[muffildy]

So i went and got myself 32 of the A123 ANR26650 M1A cells, but now i have a problem of how to connect them into a pack. From what i have read, if i were to get them tabbed, the tabbed cells would be current limited to 50 amps depending on the tab used.
http://www.batteryspace.com/A123-Sys...-2500-mAh.aspx
the above link is the website with the stated 50 amp max use for a tabbed cell; they have a link to a 90 amp copper solder bar, but upon emailing to get more info they stated they discontinued it because it was having problems.

That is not the full power of the cell, so the question is how to connect them and get the full 100 or so amps they are capable of?
I saw that one person who used screws to hold the cells together with pressure, and saw that the cells could explode if you didnt allow the pressure relief valve to operate, so that leaves that out.
I was wondering if maybe i put them into a PVC pipe with a compression spring inbetween each cell might work? that way the pressure relief valve wouldnt be 'plugged'. question then is what spring would be suitable of carrying 100+ amps that is also small enough. or maybe you guys have better ideas?

[frodus]

What format of pack are you building, 32 in series? 16 in series, 2 in parallel?

What is this going into?

Springs will give lots of resistance and be severely limited in current delivery.

[muffildy]

32 in series, this is a pack just for testing purposes and will not be used in the final vehicle.

[frodus]

Then just solder some copper bits between them. Don't keep the iron on it too long, and make sure the iron is SUPER hot. Melt some solder on, touch it to the tabs, let it flow, then remove.

[muffildy]

that wont damage the battery? i thought soldering was very bad for those cells. Or do you mean melt solder onto the copper tab and then squish it onto the battery?

[frodus]

I mean, solder copper tabs to the actual cell itself.

Too much Heat hurts the cycle life of the battery, but do you care for a test pack?

Just keep the iron hot so it flows the solder quickly, solder it, remove heat, and use a fan to cool it off.

If you use a "medium" heat iron, it'll take too long to flow the solder, and it very well could damage it.

Guys on endless-sphere (electric bicycle forum) do it all the time. You should go over there and get some ideas.

[muffildy]

i was hoping to avoid damaging the cells, after the experiments were over with i was going to tab them and use them as replacement cells in power tools battery packs.

[frodus]

Well, why'd you ask how to put them together?.... you already knew the answer I was going to give.

If you follow my directions, you won't harm them. Bike guys do it all the time. Just don't keep the iron on there for long, and use a HOT tip for a short period and actively cool it off with a high cfm fan blowing at it after you're done.

Unless you have money to shell out for a decent battery tab welder, soldering is about the only option. Putting them together with pressure is a really bad idea, it blocks the vents.

I've built quite a few 26650 packs with A123 and K2.... we haven't damaged any noticeably. Get in, Get out, Cool it down quickly.

[muffildy]

i was hoping for different options than that one.
the battery tab welder will still be limiting the battery current to 50 amps according to the website i linked.

soldering them is something i would only consider as a last resort because i dont want to damage the cells.

you say springs i will lose too much current, so what other options are there than springs that will not prevent the cell from venting?