# High Power KOKAM batteries: Peak Current works?



## gonuc2 (Aug 27, 2010)

Hi all,

In my future application, I will use High Power Kokam 100Ah batteries:

-	Nominal=100A.h
-	Continous Current = 500 A
-	Peak Current = 800 A (10 seconds)
-	Charging Continous Current = 300 A

Have any of you used High Power Kokam batteries and/or can confirm if it is possible to reach these current values as they say? My project depends on this peak and continous current data and I don’t want to waste my money as they are really expensive!!

Thank you for your help.


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## rillip3 (Jun 19, 2009)

gonuc2 said:


> Hi all,
> 
> In my future application, I will use High Power Kokam 100Ah batteries:
> 
> ...


These are lithium polymer batteries - pretty high end stuff. I have not seen anyone mention using these before on the forum and doubt they would have been used, as they're pretty new (read: expensive).


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## major (Apr 4, 2008)

gonuc2 said:


> Hi all,
> 
> In my future application, I will use High Power Kokam 100Ah batteries:
> 
> ...


Hi gonuc,

I have used the 40Ah cells. And tested them. See http://www.diyelectriccar.com/forums/showthread.php/lithium-battery-monitor-39708p4.html post #35. I have gone up to 8C and discharged them continuously at that rate to about 30% SOC. A lot longer than the 10 second spec. They got hot, but didn't fall on their face or anything. 

Like you say, they are expensive. And you must package them correctly. But they look like a very good cell for power, and energy.

Regards,

major


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## major (Apr 4, 2008)

rillip3 said:


> These are lithium polymer batteries - pretty high end stuff. I have not seen anyone mention using these before on the forum and doubt they would have been used,


Hi rillip,

Do a search for Kokam on this forum and you get a bunch of threads. Here are a couple: 

http://www.diyelectriccar.com/forums/showthread.php?t=44430&highlight=kokam 

http://www.diyelectriccar.com/forums/showthread.php?t=37818&highlight=kokam 

http://www.diyelectriccar.com/forums/showthread.php/lithium-battery-monitor-39708p2.html

Regards,

major


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## gonuc2 (Aug 27, 2010)

major said:


> Hi gonuc,
> 
> I have used the 40Ah cells. And tested them. See http://www.diyelectriccar.com/forums/showthread.php/lithium-battery-monitor-39708p4.html post #35. I have gone up to 8C and discharged them continuously at that rate to about 30% SOC. A lot longer than the 10 second spec. They got hot, but didn't fall on their face or anything.
> 
> ...


Thank you major, your positive test will help me to decide. What I need now is the money 

In the next months, I promise to inform in this forum about my experience with them.

Regards,
Gonuc


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## frodus (Apr 12, 2008)

as with all batteries, don't expect to get the same energy (Watt-hours) at 500A as you would at 100A. If you need power, design around power. If you need energy, try to keep the discharge as close to (or below) 1C as possible, to get the max energy from the pack.


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## gonuc2 (Aug 27, 2010)

Frodus:
Thank you for your advise. My project is oriented on high power, I know I won't have so much energy until some kind of super batteries will be launched.

All: 
Another question regarding this post is about regenerative brake: as the charging current is 300 Amps, I think the regenerative brake will be limited for that. Of course I have friction brake, but I am afraid I won't be able to motor-decelerate as much as I accelerate, unless this charging current could be higher for short periods of time.


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## rillip3 (Jun 19, 2009)

gonuc2 said:


> Frodus:
> Thank you for your advise. My project is oriented on high power, I know I won't have so much energy until some kind of super batteries will be launched.
> 
> All:
> Another question regarding this post is about regenerative brake: as the charging current is 300 Amps, I think the regenerative brake will be limited for that. Of course I have friction brake, but I am afraid I won't be able to motor-decelerate as much as I accelerate, unless this charging current could be higher for short periods of time.


In previous discussions about a racecar using regen, the proposed solution was to dump excess energy to a heat-dissipating resistor when the batteries could not handle it. Might want to check this thread: 

http://www.diyelectriccar.com/forums/showthread.php?t=47459&highlight=regen%2C+braking%2C+race


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## RoughRider (Aug 14, 2008)

do you get them directly from Kokam?

or where do you get the cells from?


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## gonuc2 (Aug 27, 2010)

RoughRider said:


> do you get them directly from Kokam?
> 
> or where do you get the cells from?


I have had an offer directly from them. They send me the cells directly in Spain, where I am. Sincerelly I don't know if they have a reseller here in Europe, nor US.. Major can confirm.


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## DavidDymaxion (Dec 1, 2008)

The ProEV guys used Kokams:
http://www.ProEV.com


White Zombie http://www.plasmaboyracing.com is now using Kokams and just set a 10.4 s 1/4 record! This is faster than a stock Corvette or Ferrari, and he did it in a street legal car!


gonuc2 said:


> Hi all,
> 
> In my future application, I will use High Power Kokam 100Ah batteries:
> 
> ...


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## Crash (Oct 20, 2009)

I've been looking at Kokam batteries for a while. But I've been looking at the large capacity 40 and 70 AH batteries. (Middle column on their web site)

Lately, I've been looking at the A123 26650 cells, and for what I'd want in a car (assuming money was no object) they'd pretty much be perfect due to their weight and durability in large parallel packs. Of course, the biggest issue with those is a workable BMS. 

The specs for my project would be at least 90AH @ 400-420V and a max current of 600A. To achieve that, I'd need 5000 A123 26650 cells (125s40p). That's just mind boggling though. So I started thinking about the high power smaller AH Kokam batteries like the 70205130P which has the following specs:

12AH
Max Charge: 36A
Nom V: 3.7
Cont Discharge: 60A
Max Discharge: 240A
Weight: 354g

This sounds pretty good when you think about weight and less cells to achieve my goals.

