I have a 5V 1500 mA charging/power cord for a camera that was too short to reach the mounting position I need, so at the suggestion of my electrical engineer father, I decided to try to lengthen it. He said to just twist and tape the wires together but I wanted a sleeker look so I decided to try soldering and heat shrinking. The cord will be left plugged in and powering the camera 24/7. The original cord is 20 awg but the closest I could find was 4 extra feet of 18 awg lamp cord (2 wires in both). So I cut the original, stripped the 4 ends between 1/4 - 1/2 inch back, spread the strands out, butted and twisted them.
Next, I soldered them together and this is the part I feel uncomfortable with. For starters this was only like my second time ever soldering and the first time with this iron. The first joint looked ok, maybe slightly light on solder - it didn’t flow very well - but it was holding together against a gentle tug. The second was my worst joint, it ended up with a little too much solder and kind of thick. I figured out that my iron wasn’t hot enough even though it was set at about 380-390. After turning up the heat, it flowed into the next two, but the tips of the insulation on the original wire melted a tad (see photo). Is that bad?
Next I applied heat shrink over each individual joint. The heat shrink seemed a little thin so I also wrapped a little electrical tape around one joint on each end of the spliced length for extra insulation. Then I applied larger heat shrink over both wires together on each end. Then finished it off with white electrical tape just to match the cord color.
My question is, is this safe to use? I tried plugging it in and the device indicates it is charging. I feel pretty confident it’s not going to short with two layers of heat shrink and electrical tape separating the conductors. But being a novice, I’m just looking at my taped up cord picturing a fireman holding it up for a look in the remains of my burnt home. I’m most worried my solder joints aren’t good enough and might cause a dangerous resistive connection.