Troubling spot welding with DN-5 0,3mm nickle band

J

Joost

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Mar 31, 2014
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Hello members,

After a long time I'm picking up my work to finish my diy battery pack.

A little history

One year ago I bought a secondhand escooter only for the LiFePo4 pack in it.
Now I haven test all the cells for there capacity and IR I can finally make a 28 Amp 48V battery pack!
It is maybe not a big pack but I'm happy that I can replace the dead gel accus!

The point were I need your advise is how to setup the spot welder?
I bought the DN-5 and a roll off 2Kg nickel band 10mm weight and 0,3mm thickness.
Now I have the problem to set it up right, one time it spot welding oke on a dead cell but the next try it will not work.
I've tried different 'stift' models from a sharp point to a flat square but nothing helps.

Can someone tell me the solution???



Can someone help me?


Ps: how many pressure is need to weld?
 
0.3mm nickel strip is actually quite thick for a battery pack, and you'll need a very powerful spot welder to weld that.

It requires a decent bit of pressure, but I suspect most of the current is simply passing through the nickel.

You can try dimpling the nickel before you weld so there are spots to help drive the current into the battery terminal, and you can also try splitting the strip on the end so there's no easy path through it (cut a slit in it, so it looks like http://www.ebay.com/itm/121555871670?_trksid=p2060353.m2749.l2648&ssPageName=STRK%3AMEBIDX%3AIT). That might help, but you may just be exceeding what the machine can reliably do.

If that's the case, get some thinner strip and layer it.
 
I believe a round tip and more pressure is going to work better than a sharp tip.
 
1/8" electrode with fully round tip is perfect.

You''ll want 1200-1500 amps for about 10-13 milliseconds.

.. 3 lbs or so pressure i'd guess. Helps a-lot to have dual pulse.
 
I don't think the DN-5 can source that much current...

You'd really be better off with some thinner strip for that welder.
 
Syonyk said:
You can try dimpling the nickel before you weld so there are spots to help drive the current into the battery terminal, and you can also try splitting the strip on the end so there's no easy path through it (cut a slit in it, so it looks like http://www.ebay.com/itm/121555871670?_t ... EBIDX%3AIT). That might help, but you may just be exceeding what the machine can reliably do.
Click to expand...
Joost- as long as you have the thicker material on hand, you might try these two tips and see how well they work. They should each have at least some effect to make the weld stronger. Most factory welded packs use a slotted tab which increases the path length from one electrode tip to the other by 5-10X and resistance scales with path length, so why not give it a try, it would only require a good snips or dremel tool if you want to be fancy about it. Less current through the tabs drives more through the welding site, as Syonyk said, and the dimpling further focuses the current from your welder. Dimpling could also be tried with just a nail and light tap from a hammer. If you try it, let us know how it goes!
 
By the way, here's a joke for the veterans to have a laugh at my expense-

When I first opened a DeWalt A123 pack to get the cells out, I thought the slots in the tabs were to save weight. :D
 
I'd like to get a laser cutter or something set up for cutting nickel sheet into patterns for pack rebuilds, but that's a bit down the road...
 
A little impression.

Every cell test with a Voltcrat/ELV ALC 8500 expert and a expert-2
After test program measured the internal resistances.

To day I go to buy a cut disk for my dremel to cut a smal ....(sorry for my bad English)
I hope to send some pictures tomorrow.

When I set de DN-5 on 10 of 10 will it burn a hole in the cell? A sharp point stift?
 

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The result of welding 0,3mm with slots.

DN-5 setup is 5 of 10
 

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Joost said:
The result of welding 0,3mm with slots.
DN-5 setup is 5 of 10
Click to expand...
That looks interesting, I've never seen a slot made in a continuous strip of nickel like that!

I'm not the best at judging the result from the photo, though.

Would you say the slots you made helped to create better welds?

You mention the DN-5 was set at 5, so you did not need to use full power to achieve these welds?
 
Yes with the slots iTS weldinding easier.
I die not try a higher setting because I had previously a bad experience by welding with as result the cell brokers and the internal material came out!!! So I'm a little bit fair.
 
