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More Battery wows

Discussion in 'Phantom 2 Vision + Discussion' started by Frank Ross, Sep 21, 2016.

  1. Frank Ross

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    I am fairly new to this hobby. Today a flew my P2V+ which I purchased used. After approximately 5 minutes or so I got the low battery signal and the P2V+ came home and landed. This evening I decided to put the P2V+ on "Assistant" and check the battery, only one LED lit and it was blinking. Assistant said Design Capacity: 5200, Full Charge Capacity: 4400, Current Capacity: 3820 and Percentage of Charge 7%. After fooling with Assistant for a while I turned the battery off and back on. Now 3 LEDs lit steady and Assistant read Percentage of Charge: 69%. Anyone have an idea?
     
  2. phxbird57

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    was the battery fully charged before you flew? Assistant is only going off of what the battery tells it. Put a full charge on the battery and check it again and I would watch that battery maybe going bad.
     
  3. Frank Ross

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    Yes, the battery was fully charged, I did a recycle on it by taking it down to 8% and doing a full charge. I checked it this morning and still three LEDs lit. I think I will take it out in the backyard and see if I can run it down. Perhaps it was a false reading of 8% when I performed the recycle.
     
  4. yorlik

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    Frank, Your battery may be fine but just the BMS is out of sync. You need to try taking it down, but the "down to 8%" is WRONG: depending on how far out of sync the BMS is, going down to 8% MAY fix it, but no guarantee.

    The correct wording should have been "take it down to 7%." I think it was typical Chinese manual language conversion error.

    Small change, but proved many times. What often happens is it will get to 8% but then folks shut it off - but but but that is where it often BEGINS the recalibration! So it will stay at 8% value whiile the battery voltage continues to drop to the calibration point (IIRC 3.7v avg/cell).

    So do as you suggest, or better yet, just plug it into assistance and watch % charge and actual battery voltage.... from your description you will see it hit 8% charge yet the voltage will be way higher than 3,7*3=11.1v... watch in amazement when calibration kicks in... 8% will remain but voltage will continue down - UNTIL t hits 6-7% at around 11.0-11.1 volts! NOW it is calibrated. Shut it off and go recharge and fly.

    Or do both; assuming you have fully charged battery in reality, fly it down safely, then put on assitant. assistant draws 1 amp while running, so it would take 5 hours to discharge a fully charged batt on assistant alone.

    If you want to see more of the science behind this, go here:

    Let's start posting dji assistant BATTERY data, HERE!
     
  5. Frank Ross

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    Yourlik,
    I ran the battery down like you suggested. although I only had it two feet off the ground it started to come home and land. Vision said there was quite a bit of battery left (24%) so I restarted the motors and ran it down to 0%. I then went in the house and the Phantom would still start. I ran it just a few minutes without the props and it stopped. Assistant said charge was 0%. It is now on charge and I hope to be able to fly tomorrow to see how the battery does. I think the battery is good. It sure took a long time to discharge with the props turning and the throttle set to almost let the Phantom take off. Thanks for the help.

    Frank
     
  6. yorlik

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    Hope it proves better for you. Guess I should have also said "don't ever run your battery down to 0%"

    I assumed my comment run it down to your 8%, watch it sit there not moving the % yet the voltage is still going down, and then AS SOON AS 8% BEGINS TO DROP, YOUR DONE - SHUT IT OFF.

    Sorry for the confusion. Going down to 0% is typically a really bad thing for lipos: but in our case what dji calls 0% charge left is really like 10+% in the real world - just don't tell anyone that. So it does no SIGNIFICANT harm, but just the same, don't go to 0% ever if you can help it. That one move may have reduced your already degraded 5200mah that was 4444mah yesterday to 4430 today... Not a lot, but why give any?
     
  7. Frank Ross

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    I read to not let the cell voltage go below 3.0 volts. The lowest cell was above 3.0volts. I've been told they are like NiCads and a cell can reverse. It is almost a full charge now. Thanks again.

