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Busbar solder not sticking
#11
Sounds to me like weak flux or no flux unable to penetrate a thin veneer or something on the wire. Drawing wire makes it very smooth to begin with, so low surface area. Somewhere in the insulating process it's quite possible a thin layer of oxides, polymers, oils, glycol or other assorted schmutz got on there.

Make sure you're using 63/37 solder. Lead-free has issues. Make sure you're feeding the solder onto the copper, not onto the tip of the iron.

You may also want to try etching or acid flux. 85% phosphoric acid works wonders on 18650's. Smallish bottles are available as ice machine cleaner. 

One could also try the old technique used in gold damascening. Scratch the copper with a blade, creating tiny mountains and valleys, then lightly tap the wire with a hammer to bend the mountains over. Soldering would fill the valleys and create a mechanical bond in addition to the alloying bond.
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#12
(03-07-2020, 05:26 PM)drspeakman Wrote: Science experiment:

Created 4 small sections of busbar and soldered 3 small wires on each one, about same distance apart as would be between the cells in a pack, and all about the same length.

Bar #1 heated on natural gas burner on stove to remove any surface material

Bar #2 same as above, but scarified with a file over the areas soldered

Bar #3 no heat, no scarification, just soldered

Bar #4 no heat, scarified, then soldered

Result:  Only failure to stick well was preheated and not scarified busbar.  Stuck very well on untreated copper wire, scarified untreated copper wire, and on scarified preheated wire.  I am going to discontinue any pretreatment except to scarify with a file.

So, my next thought is that I may be causing the soldered areas to unstick when I am adding the extension to the busbars with a copper pipe butt splice.  I use a more malleable 10 gauge stranded copper wire to extend the busbars and then add Andersen connectors on the ends.  I use a blow torch to add solder into the ends of the butt splices after thoroughly crumping over the wires.  It may be this heating process to add solder into each end of the butt splice that is extending down the busbar and causing the soldered areas to loosen up.  At least this is my current working theory.  I am going to do this process first, and then do the soldering of the cells to the busbar as the LAST step, hoping this will eliminate the issue.


No need for all that mumbo jumbo. If you just stripped the romex, it should be fairly clean. No prep needed. Use a high wattage iron with a broad chisel tip. 3 12ga wire is pretty thick. You're just trying too hard with an underpowered iron that is not transferring the heat fast enough to localize the heat. Your solder welds will look like a mess if there wasn't enough heat.

https://www.amazon.com/Weller-9400PKS-Un...B00CLU255A
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