I can't believe you connected cells in parallel with 0.3 mm nickel. That's pointless (except maybe on end groups) because there is no current flowing in parallel direction, only in series. So, you could have used 0.1 nickel for parallel, and 0.3 for series (or just solder some solid copper on nickel between cells).
 
riba2233 said:
I can't believe you connected cells in parallel with 0.3 mm nickel.
Click to expand...
I think he may just be proving the concept and showing what is possible, these may even be old / unusable cells. It's true that parallel connections do not need to carry anywhere near as much current as serial in a functional pack.

Joost said:
Yes with the slots iTS weldinding easier.
I die not try a higher setting because I had previously a bad experience by welding with as result the cell brokers and the internal material came out!!!
Click to expand...
It was nice of you to experiment like this and show all of us the result- thank you! Perhaps you could also try the dimpling approach and see how much affect it has on the weldability of the thicker nickel. I hope you are wearing eye protection and gloves, it sounds quite dangerous if the welder has penetrated a cell.
 
i already have mentioned in another thread that welding 0,3mm nickel can cause cell leakage.
the cans have a thickness of about 0,15-0,3mm (depends on manufacturer and also C-rate i guess) so you can imagine what will happen if you pull off the tab or if the battery vibrates a lot on the bike.
a short time ago i disassembled a ebike battery made of panasonic cells. i pulled off the 0,15mm nickel from such cell and it got leaky - even with such thin tab!

you should ask yourself if you really need 0,3mm. personally i think 0,15x10mm per cell in series is sufficient for most batteries made of 18650 cells. the distance anyway is so short that it will not add much to total battery resistance.
 
riba2233 said:
Yeah, you can weld cells in parallel using very thin nickel, and then you can solder solid copper wire between cells, on nickel tape. That will provide enough current carrying capability. Even 0.3 mm nickel is too thin for series connection, for most usages.
Click to expand...

why do you think that even 0,3m (i guess you mean 10mm wide) is to thin per 18650 cell?
the tabs used inside the cells are something like 5x0,1mm, so much less cross section there. im not sure what material this tab inside is made of, but one should be aluminum and the other something like nickel i believe.
when you relly NEED more cross section for series cell connection is if you take over 15-20A continuos per cell but than you should ask yourself if you not better use different type of cells or lipos (every 18650 cell on the market will anyway become to hot at such continuous currents).

again: the lenght of the tabs is SO SHORT it does add almost nothing to total battery resistance. calculate it. for instance 20s are about only 20cm lenght (1cm between the welds). thats only a few watts more or less losses.
 
Ok, you are right, it is enough, but only if you use it on each cell for series connection. It has resistance like 0.75mm2 copper, so if you have lets say 4P pack and you want to have 20-30 A system, you need around 2-2.5mm2 copper wire total, which is 0.75mm2 per cell.

And yeah, most chinese pack builders use few 0.15 mm nickel tapes for series connection on whole pack, and that is just silly, it gives terrible performance.
 
yes i mean 0,15x10mm per cell in series. for parallel connection 5x0,15mm sould be sufficienct or even less. you can weld it on top of the tabs for series connection, but make sure to only weld in the middle at the positive side not near the outside, because the shrink tube will melt below the weld and could create a short. if you use self sticking insulation washers it will give extra protection. from now on i will always use them on my batteries.

Joost, i would suggest you stop trying to weld 0,3mm nickel destroying your cells and messing around with cutting slots into the tabs. Take 0,15 instead and use time setting between 1,5 - 2,5 on the DN-5 (on positive side i always use a bit higher setting) and be happy ;)

edit:
there are also 0,15 tabs available on amazon (at least in germany) with nickel-copper alloy for better conductivity. i will try them soon and report here how they work.
 
riba2233 said:
And yeah, most chinese pack builders use few 0.15 mm nickel tapes for series connection on whole pack, and that is just silly, it gives terrible performance.
Click to expand...

What are the in-pack losses, in watts, for various amperages, with the packs you've looked into, and how would those change with thicker strips?
 
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