# Difference in A123 20Ah USA vs Korean cells



## Batterypoweredtoad (Feb 5, 2008)

Are they the same age and amount of usage?


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## rwaudio (May 22, 2008)

Batterypoweredtoad said:


> Are they the same age and amount of usage?


They are brand new and have one complete cycle for testing capacity/IR.
Actual age, who knows, I've had the Korean cells about 8 months longer if that helps.


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## Batterypoweredtoad (Feb 5, 2008)

Sorry, I don't really have any knowledge of batteries that can help. I just asked about the age because of the mention of the cells "breaking in" and gaining capacity after a few cycles in another members build thread. I believe it was his battery he used to power the pl6 for testing. When he broke that battery down into individual cells they showed a larger capacity than they did in unused condition.


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## CroDriver (Jan 8, 2009)

How much capacity where you able to get and at which current? We usually get about 18-19Ah out of them.

Btw. You shouldn't discharge them to 2,2V. I would recommend not to go below 2,8V. We have seen damaged cells after a few cycles down to 2,5V.


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## marc02228 (Jan 15, 2011)

CroDriver said:


> How much capacity where you able to get and at which current? We usually get about 18-19Ah out of them.
> 
> Btw. You shouldn't discharge them to 2,2V. I would recommend not to go below 2,8V. We have seen damaged cells after a few cycles down to 2,5V.


Which capacity do you mean? I've some of the USA Cells...
1	18563
2	18377
3	18243
4	18380
5	18093
6	18010
7	18660
8	18390
25	18807
26	18754
27	18621
28	18608
29	18290
30	18601
31	18512
32	17811
33	18849
34	18709
35	18653
36	18637
37	17740
38	17701
39	18260
40	18206
41	17802
42	18267
43	17943
44	18791
45	18437
46	18585
47	18378
48	18425
49	18486
50	17967
51	18391
52	18524
53	18324
54	17678
55	18119
56	18838
57	18003
58	18022
59	17999
60	17430
61	17870
62	17865
63	17647
64	17874
65	18511
66	18373
67	18533
68	18926
69	18893
70	18969
71	18827
72	18655
73	18532
74	18751
75	18723
76	18651
77	18656
78	18824
79	18439
80	18332
81	18332
82	18133
83	18136
84	18438
85	18683
86	18574
87	18472
88	18385

249	18819
250	18737
251	18510
252	18739
253	18145
254	17899
255	18039
256	18011
257	17953
258	18299
259	17989
260	18185
261	18225
262	18144
263	18402
264	18320

Discharge @ 38A from 3,65 to 2,25V

a couple of minutes after discharge is done (disconnected load), they are up to ~3,1 V again.

do you think one should put in a bit of charge for storing them after the discharge?


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## rwaudio (May 22, 2008)

CroDriver said:


> How much capacity where you able to get and at which current? We usually get about 18-19Ah out of them.
> 
> Btw. You shouldn't discharge them to 2,2V. I would recommend not to go below 2,8V. We have seen damaged cells after a few cycles down to 2,5V.


Hey Mate,

The testing preset that a few people are using on the PL6 is for a single cell at 38A charge to 3.65v with a C/20 termination then a 38A (~2C based on actual capacity) constant current discharge to 2.25v. As mentioned above the cells recover to 3.0 - 3.1v after discharge.
My average with Korean cells was 18.66Ah and 18.55Ah with USA cells.

The purpose is to make each 3P (or whatever parallel number you are using) grouping the same total capacity. I have an 8S3P module that runs the chargers and although it's top balanced they all hit the bottom about the same time.

In real use I probably won't take my cells past 80% DOD, and my daily commute will be around 25% each way with the opportunity to charge at work.

Mate, I'm sure you are using real A123 cells, have you noticed a difference between cells from different sources?


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## CroDriver (Jan 8, 2009)

marc02228 said:


> Which capacity do you mean?


Overall capacity of random cells. Basically what you have posted...



marc02228 said:


> 1 18563
> 2 18377
> 3 18243
> 4 18380
> ...


So your average is 18,355 Ah @ 100% DOD. 

You should keep the cells charged while stored for a longer time. A discharged cell will get damaged over time.



rwaudio said:


> Hey Mate,
> 
> The testing preset that a few people are using on the PL6 is for a single cell at 38A charge to 3.65v with a C/20 termination then a 38A (~2C based on actual capacity) constant current discharge to 2.25v. As mentioned above the cells recover to 3.0 - 3.1v after discharge.
> My average with Korean cells was 18.66Ah and 18.55Ah with USA cells.
> ...


That's a good approach but I wouldn't be too confident in the test results. How do you clamp the cells to the battery tester? What kind of tester do you use?

The resistance between the tabs and wires can result in more capacity difference than actual cell differences. Try to test the same cell several times, but disconnect and re-connect it after each cycle.

Unfortunatley I can't tell you much about what we're doing or using. That doesn't mean that I can't help with our experience. 

Btw. Make sure that sufficient pressure is applied to the cells during the tests. This is very important.


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## marc02228 (Jan 15, 2011)

CroDriver said:


> Overall capacity of random cells. Basically what you have posted...
> 
> 
> 
> ...


As rwaudio wrote, we are using the Powerlab 6 from Revelectrix to measure the cells. I attached a picture of the way, I'm connecting the charger to the cells.

Thanks for the advice to put some pressure on the cells. What's different, when pressure is put on the cells? 
I noticed, that some cells (3-4 til now) are a bit softer after discharge.


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## rwaudio (May 22, 2008)

CroDriver said:


> That's a good approach but I wouldn't be too confident in the test results. How do you clamp the cells to the battery tester? What kind of tester do you use?


I'm using the same clamping system for charging that I use to assemble the cells into a pack. I did try other simpler/faster connection methods but they all resulted in significant heat in the connection.

I'm using the PL6's, the same as marc02228 posted above. They are of course hobby grade, but the results seem pretty consistent in the testing that I've done. I wouldn't call the results absolute, but relative and repeatable accuracy seems pretty good.

I built my first packs out of random cells and they didn't perform very well at one end or the other due to capacity differences. Using this method, although not perfect does make a drastic difference in how the cells behave at the bottom when top balanced for example, I can also weed out cells with low capacity or high IR.



CroDriver said:


> Btw. Make sure that sufficient pressure is applied to the cells during the tests. This is very important.


I've heard this before, and I don't think that many of us using the A123 cells are doing this. Can you elaborate on what happens in the cells and why this is important, as well as how much pressure we should be trying to achieve?


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## Zak650 (Sep 20, 2008)

In cycling through my cells I put them between two 1/8" aluminum plates with about a 4 lb block on top of them. I observe that they tend to get flatter but not necessarily thinner after cycling through a charge up and drain down and then back up to a storage voltage.


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