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Let's start posting dji assistant BATTERY data, HERE!

Discussion in 'Phantom 2 Vision + Discussion' started by yorlik, Jul 20, 2015.

  1. yorlik

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    dji says our p2v 5200mah batts are good for 300+ charge cycles.

    Imperative data from actual users say it is more like 20-50 cycles, with a few going 100+ but none reaching the rated 300 min spec.

    Since dji will not share REAL battery data with us, let us compile it ourselves!

    I propose that we each post here the full battery data assistance gives us - anytime we run the app and have time to post it here. With this data, we can build our own dji curves for these batteries.

    With this compiled data, we can state for sure what these batteries require as far as charge and discharge rates. This info alone should allow each of us to double our cycles.

    For instance, today, dji says "discharge every 20 cycles to 8%." This goes against all known lipo design data. Others are reporting that 80% discharge according to dji assistance is 3.70 volts - again, not very normal for this chemical make up battery, but true according to dji.

    I will post first from today's flight and 2nd battery charged a few days ago but not used:

    Proposed format:

    DATE:
    SN:
    CAPACITY:
    NOW:
    %LIFE:
    %NOW:
    CYCLES:
    FULL V:
    CELL1:
    CELL2:
    CELL3:
    TEMP:
    No. of 8% discharge cycles:
    Typical discharge level:


    DATE: 7/20/15
    SN: 5585
    CAPACITY: 5387
    NOW: 2563
    %LIFE: 93
    %NOW: 47
    CYCLES: 21
    FULL V: 11398
    CELL1: 3799
    CELL2: 3800
    CELL3: 3800
    TEMP: 36.9
    No. of 8% discharge cycles: 0
    Typical discharge level: 65%

    DATE: 7/20/15
    SN: 736
    CAPACITY: 5367
    NOW: 5364
    %LIFE: 93
    %NOW: 98
    CYCLES: 22
    FULL V: 12556
    CELL1: 4187
    CELL2: 4184
    CELL3: 4184
    TEMP: 26
    No. of 8% discharge cycles: 0
    Typical discharge level: 65%
     
  2. justin00

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    at work so can't check..
    but for now...

    2x batteries

    cycles: 165 on each

    Most people seem to have issues but mine have been good..

    only ran them down to 0% maybe 3 times... supposed to do it every 10 or 20 cycles if I recall ?
     
  3. basheer

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    I have two battery both last 23 cycle then both swelled maybe the reason I discharge them to 8% every time . I purchase new battery now I will always discharge to 30% and unplug directly from charger after fully charged and will how many cycle will new battery last
     
  4. yorlik

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    I would say chances are like 95% probably you killed these with all those discharges so low. I will comment that MY OPINION is that if you do as you propose with the new batteries, you will also prematurely kill them. There is nothing wrong with using them from 100% to 70% each time and leaving them like that unless you plan to not use them for a LONG time; then the recoomendation to drop them to 50% MAY have some validity (I don't agree with 50% either - I think it is too low), and the batt will do that for you anyway if you dont touch it for 10 days. Consider NOT discharging to 30% EVERYTIME.


    I have nicads that are 30 years old, nimh 10-15yrs old running just fine still in various pieces of equipment; I just have kept them charged and trickle charge them at about 2%. NOt same as lipo, but concept is the same - don't discharge them so deep so often. I may be all wet, but it seems to work for me so far.

    If you want to send me your two useless batteries, I would like to have them to test theories on why dji fail with so few charge cycles. PM me for my address if you want.
     
  5. Ironheart

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    What do you think is the best percent for "Long Term" storage?
     
  6. yorlik

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    i'm no expert. i just know that discharging down real low wears these out. it is said storing fully charged is bad too. i know i have made lipo cells stay like new for years with daily discharge to typically 60+%, then began killing them in months with higher discharge rates and levels..
     
  7. yorlik

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    So. No one sent me data on their batteries as reports by assistant, so I have had to use only my batts... ok... I now enough data to show a trend and make some comments.....

