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| Kokam 3S 2000mAh Lipo | |||||||||||||||||||||||||||||||||||||||||
| The following is a brief overview of the Kokam 3S 2000mAh 15C pack. My thanks to www.aurorra.co.uk for the supply of this pack for testing. |
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| The pack has the following specifications : Connector : Ultra Deans Size : 80x45x26 (mm) Weight :173g In terms of size the pack fits snugly in the canopy of the T-Rex, the fit is such that the pack doesn't need securing in place as the canopy holds it firmly enough. The weight of the pack is slightly on the heavy side for a 3S pack but nothing to be of major concern. The pack is rated as a 15C continuous current pack, which gives it a max continuous current of 30A. The pack will be labs tested as per usual on T-Rex Tuning but as I had two of these packs I have also been flight testing and generally using this pack as my day to day flight pack. So far I have been VERY impressed with this packs capability. A good example of which was a recent motor test (soon to be published) where the motor maxed at an amp draw of 25.6 amps. Most packs would suffer from thermal problems and voltage drop at this kind of current level. The Kokam came off the test at 40 degrees C (104 degrees Fahrenheit) not only that but during the test it's lowest recorded voltage was 9.8 volts, which is absolutely superb. I followed this test with a carbon blade test which drew 30+ amps and the Kokam even managed to stay cool and hold it's voltage in that test as well. Most impressive. I decided to run the Kokam head to head against my usual Tanic 3S 2220mash pack and the following graphs represent the results. Bear in mind that both these packs are rated to similar maximum current draw. The test was conducted by running the Medusa motor up to full power/full pitch and recording the results. The only factor different in these tests is the lipo, everything else was the same. Also worth noting is that the Tanic pack has had more cycles than the Kokam and is therefore not as 'fresh', however, I went back to early motor tests to look at the figures the Tanic returned and the results were slightly better but not wildly different to results recorded below Key to the graph : Blue : Kokam Green : Tanic |
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| As can be seen the Kokam provided more current, dropped less on voltage and allowed the motor to achieve greater overall power. The recorded max/min values were as follows : | |||||||||||||||||||||||||||||||||||||||||
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| This test gave me a good indication of just how much more capable the Kokam
is over the Tanic. This lab test which is available for download also shows
a similar excellent set of figures. In terms of flight times this is very dependent on the motor and it's average amp draw, given this I will not be giving a flight duration figure but will say that the Kokam does turn a very respectable performance in no small part due to it not over heating and staying very cool throughout the flight. Right now the Kokam is top of my list in terms of recommended packs, it's a new generation cell and will out perform most cells on the market based on the limited testing I have done. Based on the lab test I haven't seen another pack that can even come close to the amp and temperature capabilities of the Kokam. Being lab tested at the same time are the new Thunder Power pro-lites, it will be interesting to see how these two packs compare head to head. I don't have the 3S results but the same cells in the 4S pack did do very well but didn't have the same cool running capabilities of the Kokam at the 20A constant load. The only negative comment I would make is that the Kokam does not have any balancing connectors. Over time the pack 'may' go out of balance and there is no facility to maintain the balance of the individual cells in the pack. Aurrora who provided the pack make a very good case for not needing a pack balance connector. The basis being that providing the following conditions are met the pack will stay in balance. Extensive testing of any Kokam type of cell by FMA has shown that to achieve
over 400 cycle lifetimes the following must occur:
The cells assembled in the packs @ the factory must
track on discharge to better than 2 millivolts.
The packs must strictly never be charged faster
than 1C
The packsmust never be overrun past the continuous
current rating.
Charging at greater than 1C for even a small amount will degrade equalisation
in the pack quickly. Excessive current draw will degrade the cell capacity.
As soon as the cell's capacity is degraded you will ruin equalisation when
it is in an assembled pack on every charge .
Given that the Kokam has performed to specification in all the other tests I have no reason to doubt these figures. My only remaining concern in this area is that in the event that the pack is accidentally overcharged/discharged the user has no opportunity to try to rebalance without the balance connector. However, given the information above this might be pointless anyway. I think I'll leave this one for the individual to decide as to what they prefer. Last of all this pack is slightly heavier than it's direct competitors but this is a premium I would gladly pay for the fact that this pack is going to last longer due to it's great thermal capabilities under heavy loads. The conclusion has to be that this is the best pack in terms of power and thermal capability (by a significant margin) that TRexTuning has tested and will be the benchmark by which all future packs will be judged. If you have the Kokam 3S 2000mAh please rate it below. |
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