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Problem increasing air time by lowering low voltage cutoff

Discussion in 'General Discussion' started by jinspin, Sep 28, 2013.

  1. jinspin

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    I lowered the 1st and 2nd level default low voltage alarm in naza to

    1st level 11.1 .6
    2nd level 11.0 .6

    With 2200 3S Phantom lipo i got around extra minute from 5:30 to 6:30 which was great with my gopro gimbal and prop guards.

    I checked voltage and it says I discharged 2200 phantom lipo down to 11.1v or 3.69-3.7 per cell which everyone says is acceptable cutoff. I tried another running battery and it discharged to 3.67 per cell or 11.03.

    But then I have seen a lot of posts where it says to follow 80% rule and not to put more than 80% back into battery. So when I charged the lipo back up - it actually put 2059 into battery which is more than 80% and is about 93%.

    I am getting discrepency between acceptable cell voltage 3.7v but then it seems to violates 80% rule.

    So this is not good for battery because I am putting more than 80% back into battery? And I should raise back the low voltage cutoffs? It was great having more air time but I don't want to ruin the (costly) battery.
     
  2. Skylane765

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    Re: Problem increasing air time by lowering low voltage cuto

    I have my first warning set at 11.2 with .40 diff so the right column 10.4
    2nd is set at 11.1 .80 load 10.3 on the right.

    So the way mine is set, it makes the 80% rule. Remember the load v is what triggers the warning, that is the number on the right at load voltage.
     
  3. Skylane765

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    Re: Problem increasing air time by lowering low voltage cuto

    The 3.7 works with the 80% rule
     
  4. jinspin

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    Re: Problem increasing air time by lowering low voltage cuto

    Thats what is confusing. I get really close to 3.7v but then i have to charge up to 93% instead of 80%.
     
  5. Skylane765

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    Re: Problem increasing air time by lowering low voltage cuto

    Do not confuse loaded voltage, that is only to alert you what voltage will be unloaded. It is the resting voltage that you do not want below the 80%. But you can not ever see that 3.7 under a load, it will be lower with it in flight. You can have 3.7 resting with 3.0 under a load and still be ok. That is why you put the load drop to know when the phantom will alert you.

    DJI does not explain that, I had to figure that out, all loaded voltage will change based on the load your phantom is at. A phantom with a gimbal may have as much as 1.0 volt drop. A light phantom may have only .15 drop.
     
  6. Skylane765

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    Re: Problem increasing air time by lowering low voltage cuto

    DJI does tell you how to set the drop. I used a $2 voyage display hooked to the the balance lead. While flying under load I see what the loaded voltage is and then shut down and do it until I have 11.2 resting voltage at shut down and compare to loaded voltage on the display chip.

    My phantom is set with .80 v drop and have GoPro, GoPro case, and Garmin GTU10, so if more weight then it would be more that .80 volt drop.

    The 80% is not the charge. You charge to 100%. Do not discharge while flying below 80%.
     
  7. rilot

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    Re: Problem increasing air time by lowering low voltage cuto

    The 80% rule is kind of old. I'm not sure why it's still kicking around as the de facto limit. It appeared when LiPos were very new. These days I discharge to 90%+ and my LiPos are fine.

    However, it leaves less room for error if you find yourself further away then you thought when your warnings go off.
     
  8. marcus_canada

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    Re: Problem increasing air time by lowering low voltage cuto

    I agree, I've been using Lipos since Day One when nearly every other Lipo would crap itself inexplicably. These days I don't worry if I run them past 90%. The other day I got caught out and brought my Wookong-M UAP in under flashing Reds, I managed to get 5200mah into that 5000 battery ! What's that, 105% discharge? LMAO
     
  9. jinspin

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    Re: Problem increasing air time by lowering low voltage cuto

    That is good to know that putting 93% charge back in won't mess up battery.
    After some more testing I have my final voltage 1st level protection loaded 10.5 and 2nd level loaded 10.2
    I got 1 extra minute flying before 1st red light comes on from 5:30 to 6:30 which I am happy with.

    This way I got at least 30 seconds bring it back without damaging battery with around 3.7v cell and 1 minute before 2nd level hits and it starts to descend at 7:30. As people have said it is better to ruin a battery then to lose a quad.
    Thanks for all help.
     
  10. Skylane765

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    Re: Problem increasing air time by lowering low voltage cuto

    The 80% rule is the amount left in when discharged. If you run pasts 80% it would be 70 60 50%. At 90% that is not much of a discharge. Yes you can discharge more than 80% with no problem even down to 70%. It will not hurt anything. The 80% is just the rule to have the battery last longer and get more charges out of them. You can not discharge a battery 90% of peak charge and get a lot of charges out of it. Some chargers will not even start a charge with it that low.
     
