# LED fairy lights with series capacitor?

I've opened up the battery box of a string of fairy lights (like pictured at bottom) and found a resistor, plus what looks like a capacitor in series with the lights. Is this really a capacitor? If so, how does it work in a DC circuit like this?

simulate this circuit – Schematic created using CircuitLab

My aim is to convert these to run on 12v. Does this circuit look ok? How can I determine the right value for the current limiting resistor?

simulate this circuit

• A capacitor there would cause the led to shine for a very short time until the circuit is turned off. Maybe it's a resetable fuse. I don't know. To make a 12V circuit, the total of the series must make 12V. If there are 4V LEDs, it's OK with a 10 ohms resistor, if they are 4.5V LEDs then it could be a bit dim, but also OK. with no resistor. As they are powered by 3x1.5V batteries they can be 4 or 4.5V. May 24, 2020 at 23:11
• That's what I thought about the capacitor too but they don't dim at all. Maybe it's not a capacitor?
– Jake
May 26, 2020 at 3:12
• It can be a resetable fuse. May 26, 2020 at 17:04