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To what extent can i discharge battery and use it again without charging?

Discussion in 'Pro/Adv Discussion' started by skysense, Mar 28, 2016.

  1. skysense

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    This is a big question because dealer who sold me the Phantom told me to always discharge battery fully and replace with a full one before every flight. And if i don't want to do it is better not to turn off the quad/battery.

    Now in my work i often come to situations where i need to take off, make video/take photos (use 20% of the battery), land and move to different locations without of possibility to charge batteries in between flights.

    So, can i for example discharge one battery up to 40%, turn quad off and use the same battery again for next flight?

    I am not concerned for the battery itself as for the thing he told me that there is some kind of bug and if i turn on battery that is for example at 40% there is a possibility that it will shut off and the Phantom will go down.

    Anybody doing this or have some experiences?
     
  2. Erroll

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    I do that all the time, although many will advise you not to.
    Whenever you launch with a battery which is not fully charged, take care to fly gently; simply do not apply full throttle up & out, and keep an eye on the voltage indicator, and you will be fine. Be extra careful in cold temperatures.
     
  3. alokbhargava

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    Your dealer is correct to some extent. Let me explain below.

    Each battery has a predefined discharging characteristics and these are well programmed in P3 FW and are used to predict remaining charge and generate alerts. It's get difficult to predict the discharge levels if you you start for example with 50% charge on the battery and P3 FW interprets it wrongly. There have been several cases where P3 has suddenly dropped assuming battery levels have gone down below the critical levels.

    To take care of such situation, I had long back proposed that one always starts with fully charged battery so that P3 understands discharges well. This method has been very successful and has become a practice now. DJI and the battery manufacturer have to do research to generate reliable characteristics for partially discharged batteries.

    In your case it would be better for you not to turn off battery but you can turn off props during interruptions. This way P3 will continue to follow the last discharge levels. This is more reliable than totally switching off battery. Even then I will suggest don't go below 20-25% charge levels during flights.
     
  4. rockydog

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    You should never fully discharge your battery. Your dealer has given you bad information. You ought to be getting a low battery warning at 30% and landing soon after - maybe around 20%. The only time you should run your battery low is if you a doing a deep discharge cycle, which DJI recommend after every 20 charging cycles - even then, they only recommend going down to 8%.

    @Erroll has given you good advice for using a part charged battery.
     
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  5. tcope

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    I'd say you should be okay. The bigger problem is letting the battery sit in a discharged state for a day or so and rh n using it. The software guesses at the percentage of battery left based on voltage and current drain. So an idle battery might show 40 percent but bases on actual voltage, have a lot less, especially under load. It's going to more accurate when having just been used though.

    In cold weather this becomes much more of an issue.

    Again, you should be okay but it's not recommended.

    That is one smart dealer. He appears to be very informed!

    If batteries are not an issue why not buy 4 or 5 and use a charged up battery each time?
     
  6. PrecisionAeroworks

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    There is no need to "fully discharge" the battery before recharging. That is a hangover from older battery tech. The DJI lipo batteries (like the lipo battery in your cell phone) do not mind being topped off. Indeed, a shallow cycle and recharge contributes less "damage" to the ultimate lifetime of the battery than a deep cycle. The only reason to deep discharge (down to 8% every 20 flights or so) is to let the smart battery software re-calibrate the battery % indicator to reflect the actual capacity of the battery as it ages.

    There have been some issues in the past (particularly FW 1.05) where the aircraft FW was not interpreting the what the battery was reporting correctly.

    There have also been issues, where upon a 2nd (or 3rd) flight on a single battery charge, that the battery percentage indicator was either incorrect, or "stuck". This led to unexpected RTH or autoland behavior for some.

    The first issue (the FW misinterpreting the battery status) has been fixed.
    The second issue, hard to say. However, if you monitor the lowest cell voltage instead of completely relying on the % gauge, you will be fine.
     
  7. tcope

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    Sorry, one more think. I'd highly recommend that you turn on the voltage display and watch the voltage more closely than the percentage. I don't remember the minimum off hand that you want to land at so I won't guess. Someone should have that information.
     
