Mavic went from 96% battery at takeoff to 0%

[boblui]

Boblui, for clarity and my own education what are BatteryInfo:Current & BatteryInfo:BatCurrent ? ooops the smilies are meant to be colon D

As you understands very well. Nobody knows for sure what these fields represent so it's just my guess. I think BatteryInfo:Current is the current delivered by the battery in mA. It's quite close to the sum of the motor currents ( in Amp ) :



No idea on what BatteryInfo:BatCurrent is. The number is negative.

 

[Deleted member 103366]

It's just I find the idea of 12A etc. coming out of a 'small' battery jaw dropping and you do seem very well informed as to what individual columns detail so, I wondered if you had found a source of information.
There was/is a post by BudWalker that contained a link that I have not yet followed but might lead to column information. I will have to try and find that post again.

 

[boblui]

It's just I find the idea of 12A etc. coming out of a 'small' battery jaw dropping and you do seem very well informed as to what individual columns detail so, I wondered if you had found a source of information.

I dont have any source of information but just use my judgement as an electrical engineer.

From the chart above it can be seen that when the craft was not climbing BatteryInfo:Current was just about 6.5A.

From the spec of Air 1 the hovering time is 20 min and the battery capacity is 2375 mAh. Assuming 75% efficiency the hovering current is worked out to be 5.3 A so it's not too far away from that shown in the chart. My understanding on the meanings of the data fields in the log file is mostly based on this kind of cross checking.

 

[Deleted member 114292]

It's just I find the idea of 12A etc. coming out of a 'small' battery jaw dropping and you do seem very well informed as to what individual columns detail so, I wondered if you had found a source of information.
There was/is a post by BudWalker that contained a link that I have not yet followed but might lead to column information. I will have to try and find that post again.

12A is quite expected. I have a drone with a current meter on it not much difference in size and it draws 12 A per motor ascending fast.

 

[Kilrah]

Can't see individual cell voltages but for the total voltage to fall down that much with a cellVol that'still above 2.6 basically all of this battery's cells are dead.

 

[Deleted member 103366]

Can't see individual cell voltages but

in CsvViews charts of the DJIFlightRecord_2020-12-22_[13-46-17].txt log look in the CNTR_BATT section, in a csv produced by CsvView they appear in columns DJ to DL (114 to 116)

 

[BudWalker]

As you understands very well. Nobody knows for sure what these fields represent so it's just my guess. I think BatteryInfo:Current is the current delivered by the battery in mA. It's quite close to the sum of the motor currents ( in Amp ) :

View attachment 119916

No idea on what BatteryInfo:BatCurrent is. The number is negative.

I suspect that BatteryInfo:Current is just a smoothed version of -BatteryInfo:BatCurrent. That's especially apparent at motorStart where BatCurrent coincides with the motorSpeeds but Current lags.


In the older platforms battery current was always negative and had to be negated by DatCon.

 

[Kilrah]

in CsvViews charts of the DJIFlightRecord_2020-12-22_[13-46-17].txt log look in the CNTR_BATT section

Had only seen the dat, not the TXT.

But anyway, just the same as this one:

Mavic Air | Critically Low Voltage Warning | Max Motor Speed Reached

Hello, Had a scary flight yesterday afternoon. My Mavic Air took off, hovered for around 1 minute, and then gave me an error about battery being too low and max motor speed reached. It took a little bit harder of a landing than I wanted it to however just looks to be cosmetic scratches on the...

mavicpilots.com

 

[offtheback]

My only experience like yours was with a battery in my M2P. It was caused by a failed cell.

Me too.Landed in marsh grass.By the time I found a boater to take me there it had had taken a bath.

 

[hiflyer201]

Too much information alert!
When a battery fails, Airdata will generally show that the battery in question has had several critical deviations in recent flights.
I've had three Air 1 batteries land with a critically low warning. The first was a surprise, but after that I began checking on Airdata. The second two had shown several critical deviations during recent flights but I continued using them as I was flying very low in active track over good terrain. Many times checking the cells in flight showed all in the green..but airdata showed a different story. The first failed battery I flew again several times low in my backyard..several times it failed but not every time. The flights were short duration.
I have six Spark batteries and only one has ever shown critical deviations. All of those have less than a hundred charges each.
One of my three Air 2 batteries has shown a critical deviation and that was with only a ten or so flights. Something to keep in mind.

