Did the drill a hole through the board mod the other day. So a wire went right to the driver. Anyone have thoughts on the best copper braid to use? This cheap stuff I got probably wonât hold up. Pick up some of those copper springs too- have to order some stuff today.
fell, I use the same 22ga wire that I use for the leads to bypass the springs. Soldering it at the pad first, I try to put a slight coil to it before soldering it on top of the spring, this way it compresses inside the spring and should last indefinitely.
Ooo thatâs a good idea DBC. So coil it up and itâll act with the spring. Thanks Iâll start doing that 
You donât want too much or itâll clog the spring action.
Djozz, very interesting measurements ~0,3V voltage drop for 6A current makes such spring a nice heater :bigsmile: Some time ago Iâve done similar test (for current 3A) and I must tell that Your test doesnât include one, but very important parameter (surface of electric contact to battery cells terminal). It will be different for every spring (hard to calculate) but also generating voltage losses.
Thank you again djozz for your contribution to this community. 
Thx djozz,
that is very very useful testing.
I will braid even more springs from now on.
What we need is a spring that is composed of a spring steel core with a pure copper outer layer. And the copper layer needs to be more than just a coating. It needs to have some thickness to it. 
TY :-)
great test djozz!
(againâŠ)
Yes, I think surface area matters. Usually when braiding, I fill the top of the spring with solder then file flat.
very nice test, thanks for posting this
What I usually assume is that although the contact surface area may be very small, the resitance is also determined by the length of the narrow section. With two flat surfaces touching, that length is so short that the resistance is still negligible. If one surface is bended (the spring) the resistance may be a bit higher but still very low. Bocian, is there any measured data on this contact resistance? (there must be somewhere).
Thanks for the Test! I think steel springs are the best, gold plated or just simply plated. With the braid, (copper or the silver plated stuff), the spring can then be just what it is, a spring and the current will go through the braid. It will also help with heat stress on the spring, so a little longer life span for the spring. Excessive heat really kills those little springs. When you solder the braid on, you can always solder a copper button on top too, for a good smooth contact to the battery.
Hmm, good points OL.
Good call OL
I usually use a hobby file and smooth the solder joint on the braid, I can never seem to make it solder smooth, but a few passes with a hobby file and smooth as silk
Being a bit conservative, are you? 
I think that if you are DBCstm, TomE or Vinh, you are right, copper braided (steel) springs are the best for high drain hotrods.
On the other hand, if you are Old Lumens and into beautifully made moderate Nichia 219 mods, a clean looking phosfor-bronze spring like the one I tested is just great and mechanically thusfar it seems similar to steel (nice and stiff and 'springy'). At non-critical currents like 2 or 3 A this spring does help to get more efficiency out of the flashlight compared to steel springs, while copper braiding will not be drastically better but will look much messier.
the old dude can crank out some mean hot rods of his own! 
While weâre both here, can you fill me in on the kinds of problems youâve run into when soldering to steel springs? EG are there specific springs you had trouble with, was the trouble purely cold solder joints because of the way steel acts, does being plated help, etc. TIA