The Ragone Plot for Currently Available RC Cells

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1. This is the progression by Kokam as Li po cells were introduced to RC. The original KOK 3270 was a 5C cell that is very light and has excellent energy density but that can not handle very much current drain. By paralleling 2P, about 20 amps can be supported. Most competing cells fall in the lower chart.. Few have gotten out of that zone thus far. The KOK 3250/5C , a 1st generation Kokam cell, has excellent specific energy but dies as you demand higher current. Trace on down to the right to the purple dotted line to see a particular cell with almost the same chemistry. The three dotted line cells here below it are typical. Let me say right now that these cells all work OK for low current drain. You reduce current drain by paralleling.
2. KOK produced a 2nd generation family that was good for 6 to 10C. The KOK 350 was the first of the third generation cells that has good specific power at low current drain but holds it flat at high drain up to 6.8 amps. The KOK 350 is one of the most popular cells in use today. The KOK 1500 was a transition cell that has outstanding specifics and carries well out to over 1400 watts/kg. The KOK 1500 is the most popular cell for park flyers. Some suppliers are now promising cells that may fall in the yellow band but only Kokams are in stock.
3.The entire new 4th generation of Kokam cells sweeps up and to the right. Up and to the right is better!
Why is it better? You can fly more airplane with less batteries and less cost, recharge in 20 minutes, and cell balancing permits this to be done. An example next frame will illustrate.
4. Our friend Don Srull speaks of the “ten minute line” and feels that is optimum for the HDR cells. That is, you fly one pack for ten minutes while you charge another, pick up your airplane, check it over, socialize, etc and keep flying all day. The ability to charge in 20 minutes with the SKYVOLT balancing charger and Kokam HDR cells makes this possible. This lets you use the pack as 1P and minimum weight.
5.The GP 3300, that is the very best Ni Mh available today, shown at the bottom is compared as apples to apples by taking the weight of the three cells that it takes to produce the approximate 3.7V that one Li Po does. Now you see the tremendous advantage that Li Po has over Ni MH. Ni Cd is far off the bottom scale since Li Po enjoys the advantage of almost five times the specific energy. The data for the GP 3300 based on zapped cells are taken from measurements by Steve Neu. A 3P pack of Li Pos that equals the weight of the 3S1P 3.3 AH Ni MH can deliver a peak of 192 amps. At an average 3.2V/cell at that drain, the wattage delivered is 3.2X192=576 watts/cell; almost 0.8 horsepower.
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