18650 21s15p - 3 layers of 7s (balanced separately) advice

[izeman]

Once you use one you’ll see the difference.

Even though i agree to prefer a soldering iron with a wide tip, i think those soldering joints look perfectly fine to me.

 

[smeagol222]

I got the iron!

It does have a wide tip most of the heat comes when i lay it flat, I can use the corner. Might have to get a smaller tip

It’s a lot easier to work with since it’s so lightweight. It takes a while to warm up- also I just need to remember to unplug it [emoji16]


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[litespeed]

Awesome. You most probably will never have to worry about a cold solder joint ever again.

Congratulations!

Tom

 

[bobmutch]

The THICK yellow wires are the ones that carry all the current. The thin long blue one carries almost NO current.
See how i did it with my pack. I just used 24mm wide 0.15 strips. Btw: The thick red main wire was soldered FIRST to the nickel strip, then the nickel strip was welded to the cells. So no heat was put into the cells.

I like the plates, 0.15mm plates are 18mm and good for 18A, the 0.2mm plages are good for 1.33 times more or 24A.

I like how you did the POS exit-wire by splitting the wire and soldering the braid pre-welding. Lots of guys are laying the whole wire down the length of the P-group but have there exit-wire at the end. having it in the centre is for sure an improvement.


I suggest spreading a split wire over every 2 cells, having the shielded wires all the same length and connect them all into a connector of appropriate Amp rating. So on your 6P here you could use 3 wires of appropriate AWG and connect them together and the same on the POS.

Also I like to see you don't believe in parallel busbars.

 

[bobmutch]

I don't have as much experience as you do so...

but I don't think they that the current which travels serial from cell to cell is not going to take the long way around and go from the cell over to half way between the next cell in it's P=group then across the copper wire back to the 0.15x7mm strip then to next cell, I think it would be better if solder the wire on top of the nickel strip or well another strip on top. The current will take the most direct path, or should I say the path of least resistance, how ever as heat goes up so does resistance and if the nickel strips heats up high enough and the resistance goes high enough it will then move over to the wire you suggested between cells which is a longer path but a lower resistance. Is my position correct in your opinion.

Better, but yes I know to late, would be to use 0.2 which give 9A on a 7mm strip or better yet use a 0.15 plate and get 18A (18650s are 18mm wide, 1A per 1mm width on a 0.15 thick strip, 18A) there P-group cell, or even 0.2mm plate which is good for 24A per cell (18650s are 18mm wide, 1.33A per 1mm width on a 0.2 thick strip, 24A).