    Here is a chart of some of my data, showing cell voltage vs percent charge reported by dji, vs mah capacity.

    upload_2015-8-25_18-40-59.png

    Obviously the one blue point off the trend is bad data - maybe I wrote that point down wrong.

    But it is interesting to just stand back and look at this data......

    We all know that lipo batteries should have a curve like this:
    upload_2015-8-25_18-44-29.png
    One major key to making a lipo battery live a long life is to NEVER go over the sharp edge at end of charge point. In this example curve, 3.6vdc. Go past that you do irrepairable damage to the cell.

    No stand back and look at the perecent charge djii shows us in assitant, on our cell phone FPV, and on the smart battery lites.... THEY GO WAY OVER THE AVALANCHE POINT! Go there and you make your possibly 300 charge cycle battery live 20-75 as folks typically get!

    DISCHARGE TO 8% AND KILL IT EACH TIME TOO!

    OK, in dji defense, they are not battery experts. But when they get enough feedbck from customers that discharging to 8% each 20 cycles is killing the life of the batteries, you would think they would ask their batt supplier for comment! Perhaps they could change their docs to stop telling to do this!

    More data is needed to make better curves. I will get that data in another couple years myself if no one ever sends me data to compile here. OK. I will help MY batts last a lot longer by not going below 30-40% charge on them.

    Keep in mind this curve is for unloaded batts: the voltage droop under 5-10-20-30amp flying load is an easy 0.5v more! You can see that actually FLYING at less than 30% or so on the batt lites is killing your batt life.

    More data will refine this, but if you want to believe this data or not is up to you. My opinion is anyone discharging below 25-35% as shown by dji is prematurely killing their batteries. Both mine have spent their life above that level except for that one test here, and check it out: after more than 20 charge cycles they both show MORE capacity than 5200mah new. You decide.

    If you feel like sending YOUR batt data from dji assistant, I will add it to this to get better curve.
     
  8. yorlik

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    another thought: it looks like the knee of the curve happens at what dji calls about 45% level; after that, the dji seems to drop %charge indication very fast.

    Hmmm... this sounds familiar to what foks are seeing? batt lasts well down to 50%, 40%, then it can drop in very short time causing RTH or landing on low battery.... hmmmm...
     
  9. RichWest

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    I had a 25% battery last night drop to <10% just by lifting off. So I agree with your statement about falling off quickly after 50%. It's more related to the technology rather than DJI. We take for granted what the poly-lipo batteries bring to the table of RC flying. High energy and light weight.

    Regarding your previous post, DJI's suggestion to discharge to 8% ever 20... I agree that has been a mistake as well, but selling a proprietary battery is what makes money long term. Can DJI make them better, sure, but why at this point? No other RTF has better battery performance as of yet. This will be an important selling feature in the future, just like it did for the battery operated tools biz. If I offered you a RTF quad that was comparable at a 20% increased cost and that had a two year warranty on the hardware and batteries, would you buy it?

    FWIW, DJI is doing a couple of things regarding warranty and batteries... P3 and Inspire are now at 6 Months or 200 Times (Priority on minimal value). Whereas the P2 series is a three month warranty. http://www.dji.com/service/warranty-period. Funny, there's no warranty on the frame...
     
  10. jjfromaus

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    I would like to add my thoughts and info with regards to the DJI "smart battery" phenomena.

    First and foremost the DJI smart battery is meant to keep your craft in the air, thus any deviation from this smart battery's task or normal function, may lead to or trigger dire consequences to your flight and craft. It is the singular MOST IMPORTANT part of your craft and often the most neglected.

    DJI's smart battery is and will always be a Lithium Ion Polymer battery, thus it would be wise to say that all the science and data available regarding LiPo's apply to the DJI smart battery :

    1. LiPo's batteries have a definitive shelf life and they will deteriorate and become progressively worse as they become older, whether you use them or don't use them often.
    Some LiPo manufacturers typically warranty their batteries for a year. Certain manufacturers warranty their batteries for lesser period and in our case 3 months:oops:.

