What else would the app use beside distance from the home point and voltage to determine the percent of battery left?
Best battery discharge method?
- Thread starter davey1der
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A lot- voltage alone is absolutely not relied on in determining available flight time. The value reported by the fuel gauging algorithm in the battery SOC is. Soecufically time to empty. And as I have said a lot of factors inform the algorithm including temperature, instantaneous and average current, battery internal resistance, lifetime health value etc. voltage tables and coulomb counting schemes are old tech.
You are completely guessing at what information DJI's software uses to determine flight time ("voltage tables"? Yeah.. I'm not buying half of that and.... voltage tables sounds like it has something to do with... voltage). What we do know is that it at least uses distance from home point and volts. I would not doubt that it uses more information but anything past that is a guess/speculation.
Using amps determines the draw on the battery but I say that this would be a very low level in determining flight time. You could be at full throttle and the amp draw would be huge. If amps were a major determination, flight time would be greatly reduced. But as soon as you went into a hover, amps would drop and the flight time would be greatly increased. That would make the percentage almost worthless.
Battery temps should lower volts more quickly. Same is true of most other things.
So I have no doubt that additional factors are used (but we don't know what they are or to what extent) but I'd say that voltage and distance from home point are the two most important factors.
I'm not saying people should ignore the percentage reading. What I'm saying is that people should also turn on and monitor the voltage reading as it can give more detailed information.
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Are you seriously suggesting that DJI might go to the trouble and expense of incorporating advanced battery management SOC’s in their products only to then not benefit from their features? That they might simply take the voltage and % remaining data from the SOC? That is a ridiculous assumption. I don’t think they could possibly be that silly. Luckily it is apparent that they aren’t. The fact that the remaining flight time depicted in GO is demonstrated to be as accurate as it is and so effective in accounting for actual flight conditions and battery health demonstrates simple voltage measurement alone is not the scheme employed.
There is no question that the difference between individual cell voltages (call balance) can be very important. I agree we should be paying attention to it. The fact remains however that monitoring overall battery voltage in flight is significantly less reliable and accurate in determining remaining capacity than observing the reported battery % and estimated remaining flight time.
Distance from home point (or specifically the estimated time to return to home) obviously is and must be a factor. The other important factor is the estimated remaining flight time determined by the battery management SOC (time until empty), voltage being only one of many factors that contribute to its estimation.
Of course voltage tables relate to voltage. Cell voltage has been used to estimate the state of charge of battery cells for a long time, well before LiION cells were available. The concept is a simple one, voltage indicates state of charge which, for a known cell capacity and cell chemistry, will allow remaining charge to be estimated. Its application is simple to implement, a “voltage table” is created by terminating the cell with a precision dummy load and measuring and plotting cell voltages during cell discharge against cell capacity minus Ah delivered. The limitations of this scheme are well known. Cell temperature, current demanded by the load and cell condition being the principal variables of greatest contribution to inaccuracy.
You say the percentage estimation of remaining capacity would be worthless if amps (current draw) “were a major determination”. I never suggested current draw was a major factor, it is one of many factors that are used by the SOC to estimate time to empty.
Temperature also is an important consideration and is also a factor used in the estimation of capacity and remaining time. I’m not sure what point you might be making with respect to your comment that temps should lower volts more quickly? LiION, like other chemistries, offers improved performance as temperature increases (the trade off being reduced life).
The various battery monitoring SOC’s employed in DJI batteries (sourced from Texas Instruments) are well known. If you are interested in understanding how they operate have a look at the white papers. The principal algorithms employed and their operation (including what parameters are measured and their importance) are referred to “Gas Gauge” and “Impedence Track”.
TCOPE I am not guessing any more than you are. Unfortunately you seem to be relying to a large extent on a combination of outdated technology and a flawed understanding of several key concepts.
