Fred Marks

Kokam Li Po cell technology across the board has undergone transition to High Specific Energy at high discharge rates over the past year, starting with the incredible KOK 340. The total set of Kokam cells from 145mah to 200 AH is now of a chemistry that permits discharge rates of at least 5C and up to 20C for some cells. These are all listed as cells and in packs at www.fmadirect.com
All Li Po cells have high specific energy at the discharge rates used for rating (0.2C). A cell loses capacity and /or voltage as discharge rate increases and the ultimate specific energy is reduced proportionately. Thus SE stated at low rates that we do not use don’t mean much. Specific energy equals watts delivered over a time period to depletion in watt-hours or watt-minutes divided by the weight of the cell. Don Srull and others have suggested that we should display cell performance in watt-minute terms with weight in grams as we always use to specify weight, so that viewers may make rapid calculation of flight time, etc given that watts demanded for a flight regime and the weight of the cell or pack is known. The attached shows both. These data are preliminary and subject to further review to validate the equations.
Two new Kokam High Specific Energy (HSE) cells are now becoming available to round out the set available for RC. The first is the 2AH HSC 20C discharge capability cell that is scaled up from the incredible KOK 340. Data measured by Don Srull using the type equipment the Navy uses for R&D is attached. Some work remains to be done as soon as the external connect system can be improved. Results will be updated at that time. Because the output tabs are over 0.5 inches wide and heavier, the SE for the 2AH is a bit lower than for the KOK 340, but still far greater than that available from other cells tested the same way and using the same type equipment. At 30 amps, the cell still produces over 90 % capacity. This means that models demanding up to 40 amps can be flown using a single pack (1P) without the need to parallel several packs to permit that discharge rate. Typically, one must parallel, say , four packs of a 2.1AH cell= 8 AH of the older technology Li Po cells that can handle only 4 or 5 C, such as the KOK 2000 standard cell, Thunder Power, et al. This means four times the weight and four times the cost. Lower weight translates to longer flight time for a given pack.

The second cell is also 2AH, but is a new “Slimline� configuration that is a drop-in replacement for Sub C packs. That is, the cell width is equal to the length of a Sub C cell. This cell sustains 15 C. Roland Park of Korea sent a post that shows the discharge performance of a 3S pack. The curves are presented in the second attachment. Roland sent a full report in Word format. However, about half is still in Korean. Mr Hong visited our facility this week and promised to translate the report so that it can be posted.

Greg Covey

Great news, Fred!

I can only imagine what a 3s pack of the new 2AH HSC cells will do to my 100mph Kavan ProJeti after dropping half a pound in weight!

Stop back after the WRAM show and let us know when these cells will become available.

Greg Covey

I touched some of the new cells at the WRAM show in White Plains last weekend. After the nickel tabs are welded on, packs will be made. They should be available very soon.

FMA is adamant about wiring the cells to circuit boards to remove any stress from the cell tabs before making packs.

These new cells are the Big Brother to the Kokam 340mAh SHC cell and will be the next step in revolutionizing larger electric-powered planes.

Peter Khor

My Feedback: (4)

Why the change in the graphing method from "% Nominal Capacity" to SE? The prior method was easier to understand for consumers from an application standpoint.

Greg Covey

Hi Peter,

That's a good question.

From my understanding, it was made for military use to show that the specific energy density charts could hide certain traits about cells. Some cells, although lighter, cannot perform at 15C to 20C like the new Kokam SHC (or HSE now) cells. In other words, the capacity for the weight looked better but only on lower current draw applications. More cells are needed to increase the range of current delivery.

Sprink

Sounds just like the cell we need .

Any idea what the weigth per cell is?

Greg Covey

I believe the 2.1AH cell weighs 68 grams (2.2oz).

There are several other ones that i'll look up too.

Dr Kiwi

Any ideas as to when FMA (and others?) might have these 2100 HSE packs available? Cost?

Cheers, Phil

Fred Marks

We find that the nickel tabs have to be welded to the aluminum. I thought perhaps we could go straight to a copper bus, but weld tips available right now are copper so would stick. Surely would be nice if ceramic could be made to carrry high current. Tomorrow is a promised day by the welder to run the tests we need. If all is well, we will turn him loose to weld packs. We have a few hundred cells in stock for now that will be converted to packs asap. We want as much weld area as possible.

Fred Marks

Experimented with pack welding on Friday and expect to have cells for discharge tests at 40 amps this Monday. Will keep you posted.

patternflyer1

My Feedback: (11)

So lemme ask this. Does that mean that the kokam 340 3 cell will outlast the etec1200 3 cell in flight time? Any idea of the weight on the 340 pack? Thanks, Chris

Greg Covey

Chris,

The Kokam 340 cell has a 340mAh capacity and the E-tec 1200 cell a 1200mAh capacity. The E-tec cell is 3.5 times the duration within rated current delivery.

You can view the weights of the Kokam 340 packs [link=http://www.hobby-lobby.com/kokam.htm]here[/link].

mvigod

Greg,

I've also got a 100mph projeti I'd love to test these things out on. Should be very interesting! Also I converted my Extreme Flight Mini 3D to electric and I'm running a 3S 2P (1500mah, 11.1V) kokam setup. I'm guessing with these I can just go 3S 1P?

Greg Covey

Hi Marc,

Yes, that is what we are hoping for and why this new cell has us so excited. It will revolutionize e-flight setups one more time!

Now, if we could just get Fred to stop hording them...

patternflyer1

My Feedback: (11)

I see. That's exactly what I thought. I had people telling me they would be a better pack than my etecs for my 3dx. Thanks for clearing that up before I bought any!!!!!!! Chris

rmh

I have 340Kokams - 3s/3p setup
Also 1500 Kokams.
On my little thrust stand with the Whattmeter hooked up- the 340's can shove 16 amps into my 5400 Himax and deliver thrust into the 30 oz range (prop sensitive).
The BUT is -- the 3s 1500 Kokam does very well and lasts a lot longer . and in power to weight to duration - seems to be the handiest pack around--for my 11-13 ounce models.
This new stuf sounds veeeery intelesting--
My 340 setup sure puts out -but it is kinda like a 3 oz glass of good beer --

Greg Covey

Basically, the new Kokam cells use the same building technology as the 340SHC cells. There will be a 1200mAh cell and 2000mAh (or 2AH) cell. The advantage here is that you won't need to parallel as many cells to get larger packs so it will be less expensive.

The new 2AH cells will be available soon. Packs are being made now by both FMA Direct (aka Kokam USA) and Kokam in Korea. Bigger 4-cell packs (and possibly 5-cell) are being made in Korea now so they should be available here soon. Several of the 4-cell packs plugged in parallel will power the bigger outrunner motors and very high Kv motors like MaxCim 13D, Aveox, and Hacker series.

tetra

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