Soldering tab-less 26650VT ok?

[dscline]

I have a bunch of these batteries I need to build into a pack. They have no tabs. How much risk is there is soldering copper strap directly to the batteries? If you solder quickly with enough heat, will they be OK, or are you likely to damage the batteries?

 

[tostino]

I have a bunch of these batteries I need to build into a pack. They have no tabs. How much risk is there is soldering copper strap directly to the batteries? If you solder quickly with enough heat, will they be OK, or are you likely to damage the batteries?

I soldered nearly 100 18650 batteries into a pack earlier this year. I don't see any damage at all, or any loss of capacity. Like you were thinking, I used lots of heat, and made a quick connection.

 

[MitchJi]

Hi,

You could also use Dewalt end caps for solderless connections as done by gary.

shown here:
http://endless-sphere.com/forums/viewtopic.php?f=14&t=2498&start=375#p136993

and here:
http://endless-sphere.com/forums/viewtopic.php?f=14&t=2498&start=375#p137198

 

[heathyoung]

Depends on the chemistry really - I wouldn't attempt it on a volitile lithium chemistry thats for sure.

 

[drewjet]

I soldered 216 of them with no issues. 3600 miles and counting.

You need a high watt (100) solder Iron. I got one intended for stained glass. Solder quick and then quench with a damp rag.

Awesome batteries.

 

[onemintyulep]

I just made a pack out of these. Used my wifes Tiffany-glass soldering Iron. You need a FAT tip on a 100 Watts iron. Roughen the cells with sandpaper. Then first tin the cells. Do not take longer than 2 secs. Use solder wick to connect the cells, afterwards tin the solder wick completely to minimize resistance. If you do it like this - no problem at all.
Make sure to connect the parallel cells first and charge these to 4.1V, then make the series connection.

 

[frodus]

Anything less than 100W would be too cold to heat quickly. If you're holding the soldering iron on there for more than about 5-6 seconds, its going to start heating the cell up and IT WILL DAMAGE IT. Use something large, solder quickly and sink the heat away from the battery by putting a headsink on the top of the battery as soon as you're done soldering to wick the heat away. The damage occurs with prolonged heating.

Just because you don't see damage doesn't mean its not effected by the heat. I've spoken to Bob Simpson on his trials with A123 batteries in his BMW and CR250 projects. He has seen a measurable drop in voltage when soldering (albeit 100ths or 1000ths of a volt, but its multiple thousanths). He has not noticed any issue with cells that were welded... i.e. they measured the same before and after.

 

[tostino]

Just because you don't see damage doesn't mean its not effected by the heat. I've spoken to Bob Simpson on his trials with A123 batteries in his BMW and CR250 projects. He has seen a measurable drop in voltage when soldering (albeit 100ths or 1000ths of a volt, but its multiple thousanths). He has not noticed any issue with cells that were welded... i.e. they measured the same before and after.

Even if it lost a few 1000ths of a volt, it is hardly measurable. I did a discharge test before and after, and it measured within the margin of error of my multimeter. People were telling me i'd lose like 10% of my capacity and maybe even more cell life by doing it. I know I didn't lose anywhere near that much, not even close. With the proper soldering technique, and use of a heatsink, I believe it is possible to solder a pack of lion without any measurable loss of cell life or capacity.

 

[frodus]

i agree, its not anywhere near 10%, maybe more like 0.1% ..... but its there.... thats all i was getting at. Plus, you see no loss in capacity, but what about lifecycle? how many cycles do they have on them? how does one compare soldered vs. welded?

heatsink is a must IMHO

 

[onemintyulep]

On the neg. bottom side you can hear the electrolyte boil, if you overdo it The fat tip - 1/3" - is most important. Then 2 sec. is enough to melt the solder. Do not make it more dramatic than it is! :lol:

 

[tostino]

i agree, its not anywhere near 10%, maybe more like 0.1% ..... but its there.... thats all i was getting at. Plus, you see no loss in capacity, but what about lifecycle? how many cycles do they have on them? how does one compare soldered vs. welded?

heatsink is a must IMHO

30 cycles so far. They were used cells when i got them though.

In the thread i started when i made my pack, fetcher said that my solders may be better than a pack made with inadequate spot welds, because heating during use will not happen with my solders, but with a high amp load, the spot welds can heat up, and that would transfer into the cells. He suggested that over the life of a pack, the one time high heat of soldering may do less to the pack than spot welds heating and making the cells hot.

 

[dscline]

Thanks for the replies! I've determined that silver bearing solder (62% tin 36% lead 2% silver) would be the best choice... it has the lowest melting point of the common solders (179°C), is eutectic, and the silver increases the strength a fair amount. I was going to get a Weller WLC-200, as it appears to be a nice tool I could continue to use. It comes with a nice fat tip, but it's only 80w... do you guys think a cheap 100w iron would be that much better?

 

[johnrobholmes]

Get a nice iron, and the hammerhead tip at the bottom of this page http://www.cheapbatterypacks.com/?sid=1682392&pgid=bldg

The best battery tip ever made. I can tin a cell in about 1/4 second, and solder on a battery bar in 1/2 second.

 

[onemintyulep]

It comes with a nice fat tip, but it's only 80w... do you guys think a cheap 100w iron would be that much better?

It is the MASS of the tip thats important. Massive tips work with less W also. Given there is not much else you can use a cheap 100w soldering iron for - overpowered for electronics... get the neat one with less W.

 

[dscline]

It is the MASS of the tip thats important. Massive tips work with less W also. Given there is not much else you can use a cheap 100w soldering iron for - overpowered for electronics... get the neat one with less W.

Thanks, that's what I was thinking too.

Get a nice iron, and the hammerhead tip at the bottom of this page http://www.cheapbatterypacks.com/?sid=1682392&pgid=bldg

I can see the value in that if soldering batteries end to end, but I intend to do mine in more of a zig-zag... one cell standing up, connecting to another right next to it upside down, with some thin copper strap connecting them. In other words, I'm soldering flat flexible copper strap on the end of a battery at a 90°angle to the battery, such that the strap is flat onto the top of the battery. It seems to me a flat blade tip would be appropriate for that? Or am I misinterpreting the point of the hammerhead?

 

[johnrobholmes]

The hammerhead is designed for end to end, but it has enough mass to make soldering any cell a breeze. I don't do end to end soldering either, but I still use that tip over my fat chisel tips.