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LiIon, LiPo, NiCd & NiMh General General Battery Support


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Old 08-04-2012, 12:38 PM   #1
hidaven
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Default Is my lipo ok? Voltage vs mah left?

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?

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Old 08-04-2012, 12:55 PM   #2
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sounds about right try 3.75V and see how much you put back, say another 30 seconds for first try
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Old 08-04-2012, 12:56 PM   #3
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That sounds dead on. You're good.
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Old 08-04-2012, 01:53 PM   #4
hidaven
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Ok but if I'm not near putting back 4000mah which would be then 20% remaining, I shoud get another min. To 90 seconds. Also if I run the pack down to 20 % remaining isn't my pack I voltage going to be lower?

I always thought everyone stopped flying at 3.75 to 3.80 because under load those numbers would be near 3.80. But if I run down to the 20 to 25% level where would my pack voltage be......at any rate what's my biggest concern, mah remaining of not getting near the 3.2 volts under load?
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Old 08-04-2012, 03:52 PM   #5
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There two big concerns. The first is depleting your pack beyond 80%. You aren't close to that. The second is cell voltage under load. If the pack voltage under load drops into the low 3s (I have seen 3.3v average), then either the pack is getting tired, or the C rating for the pack is too low for the application. Resting voltage is no indication of loaded voltage. You need on-board logging to see that. Resting voltage is only a rough indication of the state of charge.3.8v per cell resting voltage is is about 40% remaining.

At your current rate you are burring 483 mah per minute. Divide that by 4000 (80%) and you get a projected flight time of approximately 8 minutes 15 seconds. Just remember that your burn rate is relative to your flying style and headspeed. Start doing a lot of heavily loaded maneuvers and that 8 minutes can shrink it four minutes. Continue to monitor your pack consumption as your skills progress and adjust your flight times accordingly.
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Old 08-05-2012, 09:05 PM   #6
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Quote:
Originally Posted by hidaven View Post
I always thought everyone stopped flying at 3.75 to 3.80 because under load those numbers would be near 3.80. But if I run down to the 20 to 25% level where would my pack voltage be......at any rate what's my biggest concern, mah remaining of not getting near the 3.2 volts under load?
The pack spends a fair amount of time at ~3.8V (about 1/3rd IIRC) I have noticed my packs are close to 80% when they are at ~3.75V. The capacity is the main thing really, your voltages make sense, fly for another 30s and check voltage, ill wager its still ~3.8V.
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