Sunday, 12 June 2011

Ikea SUNNAN lamp

Last week I went to IKEA to grab some more storage containers for my lab (I can't see the bench at the moment for all of the junk - overhaul and blog posts coming as soon as I clean it!) and as usual I found myself staring at all of the glowing stuff in the lighting section! Their LED lighting section is becoming quite substantial. LEDs are great and I love building things with them but the mechanics of fitting them professionally into an enclosure often frustrates me - perhaps these lamps would be easier to upgrade rather than to retrofit a non-LED lamp.

Anyway, storage containers was my mission but I did grab a small souvenir - a SUNNAN lamp.

(Image from IKEA)

This little lamp is a solar powered and runs a small PCB with 3x chip LEDs, it has spherical optic which provides a reasonably wide and even beam. The interesting part of its design is that the solar panel is built on top of a removable battery box - you pop it out and put it in the sun rather than moving the whole lamp (which really isn't big or heavy).

After leaving the SUNNAN burning for a couple of hours I was surprised by how well it was lasting on its first charge - the white LEDs where getting dimmer but still quite usable. As white LEDs usually have at least a 3v Vf (forward voltage) and the battery pack stated 3x NiMH cells (~2-3.6v cycle dependant) I was curious to know what else was in the lamp. How was it driving these LEDs for so long? Did it have a small boost converter IC or something like a Joule Thief to help extract as much power as possible? How do they mount the LEDs? How do they make it for ~$19? How does the optic work on my other LEDs (especially my 100W LED array.....)? Too many questions - only one thing to do:

(Image from Wikipedia)

First stop - the bottom housing... Nothing. Switch, wires, contacts for battery pack.

Next - the battery pack... A little bit more rewarding, 3x NiMH AA cells, a small PCB with a blocking diode to stop leakage through the solar cells and a glass fuse with axial PCB mount caps. I guess the fuse is to stop the batteries getting hot if you decide to get adventurous and stick a paper clip in the battery pack terminals... Still disappointed.

A bit of prising and I was in the lamp head:
Optic mount & screwdriver marks (top right)
Three more screws to go and we're there:

Lamp head PCB

A constant current driver, filter cap and 3x resistors - not as interesting as I was hoping for. I guess the LEDs must have a pretty low voltage drop for this to be useful, didn't have my meter in hand so I didn't measure them.

Bonus image: Close up of an LED which shows flux splatter, a couple of rogue solder balls (or probably also just splatter) and some emission from the LED, which appears to be two small LEDs joined in one package!

Close-up of an emitter

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