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Old Aug 04, 2012, 12:40 PM
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United States, NJ, Roseland
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Lipo health? Is it voltage or capacity remaining?

Hi,
Did a 6 min flight and came down with 3.82 on my 6s 5000 on my trex 550. When I went to put a charge on the pack it only took about 2900 mah. Now that's not down to 20 %. Why is my voltage down but my remaining capacity on the high side? Could I have flown for another min or so? What should I be more mindful of the voltage or capacity?

Thanks
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Old Aug 04, 2012, 01:10 PM
Space Coast USA
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Space Coast
Joined Oct 2000
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It's the voltage that counts if we are talking about damaging the pack. However in your case your numbers agree roughly..

Using my chart, 3.82V is about 46% left or 2300mah.

5000mah -2300mah = 2700mah used and needed to fill it back up. (You said about 2900mah)

So you used 2900mah in 6 min which is 483mah/min. You have 2100mah left but only want to use 80% of the packs capacity which would be 4000mah. Of that 4000mah you have used 2900mah which leaves 1100mah to use yet. Divide that by your use rate (483mah/min) and it says you can fly for another 2.3min.
I'd try flying for another 1 1/2 min and measure again.

Somenody check those calulations
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Last edited by hoppy; Aug 04, 2012 at 01:18 PM.
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Old Aug 04, 2012, 01:40 PM
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United States, NJ, Roseland
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Ok but I thought roughly 3.80 is where you want to stop flying as 3.80 under load is around 3.30v or so..........according to your calcs I can fly for another 2 plus min. Which would be great.
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Old Aug 04, 2012, 01:53 PM
Southern Pride
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Haralson County GA. USA
Joined Oct 2004
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That is why capacity uesd is nore accurate that resting voltage however remember as the LiPoly wears it looses capacity so 80% today and 80% 50 flights later may verwell not be the same.

Your car may have a 16 gallon fuke tank and fuel gage may say 1/2 but that does not really mean it needs 8 gallons to fill it up.

Even chargers that have a very accurate fuel table developed for a certain brand and C rating LiPoly are not allways all that accurate especially during the early stage of a charge..


Charles
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Old Aug 04, 2012, 01:54 PM
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United States, CA, Westminster
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I usually fly till the packs is about 3.70 - 3.75V after I come down.
At 3.82V you will have a lot of capacity left.
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Old Aug 04, 2012, 02:02 PM
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United States, NJ, Roseland
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Ok now let's carry this further.....you never want to go. Below 3.0 volts per cell right? Now is that RESTING voltage or UNDER LOAD voltage? My LVC is set to about 3.1 volts or so and I never get near it,
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Old Aug 04, 2012, 03:25 PM
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Better would be 3.3V/cell under load. 3.1V/cell is frowned on these days.
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Old Aug 04, 2012, 03:50 PM
Southern Pride
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Haralson County GA. USA
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I have numerious discharge graphs posted in the Battery graph vault which clearly show many lipolys produced in recent yeatrs delivering over 90% of their capacity at failrly decent loads down to 3.3 volst per cell.

Some Lipolys should not be discharged below 3.5 volts per cell under what are a typical flight loads for many aircraft in order not to exceed the 80% discharged state.

As I have posted for over 7 years now LVC is a moving target and should only be used as a crutch for those times when you forget to set a timer. Most high C Lipolys will have many cycles reduced from their life if flown to 3.0 to 3.3 per cell especially under a light load.

Here is a graph that is 6-1/2 years old when 15C LiPolys were the hot ticket. Todays 20,40.50 65 C ones deliver a greater percentage of their capacity at higher discharge rates.

http://www.rcgroups.com/forums/showp...68&postcount=1

Charles
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