Max current through a spot welded connection?

[ScotY]

I tried searching but didn’t come up with much. I will be building an 8s2p Molicell P42A pack. The current draw will be about 90 amps, but just short duration bursts of maybe 5-7 seconds. I am confident I can solder these cells together with minimal heating. But I have a Kweld that I can use. I’m lazy so would prefer to spot weld but am unsure about which way to go.

I thought maybe I could use some household 12 gauge solid copper wire to solder the cells together.

Or I have on hand 0.15 and 0.2mm nickel 8mm wide. I have some 0.2mm copper sheet. So could try some combination of this using the Kweld.

I’ve never really seen anyone test high current draw on spot welded connections. The solder is best guys will say it’s a bad idea, I’m sure. Yet, every high C lipo pack I’ve taken apart has some spot welds on the tabs.

I’m so undecided…someone please help me! :lol:

 

[calab]

It is easier to solder cans that already have the spot welding tab on it. I seek those out for ghetto diy builds. You can buy cans with them already on, or go by way of tool pack batteries from Home Depot/Lowes.

Max current through a spot welded connection depends on the surface contact of the tab welds themselves, and how many spot welds there are, the thickness of the tabs themselves if they are coated or pure. Lots of things to consider but I'd be interested to know if anyone posts something up.

Remember it can be a bit tricky to solder directly onto the can itself, one side may be easy but like a123's the solder dont always stick if you dont use the proper flux, proper solder and proper prep, and most importantly the proper iron temperature and wattage for the solder your using, for a good wetting action. Too little a tip, not much heat transfer action, too big a tip perhaps the iron is over-run and cant keep stable temp.

Lots of factors in the equation you seek friend.

Just find the general rule of thumb for the thickness of the tab, what the tab is made out of, coated or pure, and make sure your tabs stick, and slap on 4 or 5 or 6 tab welds depending on area, if theres a slot in your tabs like the premade ones sometimes are then make each side even on both sides of the tab slit for the one can.

 

[ScotY]

Many years ago, we used to solder nicad cells end to end. I’m sure that’s now a lost art. :lol: I’ve found sanding the can, good solder/flux, and a good iron with a very large tip will work great. And good technique also. I’m not worried about being able to solder them.

I’m just wondering if anyone has some data from testing spot welded tabs at higher current levels. Most batteries used for ebikes, etc. need the range so the overall current draw through each paralleled set might not be particularly high in many applications. I’ve always wondered just how well spot welded connections fair.