Anyone know where I can get braided copper wire for doing tailcap mods.?
I have been using solder wick. The stuff without rosin. Not sure if that answers your question
i use 18 or 22 AWG silicon wire - mostly outside the spring.
seems more flexible to me…
If you have any discarded computer speaker connector wires, microphone cable, dead headphones/earbuds check them for shield braid.
I have solder wick, but it gets real hard when i solder it. I cut a couple pieces off some old brushes from a grinder that worked great. Would like to find more like that.
Yeah, solder wick gets hard. That is because when you solder the ends, solder wicks up into the length of it. 
What I do is cut it a little long and “Scrunch” it up a little as to separate the strands so that the middle isn’t able to wick. Actually I don’t like using it and I think I will give M4D M4X idea a shot.
Mechanical: Take a paperclip. Bend it. Unbend it. Repeat until mechanical failure. Doesn’t take all that long, does it? Now, repeat the experiment — with the ends at the same points as before (imagine you’re connecting two things) — only this time, leave a bit of “bow” or bend & twist it to the same degree as your bends in the first test… Lasts a bit longer, doesn’t it?
This is why, if you ever look at the door of an electronic equipment cabinet, at the Ground Strap, you’ll notice it has a large bend, much larger than needed. As the door opens and closes, the mechanical stresses on the Ground Strap are spread along the length of the wire, not focused on a bendy spot.
M4D M4X seems to have grasped this intuitively (or it was beaten into him as it was me) which will keep his spring mod happily conducting for a long time.
Electrically, it’s purely a matter of wire cross-section / joint contact. If you find a Solder Braid and a Stranded Wire with the same net diameter, you should see the same I (or R, whichever way you look at it) through them both, assuming the same quality of solder joints. It wouldn’t be hard to find that the spring itself conducts ~as much as the wire you’re using, especially with Cat3 or Cat5 LAN cable. Obviously, you’re looking at 1/R1+1/R2 so it will help, but how much help vs. how much work?
Solder: Yes, Solder Wick is made to suck up as much solder as possible, but as dchomak pointed out, that propensity can be easily defeated. It’s not just with wick, though… If you look at M4D M4X’s picture, you’ll see exactly the same effect at the PCB end where the solder has “wicked” into the braided wire sufficient to cause that end not to bend around the spring for a few mm.
Corrosion?? I’d opine that bi-metal electrolysis has more of an affect on circuit performance than silver tarnish or copper fouling, but that’s for the real Engineers to work out. I’ve never seen any corrosion on mine, now that I’ve sworn off Alkaline batteries, so IDK.
As for me, not that my opinion matters, but I like the way Solder Wick flexes more easily than rubber-bound twisted wire. Plus, most of my “hobby” wire comes from LAN cables too, which is SOLID and will break like that paperclip, and that right soon. I load the end with a good solder blob, then wind the braid around a #0 Phillips screwdriver to give it that flexy “pigtail”. This goes inside the spring & when I push the solder blob into place it “un-scrunches” (props to dchomak) enough to defeat the wicking action. Then when tinning the tip, I use a heat sink (hemostat) to prevent that wicking & do the same un-scrunch trick to attach the wick to the spring.
Here’s something I believe I can see the results of: at the spring tip, after it’s soldered up & cooled, I melt-&-quickly-stick a good-sized solder blob onto the spring tip then flatten it with smooth-jawed pliers. It seems to get a larger contact area on the battery, and does seem to make the light a little brighter.
No, none of that is going to solve anybody’s problems, but I wanted to throw in my 2 cents…
HTH!
I use 22AWG with the wire inside the spring, the thing with copper braid is they don’t last very long, but I use them in my hot rod mods that requires a shortened spring.
I’ve been using the method of drilling a hole through the PCB and running a wire directly from the top of the spring to the switch.
Now that everyone has switched over to HDMI and DVI cables, you probably have some old coax cable sitting around. The old cables with the BNC connector on the end? Push and twist a quarter turn? That’s coax cable, RG6, RG59… all of it has a braided shield just inside the outer jacket. It might take some work, but harvesting that from your old antennae and cable TV cables should get you plenty.
The braid on cable-TV coax is aluminum and there’s glued foil involved too. Not worth bothering with. RG 178 coax like most wi-fi cables have should be great for smaller braid, but solder wick is much, much easier.
Phil
I’ve found it a lot easier to put a wire of 16/18 gauge outside of the spring than anything inside of it. I also try to extend the braiding wire right across the top of the spring when soldering and, file it flat to have as much surface in contact with the battery as possible.
Great thread. When I use copper braid I first cut a 2” length, pull it hard to get it narrow then solder one end. Now trim that end so there’s only a thin strip of solder left. Now I add flux to the base of the spring, slip the braid inside and quickly solder it to the spring base (you don’t need to add more solder if you use flux). Finally I push some braid down inside the spring, then solder the end across the spring top (use flux and as little solder as possible) and trim square. The braid has plenty of flex and good contact.
Great! I’ve got several hemostats in my kit, never thought about using them for heat sinks… Thanks for the suggestion!
It also helps round out the point of the spring so it won’t scratch your cells… I’ve used this trick when I can’t conveniently bend the sharp end point back into the spring.