Welcome to InspirePilots.com

Join the leading DJI Inspire community for free!

Battery calibration and cell voltages

Discussion in 'Inspire 1 Help' started by Mr Phantom, Aug 30, 2015.

  1. Mr Phantom

    Joined:
    Jun 19, 2015
    Messages:
    294
    Likes Received:
    25
    I have just finished what i thought was a calibration of the battery, but i just read that it needs to be a continuos discharge?
    I powered off the aircraft two times during the 4-5 hours it took to discharge the battery in the drone by keeping the drone powered on but the motors shut off.
    So have i not done a calibration, do i need to do it again?

    My second question is about the battery cell voltages, I also saw somebody had written that the cells on the Inspire 1 battery is charged up to 4,4 V? I´m pretty sure that my highest cell voltage was 4,31 when it had discharged the battery and then charged up to 100 percent, and my battery is brand new it has only 1 charge cycle.
    Right now the DJI GO app is showing 94 percent battery left and the cell voltages is between 4,24 and 4,27, does this sound normal?
    And what is the accepted difference between individual cells?

    I would really appreciate some input, thanks in advance.
     
  2. John Alan

    Joined:
    Apr 10, 2015
    Messages:
    225
    Likes Received:
    62
    Location:
    Central IL - USA
    What I stated in the other thread (will relink here for future reference of others) is my opinion...
    Mod values, IMU, etc.
    Suggest others read there... then come back HERE to comment on it if they want...

    As to acceptable differences... not sure...
    My gut reaction is your battery needs some exercise under load and then later a ~3.4v discharge (in hover) and full recharge (as discussed) before drawing any conclusions...

    All batteries (I currently have 6 active... 2 47's and 4 48's) act slightly different...
    They all have "personality and character" as I say...
    One of my 48's will draw cell 3 down a bit more then the rest... but not by much...
    Am i worried... no, it still works to my expectations... 15+ mins flight time to 25%... good enough... ;)
    It still flew just under 20 mins during it's last discharge flight... So I'm fine with it...

    My opinion why DJI mandated the immediate discharge/recharge was all the batteries in use that the numbers were out of wack on after several cycles...
    One of mine showed -7% when I hovered it down to 3.4volt...
    It jumped from 18% to 3% on the way down... it was out of wack...

    Your battery is new...
    My opinion... go fly and stay above 40% for today... still should get 12+ mins of fly time...
     
    #2 John Alan, Aug 30, 2015
    Last edited: Aug 30, 2015
  3. Mr Phantom

    Joined:
    Jun 19, 2015
    Messages:
    294
    Likes Received:
    25
    I guess you are correct, the battery has never been flown with and also I'm not sure if the calibration succeeded since it wasn't an uninterrupted discharge, so i guess i will fly it down to less than 5 percent and then charge it back to 100 percent.
    Maybe the battery needs to be put under load before its specs can be trusted?

    By the way, about my earlier statement that i read somebody said that when the battery is fully charged the individual cells have a voltage of 4,4 Volt, i just read another post here on the forum where "The Editor" said that a full charged cell voltage is 4,34 Volt. Just in case somebody wonder.

    Well i will do the battery calibration process again tomorrow, but this time i will do the discharging by hovering the aircraft instead of letting the battery sit in the aircraft for 4-5 hours.

    I´m still curious what the accepted difference between the individual cell voltages are? Thanks.
     
  4. The Editor

    The Editor Moderator
    Staff Member

    Joined:
    Aug 7, 2013
    Messages:
    6,722
    Likes Received:
    3,878
    Just to (hopefully) clarify things a little.
    All lipos internal resistance increases with age, its physics and a characteristic of the battery chemistry - you cannot escape it.
    As this internal resistance increases, the packs will not give up their charge so readily under load and the overall capacity of the battery will diminish.
    What the calibration procedure is doing is telling the fuel gauge (smart circuitry) what 'Zero' and what '100%' is. These two points actually change over time (which is why the health or status of the pack starts off from new at 100% and then goes down over time with decreasing mAh capacity).
    Regular battery calibration resets the monitoring 'end points' and means the battery level information is as accurate as it can be.
    Additionally, over time, since the internal resistance increases, the drop under load will change and the cells will take longer to recover or bounce back after that load is removed. You may notice a new pack only drops 0.5v or so during hover whereas an older pack could drop a volt or more!
    Part of CAA certification means we must keep battery logs and record every flight time we make and with what battery. Doing this means that if a pack is showing abnormal behavior a 'trend' should be spotted early on before any sort of failure occurs and that pack can be retired.
     
  5. SimonMW

    Joined:
    May 15, 2015
    Messages:
    103
    Likes Received:
    30
    Just to be a bit anal, the CAA regs are that we must keep an aircraft and pilot flight hours log to show currency, but there is no legal requirement for a battery log. This question was asked at my ground school and we were told it was good practice to keep one so that you can keep an eye on the battery behaviour even though the CAA won't ask to see one.
     
  6. The Editor

    The Editor Moderator
    Staff Member

    Joined:
    Aug 7, 2013
    Messages:
    6,722
    Likes Received:
    3,878
    Strictly speaking you are correct - However, I have it written into my ops manual that I keep a battery log (as well as the mandatory flight logs) so I have to keep it up :(.
     
  7. SimonMW

    Joined:
    May 15, 2015
    Messages:
    103
    Likes Received:
    30
    That's true. Though don't forget that the OM is for your organisation and how you want to work, so you are perfectly within your rights to remove the requirement for a battery log and instead check battery health with the DJI app. As long as you have access to that health info I doubt the CAA would object.
     
  8. barnesois

    Joined:
    Jul 5, 2015
    Messages:
    3
    Likes Received:
    0
    In the process of deep cycling my batteries (slow method, motors switched off, until the Inspire auto switches off). Just before it powered down one of my batteries (TB48 - flown once) had the attached cell voltages. After a full charge the spread was 4.30V - 4.34V. I'm running them down until auto shutdown (instead of down to 5% - as in the manual) based on advice on here.

    I have had the sudden voltage drop on a couple of my batteries - but not while airborne. A couple of batteries had been flown down to around 30%. When getting home later and checking them - they were critically low (around 5%). Hence the reason I am deep-cycling them now.

    Do I have anything to worry about?
     

    Attached Files:

  9. gregdd

    Joined:
    Jul 8, 2015
    Messages:
    240
    Likes Received:
    75
    I dont see anywhere in the DJI manual where it says continuous discharge when conditioning/calibrating the battery. Can someone confirm this is a DJI documented procedure or DJI recommendation. Or perhaps it is an observation from members?\