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Battery charged 20 times. So now discharge to 8% or 3%?

Discussion in 'Pro/Adv Discussion' started by Sotiris Boutsis, Jan 13, 2016.

  1. Sotiris Boutsis

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    DJI suggests to discharge down to 8% after 20 charges to balance the cells. There are some posts here and there saying that after the new firmware the batteries should be discharged down to 3% but there is nowhere posted officially from DJI. There are also some voices saying not to discharge that low as this is killing the cells instead.

    So what are you guys suggest to do? 8%, 3% or nothing?
     
  2. msinger

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    This is not necessary.
     
  3. Sotiris Boutsis

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    Thanks for the quick reply. You mean not necessary to discharge them at all or not necessary to discharge them down to 3%? I should do as the manual says and discharge them to 8% only?
     
  4. msinger

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    AG Drone Works likes this.
  5. Sotiris Boutsis

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  6. AlexSP

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    If you go to 3% that could harm the cells permanently. I for myself don´t even go bellow 20% or 3.0V per cell. Ever.
     
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  7. Sotiris Boutsis

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    I know what you mean but I think since the manual says so down to 8% with no load in the motors should be OK.
     
  8. bbfpv

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    Manual says down to 8% or until the battery shuts off, which I'm guessing implies they shut off pretty close to 8% so as to not harm the cells.
     
  9. Spydertoph

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    I'm still learning about LiPO batteries, but I know with the AGM batteries I use in my racecars, if you drain them down that far more than a few times they simply won't hold a charge. I've accidentally killed 3 batteries now, by forgetting to hook up the tender during storage in the off season.

    LiPO's act a bit different, but there are loose correlations to be made.

    Voltage is a very important variable in LiPO batteries. The lower the starting voltage during the charge phase of a LiPO the more potential for damage. The lower the voltage, the higher the internal resistance the battery has (talking about charging). It's my understanding that anything below (or around, arguably) 3.0v you will see permanent increase in internal resistance in the battery. This creates excess heat when charging and a potentially dangerous situation with thermal runaway. It's my understanding, that the lower the cell voltage the slower the battery must be charged, to avoid thermal buildup and a runaway situation. I don't know how smart the dji charger is, but I'm guessing not that smart?

    It's my practice and recommendation to never let a LiPO battery cell voltage fall below 3.00v. Like I said, I'm still learning, but that's what I've gathered so far.

    Happy flying!
     
  10. msinger

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    DJI smart batteries shut off when the first battery cell reaches 3.0V.
     
  11. Spydertoph

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    Nice. Do you know if the charger modulates the rate of charge to the battery based on the current (lol) voltage status of the battery?
     
  12. msinger

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    I don't know the down and dirty details of how the charger works. Sorry :(
     
  13. Spydertoph

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    No worries, neither do I, haha. :)

    I'm just curious.
     
  14. AlexSP

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    From what I could gather so far, the smart batteries are not much different from other smart core systems used in different appliances (like the ones from Lupine Lights for instance - top stuff btw). Basically, they control the charge and discharge parameters to keep the battery in a certain condition, avoiding deep discharges and overcharges. They must have some kind of management and measuring/reading systems as well, to interact with both the P3 energy control and the app display.

    Charging and discharging must be controlled in accordance to battery/cell specs, also considering the whole energy demand parameters of the AC. So a system must be used either on the charger, battery or the AC to control the discharge, and in the battery or charger to control charge, to keep things right. Both are important, as both can damage the battery if done wrong. Those are rather simple stuff really.

    DJI put the smartness (so to speak) in the battery, I'd guess for both economical, manufacturing and customer care reasons. Even though that means one smart core for each battery, it's more simple and easier (I'd add "safer" as well) to use, from the customer's side. And that seems to be one of main DJI's targets. But I doubt they have any sophisticated feature on them such as cell balancing capacity or stuff like that. Heck, that would mean serious electronics. I own a couple of really smart and advanced chargers, you need to access the individual cell taps and all to perform that... Anyway...

    So, smart systems used in chargers can be more sophisticated and thus more expensive. And it'd be necessary a second smart system on the AC anyway, or else the pilots would have to time the flights more precisely and measure voltage right after landing to get accurate readings on capacity and state, just like we do with RC copters, planes, cars, etc. So having only one on the battery itself covers a lot of bases. But it's certainly more basic than one found in some chargers, that's for sure. Maybe that's why DJI recommends a "deep discharge" (8%), to sort of calibrate the smart system and get more accurate readings (percentage and voltage) after a few cycles.

    That's all fine and dandy, hobbyists use a voltmeter and some simple math right after flight to get accurate charge/capacity of LiPos all the time. I still do with the DJI battery so I don't really see much of a point in performing the deep discharge. I'm yet to compare the readings on the app and battery to my "manual" readings but I suspect it must be within acceptable margin. if it doesn't, then I'll do the deep discharge and see what gives. I sure doesn't hurt much, if done every 20 or so cycles I guess it's fine.

