal AND give your iPad a boost.
We’re still doing testing, but the results so far are promising. Here’s a look at the type of performance you can anticipate from these modifications:
With a 1.4W panel attached to the .5W panel of the Sunnan lamp, we can generate a peak of 1.9W. Under normal real-world conditions we can expect to produce about 1.5W average. NiMH batteries are only about 65% efficient at storing that power so we can expect that a 9.7Wh capacity battery pack like the one we’ve modified the Sunnan with will take roughly 10 hours to fully charge (9.7Wh / 1.5W / .65). Assuming that the charge transfer efficiency from the NiMH batteries via the MintyBoost into the iPad2 is roughly 70%, we can expect about a 25% boost to the iPad2′s 25Wh battery from a full charge (9.7Wh * 0.7 / 25Wh).
As far as the lamp run-time is concerned, the internal current to the LED is limited to 200mA. Assuming that the average battery pack voltage is 3.6V (1.2V * 3), we can estimate the power consumption of the LED at about 720mW (3.6V * 0.2A). From a 9.7Wh battery, we get just over 13 hours of light from a full charge (9.7Wh / 0.72W).
Notes: Discharging into an iPad 2 causes the battery pack to become warm. Although it is possible to both use the lamp feature and the charging port, it is more effective to use only one at a time.