lipos

[cdkoho]

hi can someone explain what 20c-25cand 30c means on lipos which is better any why.

thanks

[odieser]

I believe the 20c and 25c etc. are the output rating of the battery.
Lets look at it this way
The Mah ( example 2200) is the fuel tank capacity
The Voltage ( example 11.1 V) is the size of the engine
The C ( example 25C ) is the horespower

I hope this helps.
Mark

[michael88997]

a 3 cell 2200 25c can put out more amps constantly than a 3 cell 2200 20c, now a 3300 20c can output more because its a bigger battery

[odieser]

why is that michael explain

[redgiki]

There is no regulation regarding "C"-ratings in the battery industry. It is purely a self-made benchmark. In general, higher C-ratings hold their voltage under load better, and develop less heat at the same load than, lower C-ratings from the same manufacturer. Few accurate C-rating comparisons can be made across manufacturers. For battery longevity, size your power system for a sustained discharge below 10C on most LiPo batteries. This equates to a 6-minute flight, minimum. Few batteries will last more than a few dozen cycles with full-discharge times less than 5 minutes.

There are some few exceptions to these rules. A123 batteries, for instance, can still last a thousand cycles or more with 3-minute discharge and 8-minute charge times. Although LiPos have had some considerable advances in the last two years, the longest life-cycle testing I've seen in controlled circumstances was 452 cycles on a Kokam KOK2000 in 2005 (http://www.rcuniverse.com/forum/m_3559995/tm.htm) when discharged @ 10C and charged at 3C. In identical testing circumstances @10C/3C, Thunder Power cells fell over in less than 100 cycles (around 30 cycles with 3C charges, around 80 cycles with 1C charges).

So to sum up: size your power system for a minimum of 6-minute flights (preferably longer). Don't discharge below 20% capacity doing so. Treat the C-rating as how well it maintains voltage under load, and how cool the cell remains under such voltage.

And, in general, "extreme" discharge LiPos -- "25C" or above -- last much less than 100 cycles before losing their strong discharge. I normally size my power systems in my helis with a plan to retire the batteries to my lower-discharge planks after 100 cycles.

[Migs]

Here is a good explanation of the C rating:

http://www.rcgroups.com/forums/showthread.php?t=209187

Migs