Spot Welding Copper Strips to 18650 Battery Cells

Those welds look really nice. I just looked into this material, but it appears to have a significantly higher resistance than all the other alternatives.

COPPER 1.7 x10^-6 Ω.cm
ALUMINIUM 2.6 x10^-6 Ω.cm
ZINC 6 x10^-6 Ω.cm
NICKEL 6.9 x10^-6 Ω.cm
IRON 9.7 x10^-6 Ω.cm
NICKEL-SILVER 28 x10^-6 Ω.cm

https://www.rfcafe.com/references/electrical/resistivity.htm
https://calfinewire.com/datasheets/100146-nickelsilvercda752/

EDIT: added second reference for nickel-silver resistivity
[/quote]

Correct. I apologize for not updating my post. I found out later that “Nickel Silver” does have a higher resistance so it would NOT be a good option for high current applications. I remember thinking “these welds are too good to be true”. Guess what? :oops:
 
kdog said:
Hey garolittle
Whats the conductivity? IACS?
Cost? And where did you get it.
Cheers for info.
Click to expand...

Hey Sir. I apologize for not updating my post. I found out later that “Nickel Silver” does have a higher resistance so it would NOT be a good option for high current applications.
 
I'm looking at ordering a spot welder. Is there anything cheap(< $300) out there capable of welding the following strip:

https://www.ebay.com/itm/133104900615?ul_noapp=true

I'd rather not experiment with building my own spot welder at this time as I just want to get this pack put together with minimal troubleshooting and get my project moving under battery power. I am using A123 26650 cells, and I am building a 24S4P pack of them. I plan to run them at 96A peak, and my BMS is rated for 100A pulse/50A cont.

If there is nothing appropriate within my price range, I'll probably have to go the DIY spot welder route, and delay getting my project running on batteries yet more.
 
Kweld is probably best at that price point but 0.3mm copper could be too thick for it. Depends really how thick the nickel plating is on that strip. If you buy kweld for that job you want to go for dual lipos that will give close to 2000A weld current and thicker leads on electrodes to have any chance. Go take a look at the thread..
 
no chance with kweld welding copper. i tried 0.1mm strips and doesnt work.

btw: you need a bit of resistance in your setup. if you go dual lipo with bigger wires your resistance is that low that you trip the 2000a limit easy.
that means it doesnt work if you wanna stay in warranty limits.

btw: the single 3s6000 graphene lipos do allready 1700A on setup. the 2nd in parallel is good for welding longer times. wires heat up way more than a single lipo.

for extended lifetime of your lipo i would recommend always 2 of them parallel or bigger ones like 3s16000
 
Merlin, have you tried the copper/nickel sandwich method. I highly recommend it for series connections.

0.20mm thick copper on the cells, and 0.15mm nickel over it. The nickel provides the resistance, and that size copper can easily handle 30A peaks, possibly more.

Copper is four times more conductive than nickel, so 0.20mm copper is equal to 0.80mm nickel...plus less heat.
 
Interested because I'm either going to use .3mm copper / nickel coated spot welded, or just use plain soft copper and physically compression sandwich it like Kohlme did for his 26650 LiFePO4 pack.

I'd prefer welded. I think the positive terminals should be doable, but am concerned about the negative side blowing though. I've been saving junk AAs to practice on if/when I go the welded route.
 
spinningmagnets said:
Merlin, have you tried the copper/nickel sandwich method. I highly recommend it for series connections.

0.20mm thick copper on the cells, and 0.15mm nickel over it. The nickel provides the resistance, and that size copper can easily handle 30A peaks, possibly more.

Copper is four times more conductive than nickel, so 0.20mm copper is equal to 0.80mm nickel...plus less heat.
Click to expand...

not tried yet but interessting.
what kind of batteries do you build? i do 95% of all batteries with nickel sheets 0.2mm.(not strips)
for example surron packs 20s15p. those doing 300A battery current. i have temp sensors installed between, above and on +/- wire exits to monitor temps in real world usage.
whole pack with vtc6 is at 28mΩ. from specs i would miss the point of that extra work having 0.8mm nickel/0.2mm copper.

but of course evs/batteries in this smaller category cant run that massive amps continue. In real world usage i wouldnt talk about more than 20A continue for VTC6 without cooling solution.

less resistance is always nice but if the cells anyway heat up before just because of usage its hard to find the benefit of extra layers.
if i could use copper sheets i wouldnt go above 0.1mm because of the way better conductive material.

from experience even from those who ride their surrons at 50-60wh/km continue whole battery stays below 40°c. Thats pretty nice to me.

not sure even if could weld pure copper without nickel what happend overs years about humidity and copper inside a battery.
 
