Help Selecting Strips for 60 A Continuous Discharge

[YoshiMoshi]

I took a look into Matador's excel sheet. Some of the math I was able to conclude where it came from, but most of it I was.

I'm using the following spot welder:

Would I be able to use this spot welder to spot weld 0.1 mm thick nickel strip and 0.1 mm thick copper strip together to a 21700 cell, and then sandwich another sandwiches ontop of this?



It looks like 0.1 mm thick nickel that is 11 mm wide and 0.1 mm thick copper that is 11 mm wide can be spot welded together to give me a total ampacity of ~21 A. I can then spot weld two additional sandwhiches together to give me 3 copper strips and 3 nickel strips spot welded to a cell, giving me an ampacity of about 63 A?

Is there a better way to do this? Thanks for any help!

1) Place 0.1 mm x 11 mm copper strip ontop of cell.
2) Place 0.1 mm x 11 mm nickel strip ontop of the copper strip
3) Spot weld the two strips of metal ontop of the battery.
4) Place 0.1 mm x 11 mm copper strip ontop of nickel strip.
5) Place 0.1 mm x 11 mm nickel strip ontop of the copper strip
6) Spot weld the sandwich to the other sandwich
7) Place 0.1 mm x 11 mm copper strip ontop of nickel strip.
8) Place 0.1 mm x 11 mm nickel strip ontop of the copper strip
9) Spot weld the sandwich to the other sandwich

 

[harrisonpatm]

It's good that you're doing your research before you dive into it, so hopefully my comments won't dissuade you from attempting your build. Keep in mind that assembling a DIY pack is hard, and assembling one of good quality is even harder.

That spot welder you linked is unlikely to be of any quality at all. It might have enough juice for spot welding .1mm or .15mm copper. It almost certainly will not be able to manage a copper/nickel sandwich. Most of us on the forum who build our own packs either use Kweld or huge transformer-based spot welders.

.1mm copper is really quite thick. Even with a quality spot welder, copper is going to dissipate heat very well, and you will need to go thinner on the copper, thicker on the nickel (or nickel-plated steel). Have a good read through the copper-nickel sandwich thread, you might find methods that would work for you. For reference, I used 0.2mm nickel + 0.07mm copper in my last build, basically just copper tape.

Finally, your proposed method is essentially 6 separate sheets of metal. This is not a great idea. The idea of using copper/nickel sandwich is to be able to get enough current carrying capacity in just those two materials, and nothing more. Stacking on top works in theory, but in practice you're going to be getting diminishing returns. Plus more welds that have a chance of coming off during riding.

Would you be able to get some scrap 18650s and try building some test packs to get a feel for it before you do your main pack? It's a difficult task, and might take some practice.

 

[YoshiMoshi]

It's good that you're doing your research before you dive into it, so hopefully my comments won't dissuade you from attempting your build. Keep in mind that assembling a DIY pack is hard, and assembling one of good quality is even harder.

That spot welder you linked is unlikely to be of any quality at all. It might have enough juice for spot welding .1mm or .15mm copper. It almost certainly will not be able to manage a copper/nickel sandwich. Most of us on the forum who build our own packs either use Kweld or huge transformer-based spot welders.

.1mm copper is really quite thick. Even with a quality spot welder, copper is going to dissipate heat very well, and you will need to go thinner on the copper, thicker on the nickel (or nickel-plated steel). Have a good read through the copper-nickel sandwich thread, you might find methods that would work for you. For reference, I used 0.2mm nickel + 0.07mm copper in my last build, basically just copper tape.

Finally, your proposed method is essentially 6 separate sheets of metal. This is not a great idea. The idea of using copper/nickel sandwich is to be able to get enough current carrying capacity in just those two materials, and nothing more. Stacking on top works in theory, but in practice you're going to be getting diminishing returns. Plus more welds that have a chance of coming off during riding.

Would you be able to get some scrap 18650s and try building some test packs to get a feel for it before you do your main pack? It's a difficult task, and might take some practice.

Thanks for your reply! I did find an old battery pack Milwaukee V18 series at the dump I was going to practice with after verifying the cells are dead.