Are you seriously suggesting that DJI might go to the trouble and expense of incorporating advanced battery management SOC’s in their products only to then not benefit from their features? That they might simply take the voltage and % remaining data from the SOC? That is a ridiculous assumption. I don’t think they could possibly be that silly. Luckily it is apparent that they aren’t. The fact that the remaining flight time depicted in GO is demonstrated to be as accurate as it is and so effective in accounting for actual flight conditions and battery health demonstrates simple voltage measurement alone is not the scheme employed.
There is no question that the difference between individual cell voltages (call balance) can be very important. I agree we should be paying attention to it. The fact remains however that monitoring overall battery voltage in flight is significantly less reliable and accurate in determining remaining capacity than observing the reported battery % and estimated remaining flight time.
Distance from home point (or specifically the estimated time to return to home) obviously is and must be a factor. The other important factor is the estimated remaining flight time determined by the battery management SOC (time until empty), voltage being only one of many factors that contribute to its estimation.
Of course voltage tables relate to voltage. Cell voltage has been used to estimate the state of charge of battery cells for a long time, well before LiION cells were available. The concept is a simple one, voltage indicates state of charge which, for a known cell capacity and cell chemistry, will allow remaining charge to be estimated. Its application is simple to implement, a “voltage table” is created by terminating the cell with a precision dummy load and measuring and plotting cell voltages during cell discharge against cell capacity minus Ah delivered. The limitations of this scheme are well known. Cell temperature, current demanded by the load and cell condition being the principal variables of greatest contribution to inaccuracy.
You say the percentage estimation of remaining capacity would be worthless if amps (current draw) “were a major determination”. I never suggested current draw was a major factor, it is one of many factors that are used by the SOC to estimate time to empty.
Temperature also is an important consideration and is also a factor used in the estimation of capacity and remaining time. I’m not sure what point you might be making with respect to your comment that temps should lower volts more quickly? LiION, like other chemistries, offers improved performance as temperature increases (the trade off being reduced life).
The various battery monitoring SOC’s employed in DJI batteries (sourced from Texas Instruments) are well known. If you are interested in understanding how they operate have a look at the white papers. The principal algorithms employed and their operation (including what parameters are measured and their importance) are referred to “Gas Gauge” and “Impedence Track”.
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Distance from home point shouldn't be a factor of % charge, unless it is a fudge factor to mentally influence you to return home sooner, rather than get yourself in trouble. Otherwise, whether you are 100ft or 3 miles, the charge status is the same. Now the RTH point does change but that's a different issue.
Indeed. The same applies to sitting powered on with the props off. The issue I was addressing with TCOPE was to what extent battery voltage might be relied on in determining the battery state of charge. Remaining time and depicted charge % are significantly more accurate and informative than voltage.
ac0j
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The Mavic KNOWS when you need to RTH. It will give a pop up advising you to come home.
If you ignore that warning a couple times, it probably wont make it back. It doesnt have as much to do with voltage more than how much you used to get where you are, vs how much you need to get back where you started.
I agree 100%. I really started to mix information up on RTH and percentage of better left. I've since slept and it cleared up my thinking. Thank you for pointing that out.
While I like the "Smart RTH" and "Failsafe RTH" features that the Mavic offers, I would never rely on the "Low Battery RTH" feature to get me home. "Low battery RTH" does not account for atmospheric conditions such as head wind, flight path obstacles, or ground obstacles. "Critical Low Battery RTH" is the worst case, where the drone is landing no matter what, and if you cant see it, I hope it's in a safe area. Common sense is usually better than any algorithm.
How to use DJI’s Return to Home (RTH) Safely - DJI Guides
How to use DJI’s Return to Home (RTH) Safely - DJI Guides
BJR981S
Well-Known Member
It is recommended to fully discharge DJI batteries till they no longer turn on every 3 months to maintain battery health. This is not so much a a battery health issue (as discharging too low actually damages the battery) it is to allow the calibration of the smart battery. If you don't do this your battery "fuel gauge" will be inaccurate as the battery ages. You may not find this in a Mavic or any of the drone Manuals. It is in all of DJI battery Safety Manuals.
Failure to perform this calibration will cause sudden fuel gauge drops to low battery warnings on older batteries. This accounts for lots of fall from the sky's with sudden battery to zero issues.
