# why build packs with individual pouch cells?



## dougingraham (Jul 26, 2011)

scott said:


> why build packs with individual pouch cells? from what i read, calbs are made with similar material.


Similar is not the same. The A123 pouch cells are 20AH and can do a 18C continuous discharge. If you parallel 3 of them to make a 60AH equivalent to a 60AH CALB the difference is the CALB can do 3C continuous or 180amps while the A123 arrangement can do 1080 amps continuous. If all you need is 180 amps this is no big deal. If you need 1080 amps continuous then it is. (note: A123 does not say what the continuous discharge rating is on the datasheet. I extrapolated the 18C number from the power rating/nominal voltage /ah)

For a street car used as a daily driver there is little need to use pouch cells. The prismatics are better for normal use. If you are racing then there is a good reason to use pouch cells. The mass of a usable battery pack goes down and the the mass of the vehicle goes down.


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## scott (Feb 15, 2009)

thank you for the answer. So, for comparision, its like racing fuel to premium gasoline. right


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## Duncan (Dec 8, 2008)

scott said:


> thank you for the answer. So, for comparision, its like racing fuel to premium gasoline. right


No - its more like the difference between rocket fuel and coal


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## scott (Feb 15, 2009)

so, does this mean the amp hour rating of pouch cells are under rated? and that you can get more range from pouch cells?


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## onegreenev (May 18, 2012)

Not really. An Ah is an Ah pouch or not. The pouch cells are designed to allow you to discharge them faster. In other words I can use that ah faster in the pouch cell. The best I ever had my prismatic cells give me was 7C. A123 cells are rated actually for 20C. A 100ah prismatic cell could very well do 12c or 1200 amps with the new Calb cells. With the A123 cells if you built a 100ah cell you could get 20C or 2000 amps. Which do you want for the race track. With 200ah cells your looking at 4000 amps. So a nice string of A123 pouch cells built up into a nice pack you could really do well on the track. There are however other types of lithium cells that can do even better but they are not LiFePO4 cells. We like LiFePO4 Cells. The best to date prismatic cells you can buy are the Calb Grey cells.


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## dougingraham (Jul 26, 2011)

scott said:


> so, does this mean the amp hour rating of pouch cells are under rated? and that you can get more range from pouch cells?


It means you can make a smaller and lighter pack with the pouch cells that will deliver the power (max current with less voltage sag). But it will have less stored energy so less range. (Smaller bucket but with a bigger hose so you can drain it faster).

But unless you are racing you generally want a large enough pack to get your range that you get the power level anyway.

A drag racer only needs to go 1/2 mile (1/4 mile down and back). If they get 1000wh/mile (which would be terrible) they only would need a 0.5kwh pack. But that pack would need to be able to dump half of its energy in less than 10 seconds. This means 180C would be the desired cell rating. A 20AH cell would have to be able to do 3600 amps. This does not exist so they need a larger pack than 0.5kwh.


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## IamIan (Mar 29, 2009)

dougingraham said:


> If they get 1000wh/mile (which would be terrible) they only would need a 0.5kwh pack


It's even worse than that. (see bellow)



dougingraham said:


> This does not exist so they need a larger pack than 0.5kwh.


Just a real world Racing BEV for comparison of that concept.

White Zombie
Gets 0-60 in ~1.8 Seconds:
Which ( simplified ) requires an average of ~231kw of power at the wheel for those ~1.8 Seconds. If we assume ~80% efficiency from battery to wheel that's about ~289kw (~400HP) @ battery. This would only be ~0.145 kwh of battery energy used over those ~1.8 Seconds.

(Simplified) In those ~1.8 seconds they will only travel about ~79.2 Feet. To get that 0-60 in ~1.8Seconds, they are using about ~9,666 Wh per mile. 

No battery I know of (at any cost) can discharge in ~1.8 seconds ( ~2000C ) to only be that ~0.145 kwh sized battery. So the White Zombie uses a larger ~22.7 kwh rated battery pack ( of Dow Kokam lithium polymer cells ). Which is only discharging at an easier ~12.7C to still give him that ~289kw of racing battery power he wants.

The minimum A123 (20Ah) Pouch cell pack that could give that same ~289kw, would be ~193 cells. would still be a ~12.5 kwh battery pack. They are rated for up to a max pulse of ~1.5kw each @~90%SoC. That would be a discharge pulse rate of ~23C.


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