I see on the nickel copper sandwich thread that the current chooses the path of least resistance, the copper, and that the nickel just acts as a media to allow the welds to occur. So basically the nickel is not a conductor.

Given this information, it's basically impossible it seems to create a 60 a continuous discharge current battery pack for a power tool? I don't think there's a configuration of strips that would work unless they were incredibly thick or wide?

 

[gromike]

With that welder you won't get far, as to the welding you plan to do. Build you some batteries and see how it goes.
I sure hope you know about arcs and sparks. Wouldn't want to burn off your nose and finger tips.

 

[YoshiMoshi]

With that welder you won't get far, as to the welding you plan to do. Build you some batteries and see how it goes.
I sure hope you know about arcs and sparks. Wouldn't want to burn off your nose and finger tips.

I do know about arcs and sparks. Any tips on how to avoid them?

 

[harrisonpatm]

Sometimes there's no avoiding them. Wear safety glasses while assembling.

 

[YoshiMoshi]

Sometimes there's no avoiding them. Wear safety glasses while assembling.

Thanks for all the input and help with this.



So given the information from that copper nickel sandwich thread, the nickel isn't a conductor, and is mearly a means for getting the weld to occur. If I assume 21 mm is as wide as I can get without going over the width of the battery, and 0.1 mm thickness is the max I can reasonablly spot weld. A copper nickel sandwich would not work because 21 mm wide 0.1 mm thick copper only has an ampacity of about 27.6 A



Playing around with the thickness of nickel. 15 mm and 20 mm width are really the only common sizes greater than 15 mm wide. I cannot for example find a 19 mm wide strip for sale on Amazon.

Option 1
2.2 mm x 15 mm Nickel strips. At 0.2 mm thick strips, this would be 11 strips!

Option 2
1.7 mm x 20 mm Nickel strips. At 0.2 mm thick strips, this would be 9 strips!

This is for a power tool battery pack. 5S3P. Would I ran into problems with Option 1 and Option 2 above given how many strips would be requried?

For the series connections
Option 1
Connecting 3 cells to 3 additional cells. I could do 3 stacks of strips, 4 strips thick
Option 2
Connecting 3 cells to 3 addditional cells. I could do 3 stakcs of strips, 3 strips thick

For the B- and B+ connection though, I only get one stack of strips. So I persume I would need to use a wire instead of nickel strips to make the connections? 11 strips thick or 9 strips thick seem like too much and not feasible? But even with a copper wire, it looks like the thinnest wire I could get would be 6 AWG wire with 75 deg C (65 A ampacity) or 90 deg C insulation (75 A ampacity). But 6 AWG wire is 4.11 mm thick, and thicker than simply using nickel strips in Option 1 or Option 2.

 

[docw009]

I've wasted money buying several portable welders with one or two integrated LiPo pouch cells, After a few charge cycles, the cells lose their discharge capacity and won't even weld the easy to weld .10mm nickel plated strips originally included, For this project, you need a better welder.

Sure, the nickel is a conductor in a sandwich, if you run it in a parallel layer. I know many users just use it to anchor the copper welds. And why use strips when you could make the conductor 3 cells wide? I don't see why you are talking up 11 strips.

For 60A, that;s 20A flowing per cell, anyway.




60A thru a 5S-3P is 20A per cell.
.

 

[YoshiMoshi]

I've wasted money buying several portable welders with one or two integrated LiPo pouch cells, After a few charge cycles, the cells lose their discharge capacity and won't even weld the easy to weld .10mm nickel plated strips originally included, For this project, you need a better welder.

Sure, the nickel is a conductor in a sandwich, if you run it in a parallel layer. I know many users just use it to anchor the copper welds. And why use strips when you could make the conductor 3 cells wide? I don't see why you are talking up 11 strips.

For 60A, that;s 20A flowing per cell, anyway.


View attachment 361506

60A thru a 5S-3P is 20A per cell.
.

I think the battery pack you point to is a Makita battery pack, with rated maximum continuous discharge of 60 A.

While each cell is 20 A, I believe the B+ and B- connections see the whole maximum current discharge of 60 A? How should I make the connections for the B+ and B- connections?