  8. PrecisionAeroworks

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    Absolutely everyone should do this. This option displays the voltage of the lowest cell right below the battery percentage.

    Have the aircraft on the ground BEFORE the lowest cell reaches 3.3V. (Or the aircraft will land itself.)
     
  9. Erroll

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    I agreed completely. Monitoring the voltage will also show how the colour changes depending on the remaining voltage and your flying style. If you are at say 40% it will be yellow, but if you give full throttle you will see it change to red. If you let off immediately to a hover you will see it return back to yellow. ( It is probably safer to experiment at 60% and watch it change from green to yellow and back).
    My point is that it is there for a purpose and practice using it and learning what it tells you.

    Another important point is to set C1 or C2 to show battery status and monitor it regularly.
     
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  10. skysense

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    First thing i did when i got my P3P few weeks ago was that i set my C2 button to show me battery screen, so i can monitor the power source.

    Before Phantom i was using and still am TBS Discovery Pro which doesn't have smart batteries, so i am very well informed about how LiPo batteries work, and there is no sound alert or anything, only what you monitor. Trust me, i know how fast LiPo drains even in descend when you hit around 2.9 per cell :)

    I am not concerned about topping off batteries, and recharging them from 80-90% to 100%. I am worried about this 30-40% power off and on again and fly business. And not leaving them for a few days and then fly again, if i have need to use them at those percentages i will do it on the same day within max few hours.
     
  11. Erroll

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    Well, I can only reiterate my earlier post - flying gently, with no sudden bursts of throttle is key.

    I flew four batteries today. I gave all my apps a workout and landed several times, shut down, changed apps and took off again. Just be sensible!
     
    #11 Erroll, Mar 28, 2016
    Last edited: Mar 28, 2016
  12. PrecisionAeroworks

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    ^^Which is the reason to monitor voltages (which as you say, was the only "gas gauge" we had before smart batteries). It is the calculated % readout that can get jacked up when you restart the aircraft with a partially charged battery. The voltage display is just the raw value coming back over the telemetry and not effected by a restart.
     
  13. skysense

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    Nice to know that, i was worried that there might be some FW problem like Phantom reading voltage wrong generally and thus put the quad down. But if it is as you say raw telemetry, there should be no problem if one monitors voltage all the time and keep % as secondary information input.
     
  14. PrecisionAeroworks

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    This is exactly what was happening with FW 1.05 and fixed in FW 1.06 (or at least this is the story). The aircraft FW interpreted a lower value for voltage than the battery FW was reporting.

    This, coupled with winter in the northern hemisphere, and the voltage sag that happens with aggressive flying in cold weather, led to some P3's falling out of the sky. (i.e the battery voltage would briefly sag to 3.3V on an aggressive move, the FW would erroneously interpret that as 3.0V instead, and shut the motors down.)

    The % value on restart with a partially charged battery is, as discussed, a more subtle issue. But monitoring the actual cell voltages is, in this case, an effective workaround.
     
  15. Reed L

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    It was 1.05.001 update when it was noticed but it may have been the 1.04, either way I agree with what PrecisionAeroworks is saying, so make sure that you aren't running a fw of 1.04 to 1.06.003. Depending on how long it is between flights, I run an inverter in my car and with the 3 battery charger, I can always start out at 100%. I would just pull the battery and put it on the charger between shoots and have no worries at all.
     
  16. skysense

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    I have 1.5.70 on the RC and 1.6.40 on the Phantom. i also have inverter in the back of my car, and extra 74Ah car battery thats only purpose is to charge my quads batteries.
    Problem rises when shooting locations are inaccessible by car and it is not very pleasant carrying 18kg car battery around :)
     
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  17. shockwave199

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    Would a voltage reading of 3.5 occur generally around the 20% mark? If you are flying an easy going flight within around 1,600' or less, perhaps even a slow poi orbit, at what voltage do you tend to call it quits and head back in?