It would come out to 960 cells (instead of 5000) in a 120s8p configuration. It would meet my continuous and max current goals by a long shot, and would yield 96AH (correct?). 

If I'm correct, the currents would be:
Cont Discharge: 480A
Max Discharge: 1920A
Max Charge: 288A

That would be great for regen braking as well. Although, the current certainly isn't as forgiving as the A123 cells, it is certainly more than my project would need.

But the best part is that it would be easier to balance (and would require less BMS equipment) and even weighs in around 340Kg which is 10Kg lighter than a 5000 cell A123 pack.

The WH/Kg for the Kokam pack would be 125wh/Kg and the A123 pack is 108wh/Kg.

Basically, there'd be no reason to go to the A123 cells (especially since they're impossible to find) as long as the Kokam price is about on par.

So, I guess what I'm looking for is if someone has pricing on the Kokam 70205130P cells.


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## major (Apr 4, 2008)

Crash said:


> But the best part is that it would be easier to balance (and would require less BMS equipment).


Hi Crash,

From what I have seen, the parallel cells groups are assembled first and have a single BMS device attached. Then the groups of parallel cells are connected into the series arrangement. So, either way (Kokam or A123), you have about the same BMS complexity.



> The specs for my project would be at least 90AH @ 400-420V and a max current of 600A.


In which case, why not use 110 of the 100 Ah cells, 80460330H?

And as for the complexity of a battery assembly consisting of 5000 A123 cells vs 960 of the pouch cells, look at the design and process used. The spot welder and copper foil interconnects may in fact make the small cylinder cells easier. Also, energy density figures for pouch cells can be deceiving because they require special packaging to maintain side pressure.

Overall, I like the larger format Kokam cells. But I really have limited experience outside the lab. Just a few months in my yard tractor and only about 4 cycles. And pretty wimpy duty, about 0.7C discharge  Although I do think several of the bikes in the TTXGP ran the Kokams and they held up very well. I'm not sure of what size or discharge, but likely around 4C from the length of our races.

Regards,

major


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## Crash (Oct 20, 2009)

major said:


> Hi Crash,
> 
> From what I have seen, the parallel cells groups are assembled first and have a single BMS device attached. Then the groups of parallel cells are connected into the series arrangement. So, either way (Kokam or A123), you have about the same BMS complexity.


The reason for that is because I don't really like the idea of one BMS board for 40 batteries in parallel. Unless my understanding on how they work in parallel is off. Do they balance each other naturally? The way I see it, unless they naturally balance out while in parallel, you still run into the issue of a single cell within the parallel group being under or over charged. Or can this not happen?

The other reason is because the Kokam cell pack would require less strings in series. The Kokam cells' nominal charge voltage is 3.7 vs. the A123 cells which are nominal at 3.3V. The difference is 5-10 strings in series. (115-120 packs vs 125)

But my understand of how parallel packs work may be completely off as this is the first time I've researched this at all. Up until seeing the A123 cells, I'd never seen a reason to use parallel packs.



major said:


> In which case, why not use 110 of the 100 Ah cells, 80460330H?
> 
> And as for the complexity of a battery assembly consisting of 5000 A123 cells vs 960 of the pouch cells, look at the design and process used. The spot welder and copper foil interconnects may in fact make the small cylinder cells easier. Also, energy density figures for pouch cells can be deceiving because they require special packaging to maintain side pressure.


I'd completely forgot about those cells. I thought about them long ago, but hadn't looked at their specs in a while and forgot that you can sustain 500A with them. I know that ProEV team was using them in their race car pulling 600A constant with those batteries and having no issues with them. I did the math and the weight would be about 310Kg for all the batteries. Then you have to figure out cooling and a way to keep them together really tight. 

Not a bad idea, again, if the cost is lower than the A123 cells.










The ProEV team used "Coroplast" to keep the cells cool. I think that would work very well. I did, however, think about building an aluminum version of the Coroplast which would transfer heat better, but it would weigh a hell of a lot more. Keeping weight down is key.


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## major (Apr 4, 2008)

Crash said:


> The reason for that is because I don't really like the idea of one BMS board for 40 batteries in parallel. Unless my understanding on how they work in parallel is off. Do they balance each other naturally? The way I see it, unless they naturally balance out while in parallel, you still run into the issue of a single cell within the parallel group being under or over charged. Or can this not happen?


Elements connected in parallel have the same voltage across them. This is true whether the elements are resistors or cells.

To finish the lesson, elements in series have the same current through them.

Regards,

major


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## Crash (Oct 20, 2009)

major said:


> Elements connected in parallel have the same voltage across them. This is true whether the elements are resistors or cells.
> 
> To finish the lesson, elements in series have the same current through them.
> 
> ...


OH! OK! That makes more sense then! Thank you. That puts my mind at ease then... This whole time I've been wondering how people are balancing the cells in parallel.

(Door open)

OK, so then, given that the prices were equal, the A123 packs would be better in this case.


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## gonuc2 (Aug 27, 2010)

Crash said:


> So, I guess what I'm looking for is if someone has pricing on the Kokam 70205130P cells.


KOKAM pricing is about Euro0.6/wh (Ex-Works Kokam). I had this pricing on May 2010, and this is for all the High Power and Large Capacity cells.

You have to add the delivery cost from Korea and the dangerous goods packaging.

Regards,
Gonuc


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## Crash (Oct 20, 2009)

That would put a 115 cell pack of 100AH batteries at about $33.3K + shipping... That's almost right on part with the A123s. A little more expensive, actually. I guess that would make the decision a hard one. I think I'd buy the A123's over the Kokam's at that point.


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