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2 Lipos packs similar but what really counts:

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Old 03-13-2011, 07:03 PM
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Electriceddie
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Default 2 Lipos packs similar but what really counts:

Hi All,


of the 2 listed batteries below. All is the same except for the 20C vs. 30C rating. If all is equal except for the 20C and the 30C what does that mean power wise? What exactly does the "C" rating mean here with a difference of "10C"?


a. FlightPower - EONX30 (Lite) LiPo - 3S, 11.1V, 1200mAh, 30C - wt. 4 oz.

b. Great Planes - ElectriFly LiPo - 3S, 11.1V, 1250mAh - 20C - wt. 4 oz.


Thanks

Ed
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Old 03-14-2011, 05:29 AM
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Walt Thyng
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Default RE: 2 Lipos packs similar but what really counts:

"C" is the Capacity of the LiPo in milliamp hours (mah). In your case 1200 & 1250. "C" is used to calculate the charge and discharge rates of the battery. Unfortunately it is necessary to convert milliamps to amps for this purpose. Your packs are 1.2 and 1.25 amps. Charge rates for most batteries are "1C"; i.e. 1.2 & 1.25 amps. A "20C" pack can be discharged at 20 times the capacity; a "30C" pack at 30 times the capacity. So your Flightpower can be discharged at 36 amps continuous and the Electrifly at 25 amps continuous. Most packs can handle a very brief burst discharge at a higher rate.

Now for a reality check. "C" rates are often grossly overstated, so most experienced R/Cers never exceed 80% of the stated values unless they have fairly sophisticated testing equipment. Resistance and the associated heat are the major determining factors. A LiPo should never exceed 140 degrees.

Hope this helps a bit.
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Old 03-14-2011, 08:25 AM
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SteveR3750
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Default RE: 2 Lipos packs similar but what really counts:

Sorry, I am a complete Newbie as well....Am I understanding this correctly by assuming that... the Higher the "C" rating the more power you will get out of your battery, but the faster the discharge rate, and shorter the flight times?

So.. .If I want more power... a 30C or 35C battery would provide more than a 20C battery but at 1250 MAH the 30C would not provide as long of flight time as the 20C would...correct?..

Ugh... Thats a tongue twister...
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Old 03-14-2011, 01:25 PM
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Default RE: 2 Lipos packs similar but what really counts:

In the question of whether or not the "C" RATING matters it depends on how close to that rating you are running. If you happen to be running 4-5C then the difference may not be noticeable in flight. Measureable though as the voltage and potential power would be slightly higher with the higher rated C.

If you happen to be running close to the 20-30C number then the difference is more noticeable and the 30+ C pack may even be a necessity.

For stever3750 the same applies. It depends on how close to the rating you are actually running. As for the runtime question it works like this: If you USE that extra power throughout the run then it is true the pack will discharge quicker and have a shorter flight. If you were to USE identical power by throttling back a touch with the stronger pack then it would actually be a longer flight.

hope this makes some sense.
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Old 03-17-2011, 06:36 AM
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Default RE: 2 Lipos packs similar but what really counts:

ORIGINAL: Electriceddie
If all is equal except for the 20C and the 30C what does that mean power wise? What exactly does the ''C'' rating mean here with a difference of ''10C''?
The difference is the IR=Internal Resistance of the cells. The higher the C rating the less IR so it can be discharged at a higher rate without the cells getting overheated. Thus the thinking also goes that a 2200mAh 45C rated LiPo can be charged at say, 4C(8.8amps), just as safely as a 2200mAh 12C older generation pack at 1C(2.2amps).

The IR of the latest generation 45C LiPo may be as low as 1.3, whereas, the IR of a growing older previous generation pack could be 6.3 or more. If you have an E-flite Cell Checker you can get an idea of the difference in IR from one cell to another. For the sake of an example let's say at a LVC of 9.0v the voltage in each cell of your Electrifly 1250 20C were as follows: 2.65v, 3.23v, 3.12v = 9.00v ... cell1 having less IR is depleted sooner; whereas cell2 has the higher IR. Unfortunately, Cell1 being the better cell from an IR standpoint may also be the cell with a shorter, less lively cycle life if 90%+ of the pack's capacity is always depleted by a pilot that wants to fly as long as possible (until 9.0v LVC).

So, even though you balance charge this Electrifly 1250 20C pack to equal cell voltages of say 4.15v, 4.15v, 4.15v the pack is still not truly balanced because of the IR imbalance difference between cells at the moment of a 9.0v LVC ... Cell1 having the least IR and therefore may actually be closer to a 25C discharge rating; whereas Cell2 may actually be closer to a 15C rating. And Cell3 with a 20C discharge rating ... overall the distributor could rightly label this LiPo pack as having a 20C discharge rating.
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