    Frank
     
  8. yorlik

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    Please do let us know a couple things when you are done. Like did it get back to 100% on the charge display? What is the capacity NOW (was 4444 or something)? Did it run 10 minutes or so in the air from 100% down to 25% or so?

    For reference, if you only use it from 100% down to like 50-60% each time, then leave there until next use and charge it back up THEN just before use (ie., do not store at other than around 50%), you should get about 4x the life everyone else, who runs theirs down to 15-20% everytime) gets. Your choice as to which is more important to you...
     
  9. Frank Ross

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  10. Frank Ross

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    yorlik,

    I flew the other day and the battery did almost the same thing, it flew until it said about 6 minutes left then dropped to where it wanted to fly home. I was hovering close to home in anticipation of this happening. When I check the battery at home it was saying 7% left. I ran the battery down a little more and it never moved off of 7%. I charged the battery and it came up to a charge of 5024 mAhs. Each time I charge the battery the full charge mAhs goes up. It started at 4400 then went to 4800 and now 5024. I am going to keep fooling with this battery to see if I can get it to be reliable. I don't want to have to run down when the Phantom is too far out to make it home.

    Thanks for you help and advice.

    Frank
     
  11. yorlik

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    GREAT feedback for all of us! THANKS!

    I highlighted above; keep in mind the recalibrate routine MUST go at least 1 digit down from where it is "stuck" to actually recalibrate properly and fully... So by NOT letting it drop to 6% you stopped the recalibrate before it was finished! I tried to say earlier don't just let it go to 6 then all the way to 0... but DO make it go at least 1 digit BEYOND where it sticks without changing while the voltage keeps dropping - THAT is calibrating.

    An indication that a dji P2 batt has a calibration issue when it flies well from 100% down to 60 or 50 or 40 or 30 or 20% then all of a sudden in SECONDS drops to the magical 8% number. So shut if off there and it stays uncalibrated: let it keep going down for 1,2,3,4,5 minutes more "stuck" at 8 or 7%, and as soon as it begins to move again, BAM! you recalibrated it. Turn it off.

    Please let us know more!
     
  12. Mark The Droner

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    For the record, the P2V manual says to deep discharge "below 8%" which means dropping it down to 8% is inadequate. (It also says "... or until the battery won't turn on" paraphrasing). Other manuals for later aircrafts have said "to 8%" which is different than "below 8%" and I think is likely incorrect due to the language problem.

    I had an aftermarket battery last winter that became pretty severely unbalanced after having used it. I checked it at that time because it was acting weird, but I didn't write down how off balance it was at that time. I fully charged it and it showed the lowest cell was off by 81 mv. I thought that was too much, so even though the battery had only 19 cycles (not yet 20), I did a deep discharge all the way down to 3% using the device sold on eBay. I check it. One of the cells was 378 mv out of balance. So then I brought it back up to 100% and it then showed the cell out of balance by 71 mv. Still just a tad high but maybe ok.

    So I flew again and landed at 53%. Checked it. Lowest cell was off by only 38 mv. So I figured it was repaired. This was last January.

    But during all these procedures, the mAh dropped little by little. The last mAh reading in January was down to 5104 mAh Full Capacity from what was originally a 5400 mAh battery. I lose mAh on every deep discharge.

    A couple weeks ago I was again out of balance - it was about 200 mv out of balance at full charge. So did the deep discharge. Down to 3% and up. It brought the balance to 100 mv. Better but not good enough. But I lost 100 mAh! Now my mAh was down to 4985. So I did another deep discharge to 3% for balance and back up. It did nothing to balance it at all - still 100 mv off. But I lost another 100 mAh and am now down to 4885!

    I retired the battery. I'll use it for kitchen table stuff.

    What I don't quite get is why I lose mAh on every deep discharge, when the OP seems to gain mAh. Too many variables to figure it out. Maybe a crummy manufacturer? Maybe 3% is too much?