The Ikea "Godafton" block candle is a battery powered LED candle, with a timer function, 6 hours on 18 hours off.
These look pretty good, but they are known to be voracious battery eaters, 2xAAA. And thanks to the timer circuit, continue to drain the battery until it leaks all over the place.
So instead of throwing away the 6 candles I had, I wired then to a USB power source, to eliminate the battery limitation, and added a wifi controlled switch.
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Step 1: Safety First!
Safety first! Put on safety glasses, don't take them off until you're done! I don't want to hear any excuses. The combination of bad chemicals and little springs under pressure practically beg to flick something nasty into your eye.
Step 2: Clean Up the Mess
Corrosion and battery mess everywhere. Take out the batteries and put them in a bag for safe disposal.
Neutralize the corrosion with vinegar. Since the back cover took the brunt of the battery spill, I took it off and soaked it in a yogourt cup filled with picking vinegar. Look at the bubbles! Better living through chemistry!
Clean the terminals with a q-tip. You better be wearing your safety glasses! The damage ranged from bad to not much at all across the six.
Step 3: The Circuit
Two AAA batteries supply a voltage of 3V and according to the back cover, power consumption is 0.06W. Using V=IR and P=I^2R, I solved for a resistance of 417 ohms. The closest I had was 220 ohms.
Wiring up a test circuit, and measuring the voltage was about 2.5V. a little low, but it was working fine, so I can live with it.
Step 4: Wire It Up
I used some speaker wire I had left over for power wire. Soldering is hardly my strongest skill, but I got some practice here, do everything six times!
I also nibbled a corner out of the battery cover for the wires. So the candle doesn't sit funny on the wires, I got some stick on rubber feet.
I took a USB male to male, type A, cable and cut it in half. This made my two power wires, since I was going to set these candles up in a set of 2, with separate power supplies. USB power supplies the juice.
Tiny little wires, what a pain. I'm sure there are better suppliers of USB cables made for splicing into random projects, but my supplier is the Dollar Store.
Step 5: Testing
Remember, diode = One Way, so get it right before you stick it together. You can unstick it if its wrong, but its a pain, so get it right the first time.
Step 6: Done!
Yes! All done! Wires can be a pain, but no more batteries, and no more meltdowns.
Step 7: Make It Smart!
Since these are going to be put in an awkward spot to turn them off and one, I am using wifi smart plugs. I got these at Costco, CE Smart Home brand, and they work well. I'm sure the security experts are rolling their eyes at the gaping holes in my wireless security since I'm using these, but they work well, and they work now. In the future I would like to replace it with an ESP 8266 wifi module relay. But that is another project.
Step 8: Final Things
Some things I would have done differently. I wish I had used smaller wire in white or clear insulation. It would have blended into the background so much easier than "vibrant blue". But blue is what I had.
Using the cheapest USB cables as a power supply was not the easiest to work with. When I replace the USB smart plug with the ESP8266 relay, I will defiantly buy a USB Type-A cable with wire leads, no more “chop off the end and sort out the wires inside”. The wires are so fine, I am a little concerned that the connection won’t last very long before it fatigues and fails.
I checked the final voltage at the terminals, because the candles seem a little dim compared to what I remember. The candle has a circuit built in to make the LED flicker like a candle flame. The voltage is all over the place when I measure it, bouncing from a low of 1V to a high of 3V. I still don't know if the resistor I used was the right size. Unfortunately, the only other sizes I had was 1K ohms, 10K, and 100K.
Overall, I'm happy with the result.