I’ve had my IKEA Sunnan since summer 2010. I put it into bright sunlight all the time. The only way I can make it light up full-blast is to dismantle it, charge the batteries externally and reassemble it again.
What is wrong with it?
When I disassembled it today I immediately measured the individual battery voltages, suffice to say they were pretty empty. One of them was near zero, the remaining 2 close to 1V. The batteries are currently in ‘hospital’ undergoing a sequence of charge-discharge cycles in my battery charger. No errors so far and the last time I checked, the battery capacity was close to the spec’d 1200mAh. I shall know tomorrow what the ‘doctor’s’ final verdict about them will be.
Holding the lamp close to a light source makes the LEDs light up, therefore I conclude the solar cell is still in good shape. It delivers about 5.8V in bright light.
The pretty unsuspicious top side, just a bunch of wires and a small glass fuse – not HRC certified I presume. And not accessible from the outside. If this were a multimeter, it wouldn’t get an “eevblog thumbs up” I guess.
The bottom side reveals a Schottky diode (0.22V) and a A705N constant current LED driver. There’s room for a smoothing capacitor, but it’s missing. Seems like they had to save a couple of cents.
The schematic with all the components placed. The solar cell is just paralleled with the 3x 1.2V batteries, with the Schottky diode preventing reverse current through the cell.
I was suspecting the LED driver might be sucking the batteries dry, so I measured it’s quiescent current to be sure. The datasheet claimed 200µA. At high voltages the QC saturates at about 120µA (good). At lower voltages it drops rapidly, which should be good for the batteries.
The forward voltage of the LED (measured with my DMM to be about 2.42V) is quite a good match for 3 very empty NiMH cells. The energy is used up pretty well.
It’s not the solar cell and it’s not the circuitry. Currently it seems that either there’s one dead / weak cell in there and / or self discharge rate is way bigger than what is replenished by light exposure. Even putting the cell next to a pretty bright light bulb doesn’t seem to keep the batteries in good shape… The cell’s voltage should be high enough.
Maybe I should add an external charging port, but I just don’t feel like it. Such a nice and bright LED + lens and it has to come with such a “mentally challenged” battery management.