Cheers Brian
Jamesb72
New Member
Personally unless flying, I wouldn't use the Mavic to discharge batteries - you're putting wear on the most expensive item. You can get a really nice lipo discharger and cable for around 1/3 the cost of one battery, so you can fully charge/discharge the batteries easily if you can't fly for any reason after charging, or over winter etc.
I use an ISDT discharger which is fully automatic, and a Mavic battery cable from ebay, which is a really easy and neat way to discharge batteries accurately to storage in around 20mins per battery.
I use an ISDT discharger which is fully automatic, and a Mavic battery cable from ebay, which is a really easy and neat way to discharge batteries accurately to storage in around 20mins per battery.
offshorecl1
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Watash48
Well-Known Member
Hmm that's interesting.
I'm new to drone flying but a very old hat at software and hardware.
My question has always been why do they call these batteries 'intelligent'?
Presumably because they have a microprocessor (computer) inside ensuring that all the necessary battery safety features are not violated, one of which should be ensuring against being discharged by the drone when the voltage falls below a certain threshold. This would be dead easy to implement in software if the micro is in charge of a relay or electronic switch which is only open when the battery voltage is above a certain threshold.
Is this happening?
Don't think about the drone suddenly falling out of the sky scenario because by the time this voltage point is reached the drone would have long been forced to land by existing battery safety features.
I'm new to drone flying but a very old hat at software and hardware.
My question has always been why do they call these batteries 'intelligent'?
Presumably because they have a microprocessor (computer) inside ensuring that all the necessary battery safety features are not violated, one of which should be ensuring against being discharged by the drone when the voltage falls below a certain threshold. This would be dead easy to implement in software if the micro is in charge of a relay or electronic switch which is only open when the battery voltage is above a certain threshold.
Is this happening?
Don't think about the drone suddenly falling out of the sky scenario because by the time this voltage point is reached the drone would have long been forced to land by existing battery safety features.
Check out this video, specifically at the 17th and 26th minute.
This guy is no dummy. Letting the battery go dead every six months or so is actually good for it. Doing so will also fix various battery error conditions. As he mentions, the software won’t allow a complete discharge which would kill the battery for good.
This guy is no dummy. Letting the battery go dead every six months or so is actually good for it. Doing so will also fix various battery error conditions. As he mentions, the software won’t allow a complete discharge which would kill the battery for good.
Do you have evidence of the so called fall from sky incidents?
There have been numerous accounts detailed on various forums where forced landings at critical level and total battery shutoff have been reported. Later analysis revealed in these cases the battery was one that had been partially charged at the start of the flight (usually by having entered auto discharge) or was faulty (usually bad cell).
The microconriollers and associated electronics in our packs don't need a deep discharge to calibrate- basic coulomb counting is yesterdays method of SOC monitoring. Cell condition including age and use related degradation is measured in our batteries and used by the fuel gauging algorithm. No need to stress your batteries with an outdated procedure.
Or you could use the battery power adapter to charge all your USB chargeable devices....
DJI documentation is sprinkled with misinformation and this is a classic example.
According to their Mavic 2 Intelligent Flight Battery Safety Guidelines ...
Travel Notice
1. Before carrying the batteries on an airline flight, they must first be discharged to a battery level lower than 30%
Extensive searching doesn't show any airline in the world asking for this.
The only place I find any mention of it is here in the IATA's guidance document for shipping lithium batteries as air cargo:
https://www.iata.org/whatwedo/cargo/dgr/Documents/lithium-battery-guidance-document-2017-en.pdf
The International Air Transport Association (IATA) is the international body that supports aviation with global standards for airline safety, security, efficiency and sustainability.
All airline lithium battery policies are based on the IATA standards.
And the IATA's guidelines for Passeneger Travelling With Lithium Batteries:
https://www.iata.org/whatwedo/cargo/dgr/Documents/passenger-lithium-battery.pdf
.... makes absolutely no mention of discharging batteries before travelling by plane.
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