# Recent Battery Test (Kokam)



## DIYguy (Sep 18, 2008)

Interesting. Thanks for posting. out of curiosity, which cell is the replacement ( #13 perhaps?) and did you spend any time on balancing?

As I recall, this pack was given up for dead, so. . your ability to use it for several years demonstrates the common belief in the quality of the Kokam cells.


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## major (Apr 4, 2008)

DIYguy said:


> Interesting. Thanks for posting. out of curiosity, which cell is the replacement ( #13 perhaps?) and did you spend any time on balancing?


I really didn't pay much attention to the cell #s and try to reassemble in the same order. The bad cell was about 4th from one end in the old package, don't recall if it was + or -. Negative, I think. I think I can find where the replacement cell is in the rebuild as it had some different color tape on it. CellLoggers always use most negative cell as #1. I wasn't too careful about cell I.D. for this test. I just wanted to see if the damn thing was worth fooling with 

Also that is the reason I didn't balance closely or bring all uniformly up to 4.2 V/c which I'd do for a legit capacity test. In use I simply monitor the cells and manually balance when one gets outa wack. To me that means like 60 mV high or low. I just go into it with an external resistor or power supply and make it even. Had to do it like twice to a couple of cells over the year or two since I built it. But I don't use it that much and don't deep discharge it (except when testing). 

From memory, these cells came back a lot closer after recharge. I left the CellLoggers run during the charge. If I get a chance I'll see if I can post a graph of the charge.

I am not advocating running Lithium batteries with or without BMS. I don't even want to go there  This is simply the way I personally use an experimental battery and I have been experimenting with batteries for a few decades. 

major


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## charliehorse55 (Sep 23, 2011)

Does anyone know what the rough cost per kWh of Kokam cells is?


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## major (Apr 4, 2008)

major said:


> From memory, these cells came back a lot closer after recharge. I left the CellLoggers run during the charge. If I get a chance I'll see if I can post a graph of the charge.


Here is the entire log from the CellLoggers.










From about 2000 to 4000 seconds, a top off charge with power supply at about 6 Amps.

From about 8000 to 10000 seconds, discharge test at 80A as shown in post #1.

From about 12,000 to 17,000 seconds, charge from bulk charger at 17.5 amps.


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## major (Apr 4, 2008)

O.K. So I charged and top balanced all 14 cells to 4.2 V/c within about 30 mV. Then I ran a 2C discharge. But somehow lost the data from one of the cellLoggers (cells 8 - 14) (positive half of the battery). But here is the graph I can get.










So it appears that cells 1 & 3 have a higher internal resistance or reduced capacity.

BTW, cell 13 was the replacement cell.

major


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## Yabert (Feb 7, 2010)

Interesting data... and pictures of cell connection.
Do you have some pictures of how the cells pouch are maintained.

Thanks


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## major (Apr 4, 2008)

Yabert said:


> Interesting data... and pictures of cell connection.
> Do you have some pictures of how the cells pouch are maintained.


Ref: http://www.diyelectriccar.com/forums/showthread.php/lithium-battery-monitor-39708p2.html The attached photo in post #16 shows the battery. Cells are separated by aluminum plates. Here attached is another pic. You can see the side of the battery on the right.


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## Yabert (Feb 7, 2010)

Nice! Thanks to share.


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## major (Apr 4, 2008)

I got into a battery test mood or mode, so........ I had built 3 of these 14 cell 40Ah batteries. Two stayed in the lab. One had been used for bench testing other stuff as a DC power supply. One just sat by the window. Remarkable how little self discharge it had and one CellLogger (on 7 cells) showed only a 3 mV delta V after over a year. And all 14 cells were above or near 4 V/c. Anyway, here are the 2C discharge curves on those two and a charge curve for the one I tested yesterday.


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## major (Apr 4, 2008)

Here's what got me started. The bad cell. All puffed up.


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## steven4601 (Nov 11, 2010)

Major,

Are those packs ex- Victors audi ev batteries ?


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## major (Apr 4, 2008)

No, but of that design originally.


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## Ertike (Mar 21, 2012)

You say you have been playing around with batteries for decades, have you heard anything about this new technology Silicone batteries? I am looking at a brand called Bolt have you heard of them?. How does this battery compare to say a lith or lead acid type. Thanks again I am new to this EV technology but enjoy learning about it as the project i am working on is going to help greatly reduce the polution here in the Philippines.


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## major (Apr 4, 2008)

Ertike said:


> You say you have been playing around with batteries for decades, have you heard anything about this new technology Silicone batteries? I am looking at a brand called Bolt have you heard of them?. How does this battery compare to say a lith or lead acid type. Thanks again I am new to this EV technology but enjoy learning about it as the project i am working on is going to help greatly reduce the polution here in the Philippines.


They don't have a web site up yet. I did find this description "This new battery technology operates by adding a silicate salt electrolyte to a lead
battery, instead of the usual Sulphuric Acid." So I guess it would be just an improved Pb-Acid (or Pb-Salt) battery. Send me some and I'll test them for ya


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## CroDriver (Jan 8, 2009)

major said:


> I just plotted a test.
> 
> 
> 
> ...


If someone wants to make a comparison... Here's some data from our battery tester and a 20S3P LiFePO4 module. 










(Y axis: Volts; X axis: Ah)

The test was performed on a battery-tester which was developed and produced in-house. The voltage reading are directly from the BMS in the module.

We can make a 2C discharge test for direct comparison. 

Here's another example of a 7C test where we where testing the voltage drop on different SOCs - discharge 10%, wait, discharge another 10% etc.


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## major (Apr 4, 2008)

CroDriver said:


> If someone wants to make a comparison... Here's some data from our battery tester and a 20S3P LiFePO4 module.


Hi Cro,

Long time; no see. Thanks for posting. Always good to hear from you. And nice tester----show off 

major


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