Soldering battery pack for the first time....need advice

[KevinL]

....and at least I got the first part right: order your cells with tabs!!

I just need to know the answer to what is probably a freaking dumb question. As you know, the tabs will create some space in between the cells. I'm soldering a straight stick of 4 to jam into a Maglite.

Should I make the tabs form a "S" shape or a "W" shape when I put them together?





The question being, when I push the cells together, the tabs will flatten out and perhaps stick out beyond the cell diameter.

Or have I gotten it all wrong?

Any other tips are most welcome. Thanks

[CKOD]

Trim the tabs so they wont stick out when you flatten it And I'd go for a "S" configuration, as the "W" would have low strength. Simply tugging in opposite directions would peel the connection apart, in a manner the solder joint is weakest. Try and make sure your joint between the 2 tabs is as flat as possible, so it uses the minimum amount of solder. Some hemostats, or something to pinch the tabs together would be nice. A paperclip would be ideal, but they are ususal nickel plated and would get solded in too.

[hank]

Press down flat on a soldering pad
http://www.google.com/search?q=soldering+pad
to avoid getting a lumpy connection.

Dang battery pack plastic cases, at least the ones I've tried to refill, have almost no extra space, they assume spot-welded strings of batteries.

[kaptain_zero]

For end to end soldering of cells, I would have suggested using an 80w soldering iron with a hammer head tip and skip the tabs as they are meant for side by side cells.

Go to YouTube, and search for a video called "Making custom battery packs", it shows how to go about doing this work efficiently and with a minimum of heating of the cells. The trick is using a hammer head tip and a full 80 watts of soldering power.... you need a hot iron with lots of reserve to heat quickly without transferring too much heat to the internals of the battery cells.

Well... that's the way I would do it at least.......

Regards

Christian

[Mr Happy]

I haven't done this, but I would stick the tabs flat out the side of the cells so they are not folded, and then after soldering I would fold the pair of joined tabs down along the outside of one of the cells. Of course, this requires a bit of extra space available on the outside of the cells.

[kaptain_zero]

Don't forget the possibility of shorting out those tabs against the side of the cell depending on which way it is bent and the fact that you would have to cover the tabs with insulation/shrink wrap so it can't short against the inside of the light barrel OR against the side of one of the cells. 4 LiIon cells with one or more being shorted out inside a Mag Light would make a nifty pipe bomb only without knowing when it's going to go off.

If it were me, I'd either carefully remove the tabs and gently sand the tops and bottoms, just to clean them and remove any nibs left from the tab welds and then solder them together properly as shown in the video I suggested above, but perhaps more safer is to simply order a new set of cells and get the hammer head tip and soldering iron and do it right..... It's not worth risking life and limb for such a small investment of 4 batteries.

Regards,

Christian

[Mr Happy]

Don't forget the possibility of shorting out those tabs against the side of the cell depending on which way it is bent and the fact that you would have to cover the tabs with insulation/shrink wrap so it can't short against the inside of the light barrel OR against the side of one of the cells.

I agree with this. It would be important to fold the tabs in the direction where the tabs have the same potential as the cell casing. Also, I think a constructed pack should always have an outer layer of shrink wrap to keep the whole pack securely together.

There is also a question of how to take balancing taps from the cell joins and bring them out somewhere safely. For a Mag application, surely the usual solution is just to install the cells loose so they can be recharged externally in a balancing charge setup? IMHO an assembled pack is only needed where some kind of integrated charging solution is part of the system.

[HarryN]

I would use a lead based solder paste so that it melts in easily, rather than attempt with solder wire. Then again, I have virtually abandon wire solder completely.

[Mr Happy]

I watched the YouTube video referenced above, but be aware, the demonstration was using Nickel cells that were "designed for soldering". The amount of heat being applied to the cells by the iron there is dangerous, and can damage or destroy cells that were not designed for that treatment (for example, lithium ion cells). Even consumer nickel cells can fail -- when I once applied much less heat than that to a consumer NiMH cell it suffered an internal short and melted down with heat and smoke.

Also, note again that nickel cells can be assembled into series packs for charging without balancing taps. Lithium ion cells cannot. Do not apply the techniques in the video to lithium ion cells. That is why the cells were supplied with tabs.

[CKOD]

I watched the YouTube video referenced above, but be aware, the demonstration was using Nickel cells that were "designed for soldering". The amount of heat being applied to the cells by the iron there is dangerous, and can damage or destroy cells that were not designed for that treatment (for example, lithium ion cells). Even consumer nickel cells can fail -- when I once applied much less heat than that to a consumer NiMH cell it suffered an internal short and melted down with heat and smoke.

Also, note again that nickel cells can be assembled into series packs for charging without balancing taps. Lithium ion cells cannot. Do not apply the techniques in the video to lithium ion cells. That is why the cells were supplied with tabs.

+1 on not soldering cells that specifically say in the datasheet DO NOT SOLDER.
And just because the RC community successfully does it, doesn't mean you should do it. There is so many puffed up Li-po's venting/flaming batteries and other general abuse, and ignorance of proper electronics, its a miracle that more of them dont burn down their shed/garages. I'd hate to paint with a wide brush like that, but anytime you get a LARGE community like that the idiots come out to play.

A professional pack made from canned cells will *never* be soldered directly to the cells, and soldering by applying heat, and then mashing the molten surfaces together and hoping for the best is a horrible way to get consistent joints, regardless of any anecdote.

Trim the tabs so nothing will hang out of the finished joint, and then have them positioned for soldering, solder the tabs together, and then push the cells into the proper close stack after the joint cools. Its not impossible to do, Ive welded stick type packs with a pedal operated spot welded head, and took a little bit of thinking and maneuvering before I started actually welding. Much more bulky then any soldering iron, so you should have it easy. Just make sure you get a good joint that flows properly, use flux, and pre-tin the portion of the tab you're soldering together to make sure it wets properly.

[KevinL]

+1 on not soldering cells that specifically say in the datasheet DO NOT SOLDER.
And just because the RC community successfully does it, doesn't mean you should do it. There is so many puffed up Li-po's venting/flaming batteries and other general abuse, and ignorance of proper electronics, its a miracle that more of them dont burn down their shed/garages. I'd hate to paint with a wide brush like that, but anytime you get a LARGE community like that the idiots come out to play.

A professional pack made from canned cells will *never* be soldered directly to the cells, and soldering by applying heat, and then mashing the molten surfaces together and hoping for the best is a horrible way to get consistent joints, regardless of any anecdote.

Trim the tabs so nothing will hang out of the finished joint, and then have them positioned for soldering, solder the tabs together, and then push the cells into the proper close stack after the joint cools. Its not impossible to do, Ive welded stick type packs with a pedal operated spot welded head, and took a little bit of thinking and maneuvering before I started actually welding. Much more bulky then any soldering iron, so you should have it easy. Just make sure you get a good joint that flows properly, use flux, and pre-tin the portion of the tab you're soldering together to make sure it wets properly.

Thanks yours has been the best advice so far.

I do not solder cells directly together, period. Whoever wants to do so can do so, but it's not going to happen on my watch. Besides, my cells were tabbed for me. Why make my own life harder anyway