I blogged this subject recently, but I am now using a bigger lens. The 3 inch lens was having a difficult time heating the two leads. This time I used first a 4 inch lens, then a 8 by 10 inch fresnel lens made for reading a whole page.
The 4 inch lens was not much better than the 3 inch, but I think part of the problem is that I did this later in the afternoon with less sunlight, and the wind was blowing enough to cool off the wires as they were heated. Then I used the much bigger fresnel lens, and the solder melted easier, but the wind cooled off the wires as they were heated. The quality of the solder joint was not good, so I gave up and planned on trying it when it isn’t windy. It’s been windy the last few days, so I’ll wait.
I thought about this problem as I was trying to focus the light. What I need to do is enclose the work area with a box to keep the wind out. Also I should mount the lens on the box to hold it steady and at right angles to the sun. I could also put a window in the box to allow the work to be seen. I think it might be a good idea to make the window take out most of the sunlight like the sunglasses I wore. But the biggest problem is holding all the tools and parts in place. The parts need to be held where they are going to be soldered, but they need to be moved it relationship to the sunlight so the parts are in the hot part of the beam. And then when the parts are ready, the solder has to be added and the joint has to cool and be checked to make sure it’s a good joint. It would really help if I had an extra pair of hands!
Update Nov 23 – Today I used the big fresnel lens to melt a candle and spread the wax inside the compartments of a wooden battery holder I made. I use these for Joule Thief batteries, and occasionally a battery will get so discharged that it will leak. With wax in the cell compartments the cell fluid will dry up without soaking into the wood.