 

[sbell1967]

Called DJI today to see what can be done without retrieving the drone (since I have all the flight data, plus the screen recording of my flight from my tablet).
They can only create a case and look at the data if it was under the 1st year of the manufacturers warranty. I'm on my 2nd year of Refresh and they won't even look at it. And of course my Refresh expires tomorrow...so basically I'm screwed.

 

[kydroneman]

And of course my DJI Refresh is no good without a body ?

won't help you now but i passed on refresh and took out a personal articles policy with state farm. I lost my drone in the river and called them up and told them. they mailed me a check within the week fore full price for what I paid.

 

[Meta4]

Then all of a sudden I get a critical battery warning and a RTH warning. Then the battery dropped to 0% and it autolanded.

Now you can see the cell voltages:

DJI Flight Log Viewer | Phantom Help

Upload and view flight logs from your DJI drones

www.phantomhelp.com

Critical low voltage for a single cell is 3.3V.
By 52 seconds, two cells have fallen below 3.3V under load, and continued to fall further.
As explained, the % indication is completely false.

 

[SpitFire]

Just want to ask a question. about the BMS, the small computer inside the battery. Is there anyway to detect a problem with the battery before failure.
I have had one battery for four years now, and have it marked to keep a eye on it. But no idea as to what to look for, as advance warnings about BMS failure. I try to prevent things from happening, like with my motors, checking temp of each motor. Recording temp of each motor, turning the prop by hand to feel or hear any strange noises ETC. Any body have any preventive info to share please?

 

[dave canada]

my pro did that last month took off got up to 130 ft and then did a belly flop I have three dji batteries that and three power extra and I hate to say it but the later have been more dependable and have yet to overheat or puff up or drop my drone out of the sky and there isn,t any difference in flight time per flight. A big difference in lasting time with out problem

 

[Meta4]

Just want to ask a question. about the BMS, the small computer inside the battery. Is there anyway to detect a problem with the battery before failure.

You can use Phantomhelp to check the way a battery is performing by checking the cell voltages and how they run down over a flight.

I try to prevent things from happening, like with my motors, checking temp of each motor. Recording temp of each motor, turning the prop by hand to feel or hear any strange noises ETC.

Brushless motors are exceptionally reliable and resistant to problems.
You are probably wasting your effort being anxious about them.

 

[JackL]

How much is known about the BMS? Does it just send data to the FC or can it regulate voltage and current coming out of the battery?

Just a few more words on why the battery % dropped from 86% to zero in no time. The battery capacity detected by the BMS ( Battery Management System, a small computer inside the battery ) at the beginning was 2136 mAh which is reasonably close to 2375 mAh stated in the spec so no problem there. As the battery is discharged, the BMS integrated the current with respect to time to come up with the no. of coulombs ( or mAh ) taken out of the battery and used that to calculate the battery % figure. At the same time, the BMS was monitoring the battery voltage for the purpose of updating the battery capacity - a process known as battery calibration.

If I have done this correctly it appears all the cells somehow failed at the same time and magically recovered. I have never observed that with a lipo battery pack. Could dirty battery terminals cause this?

 

[sbell1967]

How much is known about the BMS? Does it just send data to the FC or can it regulate voltage and current coming out of the battery?



If I have done this correctly it appears all the cells somehow failed at the same time and magically recovered. I have never observed that with a lipo battery pack. Could dirty battery terminals cause this?

View attachment 119986

Nope...batteries were checked out and drone contacts and batteries were good. And the batteries each have about 15 flights on them (if that).

 

[JackL]

Nope...batteries were checked out and drone contacts and batteries were good. And the batteries each have about 15 flights on them (if that).

It seems weird they were on a steady decline and suddenly came back to where you would expect after the glitch. I know literally nothing about analyzing logs or what goes on inside a DJI drone so it is all speculation on my part while I try to learn. I hope they give you a new drone since this definitely does not seem like pilot error, imho.

 

[Meta4]

It seems weird they were on a steady decline and suddenly came back to where you would expect after the glitch.

It's no mystery, that's what happens with batteries.
The voltage drops while the battery is under heavy load and bounces back when the flyer eases off on the sticks.

Having the battery fall below critical low voltage less than a minute after launching shows that the battery was in very poor condition at the start of the flight.