    Also, I'm pretty sure they wanted to keep everything into a "closed system", pretty much like Apple. That makes sense from the economical/business perspective (they sure make a heck of a lot of $ from batteries, the margin must be big on those); increases the overall quad safety (debatable, but likely); and allows them to keep the whole quad within desired parameters of operation, by avoiding "third party" solutions, mods, improvisations, etc.. And the overall P3 design gets cleaner and more streamlined as well.

    Dealing with "dumb" LiPos is a nightmare, even experienced RC hobbyists screw a battery or two every once in a while. If you have a few dozen ones - and different ones too, laying around and being used all the time for different applications, which is quite common in RC... Well, it's something that I'd guess the majority of P3 customers would hate, it'd be a real turn down for many.
     
    #14 AlexSP, Jan 13, 2016
    Last edited: Jan 13, 2016
  15. Sotiris Boutsis

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    Alex great analysis thanks. I am an old RC helicopter pilot and I still remember the days with the bulky NiCads and the chicken dance a brand new Xcell Stratus did because of a shorted Lipo:(
     
  16. dr.evil

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    very true. other thing that also kills the battery is to top it up and not use it within a reasonable time frame.I guess because of internal pressure from anode dilatation. I've set my batteries discharge time to 10 days like DJI set it, fly them never under 35% and TOP THEM UP before I'm sure I'll fly them that day. Hunters don't load live ammo in the rifles when they get back home. LiPO manufacturers ship all lipos half charged and never full. The battery equilibrium is around 3.85 volt per cell, at this voltage the battery should discharge at a rate of 1% per month, that unless the inner sensor and management circuitry draws too much.
     
    #16 dr.evil, Jan 13, 2016
    Last edited: Jan 13, 2016
  17. AlexSP

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    NiCads??? Ahhhhhhhhhhhghhhh :confused:

    LOL :D

    Yeah, I do a lot of night biking since the 90's and it was crazy to deal with the battery technology of that time. Not to mention the weight, and it was very, very unreliable even when dealt with carefuly. Things are much, much easier now, can't even begin to compare! Now I can go out with a small LiPo strapped to my stem and power up a 1300 lumen LED light smaller than a swiss army knife... for hours... without fear of being in the dark in the middle of nowhere...

    Same with my copters, quads, cars, etc.

    And maybe that's why I still take good care and all but don't obsess too much about it. What I got from the LiPo early times is this: avoid heat in general; avoid cold during use; avoid overcharge and deep discharges; avoid "eating" through the cycles by obsessing with top charges and storage levels all the time (unless of course for longer periods)... basic stuff like that. Otherwise, it's the LiPos serving me and not me becoming their slave :p
     
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  18. AlexSP

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    In my experience even though that's indeed not good for LiPos it doesn't really kill them. That's the overall recommendation for LiPos yes, and DJI and other manufacturers of appliances that use LiPo batteries have that on the manual to make up for pilots and users that take really long and frequent breaks, or aren't used to deal with LiPos and quads, so they won't ruin their batteries in the short term. If you store your battery at 100% for a week or 10 days every once in a while t's OK, IMHO there's no need to keep discharging them to 30 or 50% every week.

    If I have no flights on the lineup I just leave them as they are (always above 30%). But if I topped my batteries as preparation for flights that for some reason didn't take place, I'm OK leaving them at 100% for a week or even a few days more. If I know for sure won't be flying for two weeks or longer then I'll bring them to ˜50% regardless of their actual charge, alright. Otherwise I just store them in the case or the wine fridge inside a plastic bag and leave it at that.

    Also I've found out that if you fly frequently then it's OK to take off with a battery at ˜97% or thereabouts. I do that all the time, with all my toys, and I prefer to do that than keep cycling through the battery all the time just to keep it at 60% for storage, or at 100% for immediate flights. LiPos have limited cycles, each one counts and I'd rather use them partially than waste any. Likewise, if I do 2 or 3 short flights in sequence (say, within a couple hours or something) I'll do them all on one charge, until it reaches ˜30% or ˜3.6V per cell.

    Of course that's what I and most of RC mates do, I'm just sharing my experience here. I advise others to follow the manual or do as they feel better.
     
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  19. Mark The Droner

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    There are a lot of threads on this. They are all pretty much the same. Some say don't do it. Some say do it. Some say follow the manual. Some say the manual is wrong. Some say the engineers at DJI are smarter than we are. Some say the battery experts are smarter than the engineers. Etc., etc.

    The P2V and P2V+ manual states the battery should be deep discharged to "below 8%" which is to say it could be 3% since 3% is below 8%. My deep discharger device discharges until the battery turns itself off, which is at 3%. The battery should be fully charged immediately after the deep discharge. I haven't had any issues.

    I believe the P3 manual states the battery should be deep discharged "to 8%", which is different than the P2.

    There seem to be good reasons to do the deep discharge, but others disagree.

    I suggest you search for threads such as this one and just read up and then make your own decision.