IKEA Sunnan – revisited

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.

4572383202_bf794f135c_o

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.

5321263958_d67057b1a3_o

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.

5321262644_c5ee5d3056_o

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.

5320658055_98abee7af3_o

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.

5320657925_60ae6bb95b_o

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.

Shucks!

This entry was posted in Electronics. and tagged , , , , , , , . Bookmark the permalink.

19 Responses to IKEA Sunnan – revisited

  1. Karen says:

    There’s a real physical switch in between the batteries and the LED circuit, right?

    Have you tried putting in fully charged batteries and seeing if there is current leakage through the solar cells?

    NiMH charging ICs aren’t that expensive (albeit overkill)….

  2. robert says:

    Unless the Schottky diode is a fake there shouldn’t be any sizable leakage going that way. Probably the self discharge rate of the batteries is dominant here. Now I’m keeping the battery pack close to my desktop lamp. That should compensate for that.

    But at least a plug for an external charger sounds compelling.

  3. Rino says:

    Hi, i want to hack this lamp to be connected to a power adapter. Do you know how to connect it to the lamp?
    Thanks!

  4. robert says:

    For charging?

    If the batteries are removed, you can just connect external power to the pads of the missing C1. Correct polarity required.

  5. Rino says:

    Ok thanks! I will try this!
    Bye

  6. Neganur says:

    why would you need an HRC fuse in this device anyway.

  7. robert says:

    Good point. They’re much nicer to look at, more ‘manly’.

  8. JC Silva says:

    Hi,
    I designed a Solar Powered LED lamp some time ago (before those Swedes thought about it). I designed my switching converter for the LED and went with the same Schottky solution to the charger. If look around “every-google-one” uses it…
    And it is lousy!!! I repent not having designed a controlled charger! it is bad, bad, bad… kills NiCds after a year and NiMH after much less than that.
    The repetitive incomplete charging cycles, the deep discharges and the unusually high discharge current (at least in my case) kills the batteries.
    The reality is that you’d need a much bigger solar panel, if the solar panel efficiency is about 10% (the ones in laboratory) for every minute of full power sunlight you’ll get 6 seconds.

  9. robert says:

    Adding a proper charger IC would probably have added 50¢ or thereabouts. I guesstimate that with the right kind of battery they can make it just last long enough. It’ll go bad 2 days after the warranty has expired.

  10. WikiaLink says:

    Maybe the fuse is required in any country in the world?

  11. Ilija says:

    Dear sir,

    I would like to add a IC charger to this IKEA light, so how much V and A the charger must have or how to connect it to light? Thanks for your answer!

  12. robert says:

    You need a 3-cell (3.6V) NiMH charger, which is the preferred way. Connection is right across the battery pack (“+” to “+” and “-” to “-“). You may find something on ebay.

    As an alternative you could also build a ‘constant current’ trickle charger (50mA) and let it charge over night. That would require a good 5V DC power supply and some electronics (LM317 + some resistors).

    http://www.angelfire.com/electronic/hayles/charge1.html

  13. Ilija says:

    Thank you for your help!

    So if I connect directly nokia charger witch have 3.6v and around 355mA, will led light work? And will not damage led light “bulb”? Thank you!

  14. robert says:

    The batteries may explode if you do that.

    You need a CHARGER, not a power supply. The control electronics for charging cell-phone batteries is usually in the phone. The “cell-phone charger” is just a dumb power supply.

    If you want to be safe, don’t do it.

    You need a circuit to control the current and to terminate the charging once the battery is full. Without that you create a fire hazard.

  15. Ilija says:

    We missunderstood. I want to connect nokia charger directly to led bulb not to the battery. So I only would like to know if the 3,7V and 355mA will not kill the led bulb. And if this is not good on what V and what A this led bulb is runing. Thank you!

  16. robert says:

    Ah, OK. That seems much better ;-)

    The solar cells provide up to 5.8V in sunlight, so the LED driver can handle that! If you google for “A705” you will find a datasheet, and in there it says that chip can handle up to 12V. As long as the batteries are removed, you should be fine if you power it with 3V to 6V.

  17. robert says:

    Just to make this more clear: you must connect your “charger” to the little circuit board shown in one of the pictures above. Connect it to the BT- and BT+ wires with correct polarity. The batteries must be removed.

    If you connect it to the metal spade connectors that appear when the whole battery/solar-cell unit is removed, you’re likely to blow the LED.

  18. eyob says:

    i just use ita battery for another perpes and i think the motherbord is damaged what shall i do

  19. robert says:

    Did you take it apart already? If so, clear photos would be helpful.

Comments are closed.