    Conclusions:
    a.) Make full use of your batteries within a 2 year period. Purchase only as many batteries as you require, as time ticks on they will self deteriorate!
    b.) Ensure you buy "freshly" manufactured batteries, a battery that has been on the shelf for say 3 months or more has already lost a marked life cycle capacity before its first use.
    I comment under correction, I have not seen DJI smart batteries with a manufactured date on them? As end users of DJI products, I would like to insist that DJI displays manufactured dates on their "smart" battery packs.
    c.) Avoid buying used batteries, as they could have been subjected to LiPo "torture" or have been lying around unused for extended periods thus prone to unknown circumstantial deterioration.
    d.) Store your LiPo's in a cool environment, heat is a LiPo killer.

    2. DJI recommends that their smart batteries are discharged to 8% every 20 cycles, I have questioned this practice with inconclusive and contradictory reasoning, however it seems that DJI has had reason to recommend this practice, albeit a very significant life cycle killer of the batteries. I would dare to say this practice is promoted due to several reasons, and one of them is evidence of the LiPo memory effect:eek: and a methodology of testing cell performance capability or defect detection.

    Okay I will probably be inundated with a barrage of comments from members disputing my statement, however it has been proved!
    LiPo's do acquire a memory according to Professor Petr Novak, Head of the Electrochemical Energy Storage Section article in Phys Org. (see attached reference).

    Could this DJI recommended practice be the reason to reduce or avoid un-explained crash behaviour of the craft, sudden loss of battery capacity during flight, fly- aways etc?
    The DJI smart batteries have a microprocessor chip controller that basically manages your smart battery and provides information to the DJI flight controller. Most LiPo manufacturers have a inter cell balancing charge connectors on their cell packs, DJI smart batteries does have this feature albeit self controlled - "smart".

    Conclusions:
    a.) One distinctive advantage of the DJI smart battery is that it self manages the charging and discharge of the cell pack, the inexperienced or "don't care" operators are "looked after" .... for a short while.
    b.) The most obvious disadvantage is that without the operators interference, individual cell condition observations during charging and balance charging, the reliance of the batteries health is subject to the "smart" capability of DJI's batteries. Earlier firmware did not have the ability to auto discharge a fully charged cell pack after a specified time, according to many fellow members observations and other forums documented experience. This would have led to many premature battery failures and craft crashes due to lack of adequate knowledge of LiPo battery technology.
    c.) Arguably many experienced LiPo technology end users insist that LiPo cell packs should be slowly charged and balanced to extend the life cycle of the LiPo cell packs. The most obvious and important of many reasons is heat build up within cell packs, non linear heat energy dissipation in cell pack sandwich construction.
    d.) Is there anyone on this forum that has tangible evidence of attaining 300 charge cycles on the smart batteries as per DJI claims? I consider the claim to be misleading and arguably misrepresentative of a DJI craft operating costs prior to purchasing their product, I have to admit I would have bought a DJI smart battery operated craft irrespective, but with a keener eye on smart battery life cycle preservation.

    3. Yorlik has a really good proposal to determine and analyse the actual attributes and behaviour of the DJI smart battery, the more battery data is acquired and analysed, the more we will have factual evidence of the smart battery capability, limitations and potential flaws.
    A comprehensive data logger that has the capability to log multiple specific smart battery operational values and onboard flight controller activity connected to the craft, would be the "Rosetta stone" of information on these smart batteries. Not only would the data be a valuable tool, it may determine and provide indicators of a future battery failure.

    I have attached a presentation that i have transcribed and translated with permission from Frank Siegert a forum member at RC Networks Germany, with some very interesting info and tips on LiPo cell technology, It has taken me some spare time to transcribe / translate, but i feel it was necessary to convey these facts regarding LiPo cell technology.

    I will endeavour to add to the pool of LiPo cell information at a later date as I expand my knowledge of LiPo technology.
    Happy reading and take special note on the tips of how to extend the life cycle of your LiPo battery.
     

