Mike-the-cat
Second Officer
Flight distance : 22488593 ft
Singapore
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DECinHSV Posted at 2017-4-16 22:18
Mike . . . curious why do you land with 25% left? Why not 40 or 50%? I often (majority of the time) land at 10-12% power. Sure its only a few min's more flight time per battery set and I do position the aircraft closer to me as it gets near 20-25% OR place in an open area so that the critical stage could do its thing if need be, but not sure I really see the logic of 25+ %. Interested in hearing why 25 and not 40+???
I use 25% as a benchmark for long flights to set a margin of safety. In some of my flights, I go out quite far (3.5km) and when you factor in wind, battery drain can be higher in the last minutes of flight. As you know, with all batteries, the ability to deliver current is diminished as the battery closes in the low end of state-of-charge. The behaviour is non-linear and can be quite scary. I know that some people have the ethos of getting into trouble and then finding excuses to blame someone else. I'm conservative and not ashamed to be.
As someone who has over 800 flights and now flown over 2100 kilometres, I have been in situations where, getting home was hair raising. At 15%, if there is a +/- 5% error in SOC evaluation by coulomb counting (which is how these smart batteries work), you run the risk of crashing an expensive craft. As I state to the next poster, this is fine if you know what you are doing. But I wont take the risk. Case in point: http://forum.dji.com/thread-93004-1-1.html
LiPo s do not 'like' being left at full charge for long and one should not drain them to their minimum operating capacity too often either. (this is recommended periodically for SOC calibration). If you discharge an Inspire 1 battery to 25%, where I am, the battery temp goes to 59-61C which is pretty toasty. And high heat is not good for batteries.
As for stopping at 40%, well, you are not using the full capacity of the battery, so that doesn't make sense although some say that to extend battery life, it may be a good idea to discharge down to different levels occassionally. I'm not sure about this advice.
The fact that DJI sets the default warning at 15% now, suggests that they have done some additional testing and feel comfortable with that mark. I'm probably being too conservative because I do note that the battery temp is about 5-7C lower for the I2 compared to the I1 at 25% remaining charge. This suggests greater resilience to current draw at that SOC for the I2, but why risk a $8000 craft?
I've read http://batteryuniversity.com/lea ... ium_based_batteries and recommend it as a reference
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