Group Buy: Dow Kokam LiPo Cells

[RWP]

Can anyone help with the charger technology for these cells?
Thanks, Roy

[Ypedal]

What i personally want to know, if expected shelf/calendar life.. if kept within spec at all times ( hvc, lvc ) and only used 100 cycles per year, how many years can one expect these cells to last before they give up due to age ?

[neptronix]

Can anyone help with the charger technology for these cells?
Thanks, Roy

Anything that works for 3.6-3.8v nominal charges would be fine. If you run RC Lipo, Konions, etc. ,All your charging equipment will work.

The only special attention that will be required is - what is the max charge voltage on these? If you are using a RC Lipo charger that insists on charging to 4.2v/cell, and these want 4.10v/cell or 4.15v/cell, then that's a problem.

If you have a bulk charger, you will need to adjust the top charge voltage for that reason as well.

Also, what is the C rate for charge? we do not know this - but you will have to account for that is well. Most chemistries can be charged at at least 1C, i'm sure these can be charged at 1C as well, but we need to know for sure.

[Hugues]

...
Also, what is the C rate for charge? we do not know this - but you will have to account for that is well. Most chemistries can be charged at at least 1C, i'm sure these can be charged at 1C as well, but we need to know for sure.

specs for these Kokam cells can be found on this page:
http://mabula.tangram.dnsalias.net/battcomp/cell_info

click on the kokam cell you want, the specs from Kokam will open, for example:
http://kokam.com/product/product_pdf/hi ... _Grade.pdf

max charge amps and voltage are given

[recumpence]

They are 2c or 3c charge capable.

FFR should chime in soon. I can tell you, from my research, these are the best cells on the market for EV use, period. If you go to Metricmind.com and look at his no compromises EV, these are the cells he is using. AFAIK, they are exactly the same voltage as typical Lipo (50.4 volt full charge for 12S). Tom from FFR can confirm this.

Matt

[neptronix]

Got it. Looks like 1 or 2C, depending on the cell.
I think they do not have all the cells listed on the site, but that data is enough.

Discharge rating seems to vary according to Dow Kokam's specs.

Looks like these are 3.7v nominal and go down to 2.7v/cell. The cliff is probably lower for this chemistry and more capacity is located down in the lower voltages.

I'd love to see a discharge graph. We can only make assumptions right now.

http://www.dowkokam.com/tech-cells.htm

"Best-in-class operational life (10+ years)" - ooh, nice

"Made with advanced nickel metal cobalt technology, Dow Kokam battery cells are designed with a patented Z-fold process that ensures precision stacking of the electrodes giving your battery cells lower heat generation and improved lifetime."

There you go, it's NMC.

[Hugues]

They are 2c or 3c charge capable.

...
Matt

not all types, some are rated 1C for charge,
again, see the kokam specs sheet, post above

[neptronix]

I found an interesting Dow Kokam document written by FMA - dated back to the early 2000's. The cells are probably quite different than in 2003-2004, but it's an interesting read.

http://ygdes.com/LiIon/technique/Kokam_LiPo.pdf

It's funny that they mention the 'zone of temptation' on page 44, it's what we call the lipo cliff here on the forums.

When using LiPo packs, we recommend that you:
„ Set the cut-off above 2.5V, or nearer 3V in most situations.
„ Avoid designing your pack so that it has to operate at the maximum allowable discharge
rate.
„ Stay out of the “zone of temptation.”

Hah! FMA wrote the book on lipo management before we even knew what lipo was.

Visit page 38 for a discharge graph of one of their older cells. It has the same cliff and hump near 4-3.9v as turnigy/zippy RC lipo, kinda funny.



^-- 20C 5AH 5S Zippy RC lipo

Big kudos goes to whoever can find a discharge graph of their more recent cells.

[parabellum]

what kind of lipo? lico, limn, other?
edit: thanks david, got it nmc.

[Nuts&Volts]

I believe they are NCM chemistry

[cwah]

I'd like to order but I don't know how to solder these cell together. Is there a tutorial somewhere to learn how to do that? Or would they create the right pack for us? And I suppose a BMS would be required?

ps: I'm interested on the biggest cell with the highest volumetric density (wh/kg)

[neptronix]

Highest whr/kg? try allcell. Only $1700 per kilowatt hour.
Oh, and it's got a lovely 2C maximum discharge rate.

Or RC Lipo.. cheap, but far from perfect and much lower cycle life and not very abuse tolerant.