    Attached Files:

  11. RichWest

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    You've made some good points @jjfromaus .

    "DJI recommends that their smart batteries are discharged to 8% every 20 cycles, I have questioned this practice with inconclusive and contradictory reasoning, however it seems that DJI has had reason to recommend this practice, albeit a very significant life cycle killer of the batteries. I would dare to say this practice is promoted due to several reasons, and one of them is evidence of the LiPo memory effect:eek: and a methodology of testing cell performance capability or defect detection."


    I agree with this assessment.

    I still believe DJI cares less whether the batteries perform beyond 3 months or in the current offering 6 months or 200 chargings. It's to their advantage for the long haul.
     
  12. yorlik

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    very interesting reads jjfromaus. Thanks for posting.

    The first one by the professor who says lithium batts have memory is talking about lithium-iron phosphate (LiFePO4) not Lipo chemistry, so not sure if his thoughts would even apply to our dji batteries.

    But I would have to take exception to his findings based on 3 years of very intense LiFePO4 100% Ev testing... I ran 35kwh, 118 cells, for these three years, normally using only 20-30% of total charge. At the end of 3 years, my cell voltages and kwh capacity was almost identical to new. I would normally only drive 20-30 miles per day per charge, out of total range for 100% capacity use of about 120 miles. I worked with the BMS charger engineers closely during some of this time, helping them correct and improve their balancing and reporting software. I also kept the batts 100% charged most off times. I have a real hard time believing this guy based on my experience. I also question why the other 300,000 battery experts do not agree with him? But we all might be wrong!

    I think dji's reasoning for the harmful deep discharge is an attempt to allow the3 sets of cells actually rebalance. They charge with 4 amps yet balance with a few milliamps; that means it really does not balance well at all. So they try to achieve better balancing by discharging them all deeply in the hope the higher energy cells will be low enough to allow this balancing to have an effect. Another reason to consider charging by rc specialized charger - at a lot lower rate! consider 100ma balance charge difference vs 4000ma charge: means the balancing can only charge a cell set at 2.5% less current the higher energy one! with 4 amps, the total charge time is only an hour or 2 at most, so the balancing is almost a laugh. Now charge at 200ma and walla! your balancing current can be 50% and get-r-done. This has alway been my pet peeve: my 100ah cells on my 118 cell EV had similar balance current difference; why I left it plugged in ALWAYS. We figured one day that if 1 cell needed balancing out of the 118 by say 10%, it would take 27 years of charge time (I charged at 30 amps)!

    Now your second article was really great on lipos! I am not a chemist so got a bit bored by all the chemistry, but found the last page GREAT! Since you posted it for all to see, I hope it is ok to just show that page here as I think we can all related to it, and I agree with their conclusions:

    upload_2015-8-27_19-23-40.png
    from LiPo Overview.pdf
     
  13. miket234

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    8/29
    Batt 2
    Ser. 1239
    Current capac. 5270
    % of life 94
    Current charge 97
    Discharge times 18
    Indiv. cell voltages keep changing...each around 4122

    Batt 1
    Ser. 2818
    Current capac. 4825
    % of life 92
    Current charge 97
    Discharge times 25
    Indiv cell volts in the 4130s
    On this battery, I just saw that I only have 3 blinking lights when doing the battery test, but the life is still above 90. Batteries were new in january...have deep discharged below 8% once.
     
  14. yorlik

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    thank you mike123.

    I added your points to the dji battery curve. I also spent 1.5 hours today charging a battery to fill in the blanks from previous 60-90% dji reported level:

    upload_2015-8-30_17-22-0.png

    I am trying to identify what dji thinks is % charge left vs std lipo voltage levels....

    It is appearing their % charge vs lipo actual volts is a bit off; I am SURE it not that their engineer was drinking heavily when he coded it into the smart battery, but I do not understand YET why they have the big drop off in reported % charge in the 90-50% range. This does not jive - yet - with how lipos work.

