Recently I was approached by a younger user of the Duktig toy kitchen. It includes a battery powered stove top which seems to chew through batteries (6x AAA) like mad. There is a replacement PCB available that cuts down the power usage, but unfortunately it costs quite a bit when imported to Germany.
So I decided to go with an easier route and power the toy kitchen from a power adaptor („wall wart“). I wanted to share what I find to work pretty well:
Using the instructions from the Ikea Duktig Stove Battery Saver site it was easy to open the plastic tray (remove the top at the longer sides first then on the other sides). The original plan was just to add a barrel connector to the stove top, but it turned out that the circuit needed an additional 6V supply (in the original Duktig this is done by running an extra wire from the positive terminal of battery 4).

My solution: adding a simple voltage divider to create a 6V voltage source from the 9V. My estimate was that about10mA would be enough current for the circuit, so went for 270 and 560 ohms.1 Naturally you want to check the total current, resulting voltage and dissipated power in each resistor:

I_total=9V/10.8mA,
U_divider=(560/(270+560))*9V=6.7V,
P_R1=31.7mW, P_R2=65.8mW.

I then connected the whole thing up: the (-) terminal of the barrel connector to the matching terminal on the battery compartment (using some piece of leftover wire), did the same with the (+) terminal. Then I connected both resistors on one end and soldered the whole thing straight over the back of the battery compartment (560ohms resistor on the negative terminal and the 270ohms end at the positive terminal).2 The middle of the voltage divider then was connected to the extra 6V terminal of the battery compartment.

The hack works pretty well so far. To prevent anybody from using batteries and a power adaptor at the same time I desoldered one of the gray wires that connects the single batteries in the compartment. An additional note in the battery compartment explains that batteries cannot be used unless the modification is reversed.

Here is the bill of materials that I used in the end:
– 9V power supply (mine was 900mA but I guess 300mA would have been enough)
– barrel connector (matching the power supply)
– 270ohms resistor
– 560ohms resistor
– 3 pieces of wire

1. both are included in the E12 series i.e. not hard to find [↩]
2. unfortunately I did not take pictures [↩]