Received Pouch Cells From A123rc

[Electricdirtbiker]

There has been a lot of concerns about ordering pouch cells from A123rc, and what your might receive.
I just received my cells this morning, 6 business days after order placed, with the free postage selection.
I don't have a picture.
The cells are all full tabbed, tabs are slightly bent, but appare unused. The 20ah cells (8) all measured ~3.28v.
Not knowing their age, 3.28v is a little on the high side for idle cells. They may have been charged and sorted.
My equipment can perform only a few amp hour load testing, I will report any thing odd.
The cells have a slight bow near the tabs, as well as across the entire cell. So unless I get brave and flatten them,
I will never be able to package them as flat as ideal. Any ideas?
The cells are all labeled "made in usa".
The cells appare new, accept for some small scuff marks here and there.
The a123 shipping trays are not new and a little dirty. Some manual handling before shipping I think.

Electricdirtbiker

 

[mvly]

A picture is worth a thousand words.

Any photos of these cells?

 

[miro13car]

my view - they are factory rejects, obtained from recycler, it all make sense, plastic trays are dirty, new QC passed A123 are ideally stright not a slight bent.
All point of using A123 prismatic other than fantastic electric characteristics is that they are flat in battery pack.
Anybody any other opinion?
I don't know but tose cells are very attractive for my application, even more that their operating temp. is specs to minus 30C !!! Especially attractive for Canada,
I was very close to ordering 15Ah ones, but now?

 

[agniusm]

As mentioned here lots of times, if they perform and the capacity is on the 20 side, prob. there is nothing better, even if they are rejects. I got mine and most of them were dead so you are lucky Good luck with the pack

 

[bigmoose]

Could you do me a favor on the tabs?

Confirm that they are 4.5cm wide by 2.6cm long?
Can you measure the thickness of each?
Can you tell the material of each tab?

Sincere thanks!

 

[Electricdirtbiker]

Bigmoose, the tab sizes are as you described. The neg tab is .007" thick, copper with maybe nickle plating. The pos tab is all nickle color, don't know what material it is. Will solder stick?
These cells do sound like a hit or miss gamble. If they hold up through bench testing, I'll install then on my bike for real life testing.
Thanks for the feed back.
Elecrticdirtbiker

 

[liveforphysics]

Negative tab is tinned copper.

Positive tab is annealed aluminum.

They commonly ship slightly tweaked. Every pouch cell mfg I've ever seen, (and I've seen them all over China and Korea etc), uses human hands to clip the cells into the formation charge machine's clips. This commonly results in little bends and creases.
If your pouches themselves are bent, you have nothing to fear from pressing them out flat. Put them between a couple of books and stand on the top book.

 

[Electricdirtbiker]

I will try to flatten the cells that way.
I see examples of soldering and bolting to the tabs. Using a hot iron will rosin core solder stick to the annealed aluminum?
Thanks

 

[johnrobholmes]

You will need an aluminum specific solder, they are zinc based and have special flux.

 

[agniusm]

Would it not be better to use some sort of clamping instead of soldering. This way it will be easy to replace a cell and you will get neater results??? http://e-motion.lt/bbpress/topic/12/page/5

 

[bigmoose]

I have been studying ultrasonic welding for the tabs. It looks like it would work, but it appears impossible to manipulate a stack of cells at all, yet alone safely by the weld head and anvil. I think I am seeing why when A123 built the stack they used laser welding. It is looking like mechanical terminations is the only approach for small volume fabrication.

 

[TylerDurden]

I noodled around on a modular prismatic pack design, while commenting in Chris Jones' build thread.

This version uses plastic (or fiberglass) rails to clamp the tabs and copper straps. The clamping bolts would be insulated from the tabs.


Please forgive the amateurish CAD.

 

[jonescg]

BigMoose - the other thing to remember is that most A123 EVs are cars, and they can stack them vertically so any kind of clamping system is going to be much easier. On an e-moto, space is at an absolute premium, and it's likely to be enduring more vibrations and g-forces. So a termination system that is space efficient and robust, and is good for horizontal stacking needs to be developed.

It's even harder on the Turnigy cells cause the little shits are so much smaller and fiddly. A friend of mine keeps saying I should spot-weld them, but I can't see how you can even fit the jaws of a spot welder in place to make it happen.

 

[docnjoj]

Please forgive the amateurish CAD.

That looks like pretty professional work to me, Tyler! I really do wish there was an easier way to do the terminal work on those A123's, though. Each assembly is an engineering nightmare, at least to my soldering skills. I solder much better than I can make CAD/Cam!
otherDoc

 

[bigmoose]

Jonsey, I talked to the manufacturer and this Amtech Ultraweld 20 will ultrasonic weld the tabs. Here is a used one up for sale just for info, something around $12K US, but that is professionally refurbished. Two just sold on eBay 5 days ago for around 3K for both of them!
http://www.usedultrasonicwelders.com/MetalWelders20.htm#
If I were going to weld the tabs, first choice would be Nd:YAG laser, followed by ultrasonic, but the price of entry is sure steep!
When the link goes dead, here is what this machine looks like:
View attachment 2
Here is what the weld looks like with this machine:

 

[amberwolf]

After some thought and various pics around the web and ES of cells and terminations, I think that what I seem to recall was the EIG NMC pouches appear to have the best easily-stackable method. I am not totally sure how they work, and I cannot now find any of the pictures I have seen over the last months that were labelled as of those types, just one that I think might be, so I might be mixing up different manufacturer's methods into a mishmash that might nto actually work. :? Lots of the pics were very low resolution so I am not certain of details, just guessing based on stuff I do know about various ways things are commonly put together.

The only person on here that I'm sure could verify this is Jay64, as he actually has some of these cells, presumably including the hardware I think I am remembering.


Basically, I think there are short brass (?) plates welded by some method to the actual cell tabs. These plates are 90-degree bends, with two holes in the part perpendicular to the cell itself. I can't find the pic of the cells that looked like this now, but I thougth it was on ES in one of the A123 threads. Might be a "lost image" after the problems this summer.


The cells lay flat in trays (plastic?) with the bent plates down over a set of what must be molded-in threaded "nutserts" in the end of the tray. (couldn't see the actual trays or nutserts in the pics, but it's the only way I can imagine it workable).

There are alignment holes in all the trays so they can be easily stacked and bolted together thru the corners or edges (not totally sure about this, but it would make sense).

Once your series cells are all stacked up, angled bussbars are bolted thru the plates on the tabs into the trays. Angled so that they connect the + of one cell to the - of the next without flip-flopping every other cell. I'm not sure how easy this would be to do without potential shorts on the cells, but I saved an enlarged version of part of a pic of a pack that shows what I think is this method:


Anyway, if you don't have room for a wide stack of cells you could bolt a plate across several stacks of these things and tthen bolt cables or busbars between each stack for series connections.

Paralleling them is easy, as you just use busbars across all the negs and other busbars across all the positives, and can even just use extra-wide ones to bolt across sets of them to create extra pack stiffness.

Because the trays are doing all the supporting, there should be no stress on the tabs at all, unlike some of the other methods I've seen proposed that would require a box be built around the pouches that supports them as a group, that is then bolted to all the cell interconnect hardware.

The only real problem I see with the whole idea is that I can only imagine injection-molding as the way to make the trays including nutserts/etc., and that is probably going to be pretty expensive per-tray unless someone does it as a venture to sell them to all those people with the A123 pouches.

Hopefully this all makes sense without a drawing, but I can try to sketch one up if it doesn't.