    I am just trying to identify why some folks get this commonly reported "I was at 60% charge and all of a sudden it dropped to 20% and autolanded out in the field and I lost it...." It APPEARS on the surface that perhaps that engineer maybe WAS drinking that day he coded the curve?

    dji-dave - would you be willing to ASK about this for us?

    Perhaps I do not have enough data yet to make the real dji curve at both ends? It MAY be that great dip is ok but just at wrong point, and they really are keeping us above the killer low voltage knee... I do not have enough data yet to say for sure...

    I know of NO lipo battery curves that have such a knee from 90 to 60%: the chemical makup puts the knee below 25%...

    Please send YOUR battery data and I will add it to this curve so we can all understand better what the telemetry is telling us.
     
  15. kirk2579

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    Screenshot (1).png Screenshot (1).png Screenshot (2).png


    sorry for extra image

    have a 3rd dji
    full 5106
    current 5037
    % 98 charge
    life 92%
    discharge 26
    sn 3026
    4195
    4165
    4175
     
  16. yorlik

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    thanks Kirk. will include in next curve update!
     
  17. RichWest

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    If the voltage drops on the battery, the bird requires more throttle to maintain same as full i.e. at higher voltage. So possible this is that the % results are faster on the bottom (lower voltage) rather than the top.....due to faster drain on battery.

    I applaud your effort to understand, but in the end it's a gauge for remainder. I look at it like a fuel gauge on a car, when topped off it seems like forever before it falls below full and then it's a race to empty. Some people wait for the warning light to let them know 25 miles to empty and others pull off as soon as they hit a 1/4 of a tank.
     
    yorlik likes this.
  18. yorlik

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    so I have 38 data points now of %charge/voltage/mah - as reported by dji assitant - to make the dji 5200mah batt curve more accurate:

    upload_2015-9-8_15-47-11.png

    It APPEARS when we get down to 40% charge that the %charge nose dives quickly. We really need more data points from folks filling this area in.

    What this seems to be telling us is the %charge left as indicated by batt and assistant is usable and good down to 40%. 40% of 5200 is 2000mah left. But something is missing in this description because it appears that last 2000mah is not really usable before the battery just dies FAST. This point on the battery curve should be about 10% left, not 40%. It should happen at 10% of 5200 or 520mah left, not this huge 2000mah left according to dji... I can't wrap my head around what is happening without more data. I refuse to run my good batteries down in this area so need data from others who have inadvertently or routinely DO run down to 30,20,10%.

    Still keeps pointing to you take your chances of a batt failure or autoland or batt dropping in seconds if you fly below about 40% left!

    consider sending your assistant data ($charge, batt voltage, & mah now) if you plug into assistant and capture a charge less than 40%.
     
  19. kirk2579

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    I seldom ever go below 50% anymore. Mostly about 8 to 12 minutes then land. Always swap batteries before retake off.
    I choose shorter flights vs loosing my quad to low battery issues
     
  20. RichWest

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    I found an interesting write up and thought I would share it with you, may provide further details as to why the voltage appears to not register correctly. Voltage Failure Modes - Battery Education

    Recently I was reminded of an issue called surface charge on some high end lead acid gel batteries I work with. The batteries would fail during operation, but still showed a voltage within acceptable range of 27-23.4 VDC as far as the electronic monitors were concerned. Problem was if you didn't load the batteries, resistive load, while measuring voltage you'd get a false reading while testing. The devices I run have a 130A momentary peak draw, run is about 23A 18A...a cycle is complete within 1.5 seconds. We now load test with an inline resistor, which has reduced our in service failures to about 0.1% over a 5 year field life. This was done about 15 years ago, so hadn't worried about issue in testing batteries.

    Also I'm experiencing indication of battery failure with my #2 battery. Out flying over the last weekend and had a rapid voltage drop 30% to 8%. I was on my return to home, with plenty of time to spare, and on descent the bird started a rapid descent. Looked down at the battery % and it was at 8%. I understand the descent rate and why, low voltage = low motor output.
     
    #20 RichWest, Sep 11, 2015
    Last edited: Sep 11, 2015