Copper tape on nickel strips for cell connection?

[toxie]

I'm planning on building a battery pack as soon as I get my spot welder. It's a Sunkko 709A, from other threads it sounds like 0.15mm nickel is the thickest I can hope to weld with it.

That's enough for my pack but I'd prefer to overspec the conductors more. Does it make sense to put copper tape on top of the nickel strips to increase current capacity? According to the 3M 1182 copper tape datasheet, it uses electrically conductive adhesive with 0.01Ohm resistance given a contact area of 1x1inches.

It sounds like a no-brainer, but is there any reason why people aren't doing this? There's lot of discussion in the welding thread about nickel thickness or using copper strips instead of nickel but I haven't seen anyone doing this.

Any reason why this would not effectively increase the current carrying capacity of my cell interconnections?

 

[amberwolf]

How much resistance does the nickel strip have? If it is less than the adhesive's resistance (assuming perfect application and no delamination over time), then most of the current will still be going thru the nickel, not the copper.

If you are terminating only on the copper and not hte nickel at the output points, then all of the pack current will flow thru the adhesive on the output strips. So you can multiply the current total for the pack times the total resistance of the contact area of one of the output strips (either + or - but not both), and get an estimate of the heat in watts generated inside the adhesive.

Keep in mind also that there will be a voltage differential across the adhesive from nickel to copper, whenever current is flowing thru the adhesive, so if you have humidity there will also be galvanic corrosion occuring--I don't know if there will be enough to be an issue or not, but it's another potential problem.


What you might consider instead is to punch holes in regular copper strips at all the weld points, so the copper is not in the way of the electrodes, and then solder the copper to the nickel strips before welding. (so you aren't heating the cells).

Then weld the strips just like normal, and still have the copper carrying more current thru at least the crossection on either side of the holes punched in it.

Or solder solid copper wire on either side of the intended weld area, before welding the tape to the cells.


Or, possibly, hole punch the copper to clear the weld areas, but then instead of soldering the copper to the nickel, flip it upside down so the nickel is on top, and then weld the nickel to the copper along it's length, then flip it back over and weld the nickel thru the holes to the cells.

 

[toxie]

Thanks AmberWolf. After looking into it more you're right, even though the adhesive has decent conductivity it's still so much higher than the nickel that not so much current will flow through the tape. As you say, soldering a copper wire to the nickel plate before welding is probably a much better way to go.

However, after looking into it more, I've determined that it makes more sense for me to buy a tiny generator to pack on the really long trips. I already have enough battery for all the riding I can do in one day (enough for 99.9% of my trips - I can go 120km on it at which point my ass can't take any more riding anyway), and in the remote places I'd like to camp for the other 0.1%, a gas generator gives me more freedom. Currently trying to get prices from local suppliers for a Yamaha EF1000IS.