Or... this approach looks very robust and easily made to carry the 350A surge current I'm designing for (borrowed from spiningmagnet's ebike site :D )

Spot weld the strips to the buss bar, then attach the strips to the cells.

BatteryBusStyle1.png
 
Using copper buses reduces voltage sag and waste-heat from the watts flowing through nickel. Of course, copper by itself cannot be welded onto a cell-end, so just put a 0.15mm nickel cap over it.

Try it on a bad cell, then check the resistance of a copper nickel sandwich, compared to thick nickel (0.25mm/0.30mm?)

The parallel connections can be pure nickel. Even 0.10 or 0.15 will work fine for paralleling.
 
hallkbrdz said:
Or... this approach looks very robust and easily made to carry the 350A surge current I'm designing for (borrowed from spiningmagnet's ebike site :D )

Spot weld the strips to the buss bar, then attach the strips to the cells.

BatteryBusStyle1.png
Click to expand...

Nice! :D
 
I assume the KWeld people are on holiday? Figures, finally have all the battery parts and nothing to assemble them with.

I'll be using 0.032 inch buss bars for the 4x5 groups with 0.08 inch bars for the 2x10 groups. That should prove adequate for my average current requirements along with 1/0 supply wires.
 
Wow. Great thread. Remind me never to go over to Facebook ES. It’s not the same professionalisms as here. Just my opinion......

I purchased 1,000 Tesla 2170 cells. 21700 ....
And I’m going to try my hand at a 4 or 5p 14s
Pack for my Framed Alaskan Fat Bike Build.

The other cells will be for a power wall or an EV car or Motorcycle....

I purchased the Kwelder..... I have 12v 9.6ah A123 LiFePO4 packs that do not voltage drop with a 5-7C load 45-65 amps.

How many Should I put in parallel for the Kwelder?
I’m sure each pack can peak at 200-400 amps

I’d like to do the Sandwich technique.
Is there another thread just on this???

Thank you.
 
hallkbrdz said:
BTW - Keith said the KWeld kits won't be back in stock until the end of September. No details as to why.
Click to expand...

mine has shipped :)
 
I’d like to do the Sandwich technique.
Is there another thread just on this???

Thank you.

I have 21700 cells arrived today and the Kweld.
Now I need to wrap my head around the supply for the Kweld.
I have lots of 12.8 Nominal LiFePo4 9.6ah packs. at 45-65 amp draw, they maintain their voltage to 3.2v per parallel group within the packs(has jst's to monitor) I believe they can 250 or 400 CCA PB equivalent.

Kweld manual says 4-30V input 2,000 amp max so I'm thinking of putting two of my 12.8v nominal A123 9.6ah packs in series for 8s or 25.6V Nominal with still a CCA of 250 or 400. I might need to also run some more in Parallel too.

Any insight on using LiFePO4 on Kwelder????

6OBHGG5WRuOl0US2hgIcrA
 
Tommy L said:
I
Kweld manual says 4-30V input 2,000 amp max so I'm thinking of putting two of my 12.8v nominal A123 9.6ah packs in series for 8s or 25.6V Nominal with still a CCA of 250 or 400. I might need to also run some more in Parallel too.

Any insight on using LiFePO4 on Kwelder????

6OBHGG5WRuOl0US2hgIcrA
Click to expand...
Do not go over 12v, start with 2 packs in parallel, those are 120A max cells, so you end up with 960A capable pack. Limitation will be the nickel connectors.
P. S. If those are cut 36v medical packs, filter out the block with the fuse weakened tab.
 
parabellum said:
Do not go over 12v, start with 2 packs in parallel, those are 120A max cells, so you end up with 960A capable pack. Limitation will be the nickel connectors.
P. S. If those are cut 36v medical packs, filter out the block with the fuse weakened tab.
Click to expand...

My Pre-made packs are from 8-9 years ago. I believe the A123’s in them were 30amp max with a near zero volts @ that load individual cell test. I’m sure there’s a high resistance on the strips they used. But on my testing back then, no voltage drop pulling 5-7C on the pack. No speed drop over time use of the packs. I would just run Four or six or eight in series for what every i was running at the time. I used a 4 packs in series 51.2v nominal and 4 in parallel 38.4ah for a 2kw pack on my electric lawn tractor conversion. Zero voltage drop.

So I’ll start with two packs in parallel and see if it works. I might need four or eight in parallel.
I’ll just add one at a time.

I don’t want to over current the Kwelder either.
Just how will I know??? I do not want to blow it up. Lol. 🙏🏻🙏🏻🙏🏻🙏🏻

[youtube]ygu8bV423wU[/youtube]
 
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