  11. Skylane765

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    Re: Problem increasing air time by lowering low voltage cuto

    you can charge the lipo to 100% charge and be ok. I charge my battery to 99 100% every time I charge them. It is the the over discharge that you do not want to do. I think that is what confuses people.

    This will explain the 80% rule. http://www.rchelicopterfun.com/rc-lipo-batteries.html

    "A very good rule to follow here is the "80% rule". This simply means that you should never discharge a LiPo pack down past 80% of it's capacity to be safe. For example, if you have a 2000 mAh LiPo pack, you should never draw more than 1600 mAh out of the pack (80% x 2000). This is assuming a healthy pack as well that has the full 2000 mAh capacity (as packs age, their capacity drops)."

    "If you don't have a computerized charger to confirm the amount of capacity, another good indicator is to measure the open circuit voltage (no load voltage) of the pack or individual cells right after a flight/drive with a digital volt meter or other similar digital voltage measuring device. An 80% discharged LiPo cell, will give an approximate open circuit voltage of 3.72 to 3.74 volts. A 3S LiPo pack therefore would show about 11.2 volts after a flight when it's about 80% discharged, a 6S pack would be in the 22.4 volt region. The longer you wait after the flight/drive, the less accurate this voltage method of determining an 80% percent discharge works because as the pack rests after the flight, the resting open circuit voltage will increase slightly, perhaps up to 3.76 volts or so."
     
  12. jinspin

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    Re: Problem increasing air time by lowering low voltage cuto

    When I say I am getting 93% I mean there is only 7% left in battery and I am charging putting back 93% or 2046mAh back into the 2200 battery. This is when I am reading the cells to be around 3.7v.
    The 80% rule sounds like there is suppose to be 20% left in battery and you are NOT suppose to put back more than 80% or 1760 mAh back into battery.
     
  13. Skylane765

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    Re: Problem increasing air time by lowering low voltage cuto

    so you are referring to 7% as the rated charge and not the total voltage. I charge to 100% so my battery after use is 11.18 to 11.20. After charge it will be 12.6. And the charger shows about 2100 2180 ma back in, but that starts to go down the older the battery gets. I try to get 100% or 2200 out of my battery and that stays in the 80% rule that I think it should be.
     
  14. Skylane765

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    Re: Problem increasing air time by lowering low voltage cuto

    The way I see the 80% is the 3.71 per cell volt and after flying it is 11.2 that's what I do and set. The way the tech says is to only put 80% of a rated charge in. I do more like 90 to 100%

    When I check my battery after flying with the EOS Sentry it shows 11.20 v 20% so 80% was used. My warning is set there, but I can go longer if I need to and land when 11.10 .
     
  15. jinspin

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    Re: Problem increasing air time by lowering low voltage cuto

    I just did couple more charges and I am putting back into battery around 85% now.

    I also tried pushing one battery with air time to 7:30 from normal 6:30 air time on 2200 battery and voltage went down to 10.6v and cell voltages were all over place and unbalanced like 3.52 3.55 3.58. I can see that it was messing up battery. But it looks likes charger is balance charging it ok.
     
  16. Skylane765

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    Re: Problem increasing air time by lowering low voltage cuto

    I just looked and I have .40 loss not .80 I first said. It all depends on the load at what that is set at.

    Below 11.0 v many times may shorten battery life, once in awhile you will be ok.
     
  17. MrMediaGuy

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    Re: Problem increasing air time by lowering low voltage cuto

    My drop with Zenmuse, OSD, and Immersion VTX is 0.80-0.85V. Strongly recommend following the procedure in NAZA Assistant on the Voltage tab for how to determine the correct voltage drop (Loss) for your particular configuration. I got about another 2 minutes of safe flying time that way. Turns out I was getting the first-level warning way too early with the stock settings, when I had only taken maybe 1200mAh out of a pack instead of 1750mAh or so, which would be 80% of a healthy pack.
     
  18. mikrob

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    Re: Problem increasing air time by lowering low voltage cuto

    When I found my flyaway Phantom the battery was less than 9 volts & read 0% capacity on my tester. It charged back up to 98% capacity & has been fine ever since.
     
  19. Skylane765

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    Re: Problem increasing air time by lowering low voltage cuto

    Yes, the stock setting are to high for cut off.
     
  20. Skylane765

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    Re: Problem increasing air time by lowering low voltage cuto

    oh yes, you can go below the 20% it is just you do not want to go below 10% every time.