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30C Batteries for F3A

Old 01-06-2010, 09:49 AM
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J-P
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Default 30C Batteries for F3A

Does anybody already gave it a try or know if there is any advantage ( less consumption, identical power until the end of the flight, ....) using TP 30 C instead of TP Prolite V2 20 C for example ?

Happy New Year ......
Old 01-06-2010, 03:59 PM
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Jason Arnold
 
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Default RE: 30C Batteries for F3A

G'day J-P,

Personally I have not used the 30C packs but do use the 20C F3A TP packs. Logic says that if the 30C pack can supply more current then it's internal resistance must be quite a bit lower which would give more punch(current delivery). Not a great advantage for F3A as we're trying to be smooth with our throttle.

My 20C packs can supply 106A continuous and 212A in burst. In F3A we don't get anywhere near these currents. The highest I've seen so far on my AXI is 65A peak on the Jeti box.

One could also assume that if the pack has a lower internal resistance then the cells would run cooler for the same load. The pack voltage could also be slightly lower.. This is where ohms law comes into play... In the old days of NICAD batteries, the low IR cells(SCR) delivered a slightly lower voltage but the extra punch the cells provided offset this compromise to a large extent. I used to race RC cars and that is where you really see the differences in packs.. I think this is the area pushing the C rating development on LiPo batteries..

In my opinion, 30C packs are an overkill for F3A at this point in time. Having said that, future development of motors(bigger) and airframes(more drag) could result in 30C packs being required. Time will tell I suppose.

Cheers
Jason.
Old 01-06-2010, 11:27 PM
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can773
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Default RE: 30C Batteries for F3A

Hi Jean-Paul,

In F3A one of the more important aspects of a battery is the energy density (Wh/kg), we need lightweight, sufficient flight time, total power is not the most important things. C rating does not affect this parameter directly, however higher C batteries are in general heavier which lowers their energy density.

The original Prolite batteries from TP were some of the highest energy density packs produced (the 2000 mAh cell was very high for a lipo), and is the main reason why they worked so well for pattern.

A side benefit of lower C packs is they act as a governor of sorts. In order to get 9 minute flights you have roughly a 7C average discharge rate, with maybe double that as a peak burst on uplines. A 20C rated pack discharging at 7C average cannot burst as high as a 30 or 40C rated pack can. In a lipo the closer you operate to the rated discharge capacity, the less burst capability you have. This is why a lower C pack feels much more consistent in flight. Again this is why the original Prolites which were 13-15C packs felt so consistent because while operating at 7C average they could not produce a large burst of power like some of the modern packs can.

High C packs are good for guys who want to fly for two-three minutes

Hope that helps
Old 01-07-2010, 12:00 AM
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Silent-AV8R
 
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Default RE: 30C Batteries for F3A

High C packs are good for guys who want to fly for two-three minutes
This really confused me early on too. I run large fast electric boats that can pull 200 amps easily. High C packs are a requirement and I can dump a 12,000 mAh (10S2P) set up in 2 minutes or less. Same with my electric glider. 3.2 meter plane, 84 ounces all up with a Hacker B40 FAI motor. 30 C 3S 5,000 pack gives me maybe 2 minutes total run time, which I do no more than 15 seconds at a time.

My 2 meter pattern plane however does fine on 18C to 25C packs giving me 7 to 8 minutes and never really stressing them much. 25 amps or so average load.

High C packs are larger, heavier, and cost a whole bunch more, so I am happy my pattern planes is happy with lower C packs.

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