Kokam 30C T-Rex 450?

[redgiki]

I've been trying to locate a Kokam vendor for the current generation of Kokam batteries since FMA Direct and Kokam ended their relationship a couple of years ago. All I've found is dwindling and discontinued stock at Tower Hobbies and elsewhere, and all of it was Kokam's older stuff -- 20C and lower -- leading me to believe the batteries are already a couple of years old.

Just today, though, I found that Hobby-Lobby is selling new 30C Kokam batteries:
http://www.hobby-lobby.com/kokam.htm

Has anyone given these a try yet in a T-Rex 450 or similar aircraft? Given their reputation and good performance in other applications, I was wanting to give them a try, but I'm not certain I want to be the guinea pig at $90 for the 3S 2100mAh pack. If nobody else has tried it, well, I can save up my allowance for a month and buy one. Still gotta be a whole lot of battery for 3X the price of the cheapies...

Anyway, there's a review here (http://www.elektromodellflug.de/akku-test/kokam-30c.htm). For those who don't read German, basically it says they are 30C constant, 60C burst, and can be charged without affecting lifespan at up to 2C. They are supposed to be more tolerant of physical abuse than most other chemistries, and there's a test on the Kokam site of a nail being driven through the cells with only smoke and no flame, and are apparently guaranteed against flame even if over-charged or crash-damaged. As far as heat and discharge goes, they are apparently rated for up to 20C with nothing but ambient cooling, and 25C-30C with active cooling.

They come in a bit on the porky side for a 3S 2100mAh LiPo:

Kokam 3S 2100mAh 30C: 193g
Zipp 3S 2200mAh 15C: 168g
Thunder Power "Extreme" v2 3S 2200mah 25C: 170g
A123 3S 30C: 210g+
FlightPower Evo 30 3S 2000mAh: 175g

[John Heli]

Here in Germany these packs are flown a lot. What I can say from my experience flying a 4s / 3200mah in a Lepton:

- Great power at the beginning, dropping continuously over flight time
- If you charge at 2C, you don't get the full capacity
- A little higher weight than other manufactures
- Staying cool at 10-15C continuous with higher peaks
- Very low cell drift

Compared to my Saehan pack I would prefere the Saehan. They keep the power over the whole flight time and have similar characteristics including safety. The thing Kokam is famous for is the amount of cycles you can use them. I have heard from far beyond 250 cycles, but I have no experience with this.

Hope I could help.

[RC Accessory]

I use the 30C 4000 Kokams in my Showtime 90 e-conversion. A few things you need to understand. The higher the C rating the heavier and larger the packs will be. Comparing them to a 15C is useless.

The Kokam 30C packs may very well be the best lipo battery available and you pay for that quality. Few people are willing to spend that kind of money for Kokams. My packs come down after an 8 min flight at 115 degress and are always perfectly balanced. I charge them at 8 Amps (2C).

[redgiki]

Cool, thanks for the heads-up on usage. Weight isn't my main concern: cycle life is. At around $100 for the packs that I usually pick up for $30-$40, it would need to last at least 200-250 cycles vs. the 100-150 I usually get out of the cheapies.

Balance is a defining factor in pack quality, for sure. Inevitably, the balancer blinks like mad while charging my lower-quality batteries, but often stays off just about the whole time on certain brands of packs.

I'll have to check out some CBA graphs of the discharge curve. If it's actually a fairly linear drop-off rather than the "shelf" I'm used to, that may be a concern...