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P3P auto-landed 30 seconds after take off at 42% battery.

Discussion in 'Pro/Adv Discussion' started by SuperRC, Jun 9, 2016.

  1. SuperRC

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    I recently attempted to make a short test flight with my P3P. I didn't intend to stray out of the backyard. I took off at 42% battery, about 30 seconds after take off the P3P went into critical low battery voltage and landed. The battery indicator was showing 2 solid green lights I recall, and the DJI Go app battery was showing 42%. It's did this twice. I was using older firmware. I changed batteries and everything was fine.
    I have since updated to the latest firmware and recharged the same battery with no issue after a test flight. However, I am curious to know why the Phantom did this, and if anyone else has experienced this? This issue is concerning, particularly if someone is quite a distance away.

    I'll try and attach the flight log file.
     
  2. Mimoid

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    The battery percentage indicator is not reliable below 60% and gets successively more and more unpredictable below that point. This is not only valid for the Phantom, but is just the way all "smart" batteries work.

    If you start a new flight with a partially charged battery (like 42%), the charge may drop in less than a minute down to 10%, initiating an auto-land sequence.

    That is why DJI clearly states in the manual that you should always start every new flight with a fully charged battery.

    I would also recommend that you display the actual voltage in the app, not just the percentage. That way you have a better indication of the remaining expected flight time.

    // Tom
     
    #2 Mimoid, Jun 9, 2016
    Last edited: Jun 9, 2016
  3. bLaStErAiD

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    The simple easy and to the point answer, always charge your battery or batteries before you fly if possible, and never fly with a partially charged battery specially if it's been sitting for over a day. In a recent thread me and others discussed this very issue, I suggest you should read the whole thread and at the end posts 175 and 176
    Just lost pro 3 in the ocean.
     
  4. Mark The Droner

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    Yep

    This is a fatal error and a n00B mistake.
     
  5. SuperRC

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    Lol. Thanks for your replies guys. I really do understand that I must always take off with full battery, hence I stated it was literally only taking off in the back yard...just an auto takeoff within 4 square meters, no manoeuvring. I'm more after why this would happen?
    Needless to say, it is a lesson learnt - Always take-off with a full battery :)
     
  6. Mimoid

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    Yes, I pretty much consider a battery charge below 40% as "zero". It gives me some safety margin for the unexpected, like homeward headwind and stuff.

    //Tom
     
  7. SuperRC

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    Good tip. Always take-off at 100% and RTH at 40%. Definitely a good safety margin.
     
  8. Mark The Droner

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    I hate to beat a dead horse, but I'm afraid you may be missing the point.

    There is nothing wrong with flying at 40% or 30% or even 20%. The problem is when you launch with something other than a fully charged battery.

    If you launch with a battery such as the one shown in your video, you are risking a hard landing or worse. It doesn't matter if you plan to fly for five minutes of five seconds.

    Hope this helps.
     
    captainmilehigh likes this.
  9. SuperRC

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    Thanks for the input. I do understand the point, however I was more after why there was a discrepancy between my indicted battery levels and the critical low voltage warning.

    I understand I should always launch with a full battery and I always do. However on this flight it was just a test flight and only planned to hover. Just curious to know why the discrepancy...
     
  10. Mark The Droner

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    That's a good question and if you read through the thread linked in post #3, you'll learn more. To summarize, the battery behaves badly when launched on something other than a full charge. The charge indicated is not to be believed. As suggested by Mimoid above, if your battery is not full charged, pretend your battery has a zero charge and charge it fully. Hope this helps.
     
  11. tcope

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    The short answer is that you probably were not at "40%". If you looked at the actual voltage in the lowest cell it was probably at a the app's critical level. When a battery is sitting idle it will report a high charge. When you start drawing current through it, that charge becomes more accurate. Hence, prior to your take off it looked fine but once you took off and started to raw a good amount of current the battery showed it's true reading. Because of prior issues, DJI has put in place a _ton_ of battery warnings.
     
  12. rene van der meer

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    SuperRC you are very lucky that it safely landed.
    Please use a better title than just "question". Maybe "forced landing after take off with 42% battery"?
     
  13. kenjancef

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    So as a new P3P owner, sometimes it will sit for a week without flying, and I have the discharge set at 10 days. So the safe percentage is above 60% to fly? I usually do short flights as well, and typically my battery reads in the upper 80's to low 90% range. I assume that's safe? If my battery has 2 green bars or less I throw it on the charger.
     
  14. rene van der meer

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    Taking off with a not fully charged battery is asking for trouble.
    I have the discharge set at two days.
    I always charge to 100% before I plan to take off. If I am not able to fly, I know that the battery will not be stored for long at 100%.
     
  15. kenjancef

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    That makes sense... think I'll change to that... because I don't always fly every day (even though I wish I could!!)
     
  16. SuperRC

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    Thanks again. I went and read through the other thread that was mentioned. The point is very clear. Seems like it's not an uncommon issue.
    I'll definitely be monitoring battery voltage closely on every flight. Thanks again for your input.
    Always take-off fully chargered!!! :)
     
    #16 SuperRC, Jun 9, 2016
    Last edited: Jun 9, 2016
  17. SuperRC

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    How can I change the title?
     
  18. SuperRC

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    Done.
     
  19. flyNfrank

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    Ok so here is what happened..... The firmware is now configured so that when the battery volts reach a set point it will force the A/C to land. You likely have a battery with at least a somewhat weak or weaker cell, and that along with the amount of volts drawn at the time of launching upward (extra resources being used) plus the combo of the battery being low to start with....all allowed your setup to reach that set point I just mentioned. Never launch at anytime with less then a fully charged battery. These type of things use to never happen until dji started implementing the smart battery to function the way they had intended for them to function. It has been a rough road getting to where things are now with the smart battery. Many trashed out P3's.

    Btw, if you haven't yet already, you really should read the manual as it will help save you some grief at some point. Just know ahead of time that there is still a great deal of need to know info not in the current manual.
     
    #19 flyNfrank, Jun 9, 2016
    Last edited: Jun 9, 2016
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  20. N017RW

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    Yea,

    The P2's have a 'hidden' 3rd LBC at 10.65 volts for the 2P3S packs they use.

    I tested this with several flights using my Futaba T10J telemetry.