# A123 Pouch Cell Summary



## Jordysport (Mar 22, 2009)

Hi Guys, Firstly like to thank all on this forum for their help on my project, now i've been looking at the A123 Pouch cells and there has been information scattered everywhere and sometimes not listed at all. 

1) Sourcing A123 Pouch Cells 
Seems that alot of the A123 Cells MAY be fakes or back door supplies but facts and rumours are different things. Now As they can't be bought direct by DIY'ers. Is there any favourite suppliers of these cells? 

Victpower? Lots of good but just as many bad. Quality of cells, dud cell %. 

2) Secondly: Packaging, we can't have a perfect cell and these are no exception and packaging into a pack is difficult as they are so flimsy & fragile. There are some good ideas out there but as tried on EVTV the cells expand and contract on cycling, and have exploded the resin they were moulded in, (Don't know why they tried it multiple times with resin) but what should be allowed for expansion. 

Eg. see my design I knocked up, I haven't put in an insulating block inbetween cells yet but will be done. I was thinking of putting a moulded foam around the modules to allow for expansion and contraction, but what should be allowed for 5mm, 10mm, 50mm!! I am limited on space but they need to last. (70V 60Ah Pack)


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## MalcolmB (Jun 10, 2008)

rwaudio has done a lot of work with these cells. See post number 4 here for some useful information on tab connections: http://www.diyelectriccar.com/forums/showthread.php?p=311271#post311271


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## Jordysport (Mar 22, 2009)

MalcolmB said:


> rwaudio has done a lot of work with these cells. See post number 4 here for some useful information on tab connections: http://www.diyelectriccar.com/forums/showthread.php?p=311271#post311271


Yes the Half moon approach looks good in theory but he found it was unreliable: 
http://www.diyelectriccar.com/forum...-cells-testing-connection-method-64067p5.html
Post #42


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## rwaudio (May 22, 2008)

MalcolmB said:


> rwaudio has done a lot of work with these cells. See post number 4 here for some useful information on tab connections: http://www.diyelectriccar.com/forums/showthread.php?p=311271#post311271


The half moon is actually the bad connection in this comparison, whatever mechanical method is used what the results show is that direct overlapping of alternate tabs is the best low resistance connection.



Jordysport said:


> Yes the Half moon approach looks good in theory but he found it was unreliable:
> http://www.diyelectriccar.com/forum...-cells-testing-connection-method-64067p5.html
> Post #42


The method shown in post #42 is what I'm using in my car right now with good results, (however I think it could be improved upon) if I had the normal full tab cells I would go with alternating tabs and a simple solid mechanical clamping. 

In short if I were to do it again I would *not* go with the method I'm currently using which is basically the same as Jack R's method with a single conducting spacer block with clamps on either side.


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## Jordysport (Mar 22, 2009)

rwaudio said:


> The half moon is actually the bad connection in this comparison, whatever mechanical method is used what the results show is that direct overlapping of alternate tabs is the best low resistance connection.
> 
> The method shown in post #42 is what I'm using in my car right now with good results, (however I think it could be improved upon) if I had the normal full tab cells I would go with alternating tabs and a simple solid mechanical clamping.
> 
> In short if I were to do it again I would *not* go with the method I'm currently using which is basically the same as Jack R's method with a single conducting spacer block with clamps on either side.


Ok, so the method in my design (v similar to Jack R's) is good but can be improved on. these will be full length tabs, what do you mean by "alternating tabs" mine is a 21S3P Pack as shown in Post#1 to produce a 70V 60Ah pack just to clarify & Total mass of 32.5Kg


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## rwaudio (May 22, 2008)

Jordysport said:


> Ok, so the method in my design (v similar to Jack R's) is good but can be improved on. these will be full length tabs, what do you mean by "alternating tabs" mine is a 21S3P Pack as shown in Post#1 to produce a 70V 60Ah pack just to clarify & Total mass of 32.5Kg


That is correct, what I'm using now is basically the same as what you have in the rendering and it does work well. However I know it can be improved, attached is an expanded view of what I'm talking about. (obviously not to scale)










copper bar
group1 cell 1 +
group2 cell 1 -
group1 cell 2 +
group2 cell 2 - 
group1 cell 3 +
group2 cell 3 -
copper bar

group1 is a parallel cell group to be connected in series with group2, this would work equally well for 2P and greater up to the point the tabs are not long enough for this to be practical. 