BTW, i mentioned this in another thread, but here's what happens when a Dow Kokam cell takes an arrow to the knee:

[cwah]

At 1700$/wh it's 70% more expensive than Kokam cells and 3 times more expensive than lipo. At this price I would prefer to stay with lipo
And allcell shelf/calendar life is not proven yet.

[sangesf]

Self deleted

[ohzee]

I'd like to order but I don't know how to solder these cell together. Is there a tutorial somewhere to learn how to do that? Or would they create the right pack for us? And I suppose a BMS would be required?

ps: I'm interested on the biggest cell with the highest volumetric density (wh/kg)

Yea I asked the same question earlier. Seems like bare cells , but I was just hoping.

For pre built packs like this sounds like cell man offers the best product.

[cwah]

I'd like to order but I don't know how to solder these cell together. Is there a tutorial somewhere to learn how to do that? Or would they create the right pack for us? And I suppose a BMS would be required?

ps: I'm interested on the biggest cell with the highest volumetric density (wh/kg)

Yea I asked the same question earlier. Seems like bare cells , but I was just hoping.

For pre built packs like this sounds like cell man offers the best product.

Agree. But A123 cells are still on the heavy side. At 165wh/kg these cells really compete with lipo minus the price.

[mvly]

Wow I just check their 31Ah cells. If I run 14s (51.8V to compare with my nano tech), I get around 21lbs. With wires and all, it should come out to 25lbs. I think my nano-tech with all the wires comes out to be 25lbs, but it is only 22Ah. Looks like these cells are lighter than even the nano-tech Lipo. The nanotechs cost me around 800 bucks with shipping ($700/1KWh). In terms of price, these might be still more expensive than nano tech, but I think it's worth it since we are dealing with stuff from a USA company and much higher cycle life. Wish I have the money for these cells. I guess once my nano-techs dies, I will switch overs. Hopefully they are cheap by then. : )

[neptronix]

Yeah, but your nano tech has a higher nominal voltage, and with total absence of sag at that amp hours, you get even higher watt hours for that reason alone. These will notably sag on a 1C load. Your nanotech will wonder if it's being discharged or not at 1C.

Can't compare amp hours to amp hours here. You have to look at watt-hours. A nanotech is only off by a few percent, really.

[regmeister]

Some spec sheets are online, here:

http://www.edisonpower.co.jp/product/slpb.html

[sangesf]

Self deleted.. I'm done

[cell_man]

The 2C constant energy type cells are 165Whrs/kg according to the specs on the first page. The power cells are 148Whrs/kg according to my calcs, 13% better than A123 20Ah pouch cells. Attached is the data sheet, just to put the info out there so there is no confusion as to how they stack up.

[sangesf]

The 2C constant energy type cells are 165Whrs/kg according to the specs on the first page. The power cells are 148Whrs/kg according to my calcs, 13% better than A123 20Ah pouch cells. Attached is the data sheet, just to put the info out there so there is no confusion as to how they stack up.

(i.e. "my cells" rock.. (e.g. Longer cycle life/higher c-rate capability).. LOL)

[cell_man]

The 2C constant energy type cells are 165Whrs/kg according to the specs on the first page. The power cells are 148Whrs/kg according to my calcs, 13% better than A123 20Ah pouch cells. Attached is the data sheet, just to put the info out there so there is no confusion as to how they stack up.

(i.e. "my cells" rock.. (e.g. Longer cycle life/higher c-rate capability).. LOL)

Well I wouldn't put it quite like that. I just thought it wasn't unreasonable to make some comparisons to what is available. I saw 165WHrs mentioned but some quick calcs on the data in the table in the opening post showed that figure appears to relate to the energy cells, and others seemed to think it applied to the power cells. This isn't a for sale thread, it's in the battery section, hope it doesn't cause anyone offence.

[Ypedal]

Damn.. just noticed.. moving to market !

[o00scorpion00o]

That's about 2kg lighter than the equivalent ping, for an extra 5ah.

Still I'd rather have 2 or 3 times capacity increase over cycle life any day, r.c LiPo for another few years it seems!

I think battery development is soooooo slow, though the Leaf II is supposed to have close to twice the range in 2014, but I bet it will be at least 5 years yet before we will see much of a capacity improvement!

The benefits of greater range far outweigh cycle life, IMO, provided the cost is right.

But funny enough I think the opposite is true for electric cars , which benefit far greater with faster recharges and cycle life!