The surface area of the overlap and the clamping force should be as high as practical for the number of cells being used.

The bolts (I would recommend 2 bolts per tab clamp) should go through the tabs (punched holes) and not on the sides of the of the tab.


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## Zak650 (Sep 20, 2008)

rwaudio,

That's very similar to what I'm doing, you might try these changes:

1)bend a very small S curve into the middle cell of your group of 3 on each side just above the top of the cell. This will allow this cell to rise vertically.
2)make the size of the lower clamping bar be 8mm thick, 14mm at the top and taper to 10mm at the bottom 
3)drill and tap for 6mm x 1.0 thread on 15.9mm(5/8") center to center. This allows for use of standard 1/0 awg short series two hole lugs on the top for the first and last cells of the battery, same spacing for group joints
4)bolt the six cells together 3 on a side flat on a table all (+) tabs together obviously, VERY DANGEROUS if mixed up
5)pick the clamps straight up, squeeze the cells together tight
6)16mm width and S curve bend can be adjusted to make bottoms line up
7)you now have one 6P group with 2 hole clamping per pole at the top

Zak


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## Jordysport (Mar 22, 2009)

On this one the terminals are not overlapping as there is not physically enough tab length (26.09mm) so had to lay 3 flat on the copper joiner and two bolts through and same for the other side. (gives a 67V 60Ah pack)


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## rwaudio (May 22, 2008)

Zak650 said:


> rwaudio,
> 
> That's very similar to what I'm doing, you might try these changes:
> 
> ...


My cells won't work in this configuration I'm just sharing the design, however I do think your comment about the bolt spacing to directly attach the 2 lug ring terminals is a very good addition. The actual mechanics will depend on the number of parallel cells but if the basic idea is used as a guide it's the lowest resistance connection that I've found and andre ferron confirmed in high current testing.



Jordysport said:


> On this one the terminals are not overlapping as there is not physically enough tab length (26.09mm) so had to lay 3 flat on the copper joiner and two bolts through and same for the other side. (gives a 67V 60Ah pack)


Do you have the cells on hand yet? If you do you will see that the insulated area where the tabs come out can easily be bent to bring the tabs closer together to allow at least a 3P configuration to work, maybe even 4P.

The 90degree bends were simply used to clearly show the alternating tab stacking which is the key to the low resistance connection. As Zak650 mentioned these can be fairly tight S curves to get the tabs and cells in the right place.


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## dougingraham (Jul 26, 2011)

Jordysport said:


> There are some good ideas out there but as tried on EVTV the cells expand and contract on cycling, and have exploded the resin they were moulded in, (Don't know why they tried it multiple times with resin) but what should be allowed for expansion.


They don't actually swell and contract during normal operation. They puff never to recover if they are overcharged or if you exceed some terribly high discharge rate. In the EVTV case it has usually been overcharging that is the culprit. (Manual charging and walk away to talk on the phone kind of thing.) One of the cases was probably caused by a faulty cell.

If they are swelling in any measurable way then they are ruined.


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## MalcolmB (Jun 10, 2008)

dougingraham said:


> They don't actually swell and contract during normal operation.


I'd go along with that. The cylindrical cells, including those from A123, don't allow any significant swelling, otherwise the case would rupture. I've dissected a couple of cylindrical Lifebatt cells, and there's no space for expansion inside. The "jelly roll" completely fills the casing. All they have is a small vent on the end cap to allow the electrolyte to boil off in case of overcharging/overheating.

EDIT:
Having said that, I do remember CroDriver saying that these cells must be clamped together and he has plenty of experience with them. Has anyone monitored pouch cell thickness during a typical charge/discharge cycle?


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## js1tr3 (Aug 8, 2012)

40 micron expansion, during normal cycling at 1 C rate.
http://www.formula-hybrid.org/wp-content/uploads/A123_AMP20_battery_Design_guide.pdf
http://www.formula-hybrid.org/wp-content/uploads/A123-Pack-Design-Guide-for-Cylindrical-Cells.pdf


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