Mavic Air 2 - Melted Battery

[Plafcan25]

Incase anyone is interested in cross-checking their batteries s/n associated with my melted one, here it is.

 

[SkyeHigh]

Incase anyone is interested in cross-checking their batteries s/n associated with my melted one, here it is.

The usual cause for a meltdown like this is an internal short within the individual battery cell.

The batteries are assembled in very thin layers with an even thinner insulating barrier between them. The insulator can breakdown allowing a short to occur rapidly heating the electrolyte, which causes further damage to insulating barriers, more heat and eventually leading to a thermal runaway or ‘event’ as the industry likes to call them.

Normally, and likely in this case, it’s a manufacturing defect and the reason DJI want to check the Serial Number in the event it is a bad batch or one-off. It can also be caused by overcharging and battery damage.

 

[nelsbb]

Thats probably a good thing, I guess the question I see is, if they detect a trend, how many batteries does it affect, how many in a production batch, assuming of course, that its not some odd design issue, considering how long they've been creating batteries for their products. And can they easily contact customers that may have potentially problematic batteries, not all in a batch could be flawed..

Just got the tracking number for the replacement. DJI has now asked for the rtn of the charger and charging hub and indicate there is a suspected issue with the charging system. Thry also asked for my "good" batteries' serial numbers which I suspect will be on a watchlist for future warranty if they were charged onvthe defective charging hub.

Overall despite a few hiccups in language/wording, I give DJI credit for their response. It will be 33 days from the case opening to receiving the replacement. 19 days of that will be in the hands of the courier. 1 day for assessment, 4 days for repsir/replace and 2 days processing and the test are weekend days.

Only down sides:

1) you get a survey after every email. Including your email submitting the survey!
2) they changed their mind on what needed to be returned 1/2 way through. I think this added a few days but it did not stop the process
3) they have yet to send the prepaid ups authorization for the extra bits they want back.

 

[nelsbb]

Thats probably a good thing, I guess the question I see is, if they detect a trend, how many batteries does it affect, how many in a production batch, assuming of course, that its not some odd design issue, considering how long they've been creating batteries for their products. And can they easily contact customers that may have potentially problematic batteries, not all in a batch could be flawed..

Ingobrecrived today indicates it was a charging hub issue that somehow affected the battery. No more detsilsbptovided thanbthat.

 

[kidroc]

My First Ma2 had a bad gimbal I have say I had a decent experience with DJI it was during lockdown too.

 

[Qazxswer]

Here's another one to add to the list. The flight went fine and I had no warnings until I landed it and it was extremely hot. Wouldn't turn off but I was able to get the battery out. This battery had only been used a handful of times. Drone is 2 weeks old. Hope DJI plays nice.

 

[LoganAir]

If any of you folks with blown batteries have an Airdata UAV account, it would be interesting to see the battery cell deviation report for the subject flight. Here is what the report looks like and captures one of my newer MA2 batteries with 3 total charges. You'll note that this particular battery is already showing deviations in cell number 3, which according to the legend below the chart, warrants watching. Would be interesting to see your data and what cell had the problem and maybe if there were warning signs in the overall trend. My other 3 MA2 batteries are very similar regarding cell #3 deviation rates in excess of 50 per minute.

 

[nelsbb]

If any of you folks with blown batteries have an Airdata UAV account, it would be interesting to see the battery cell deviation report for the subject flight. Here is what the report looks like and captures one of my newer MA2 batteries with 3 total charges. You'll note that this particular battery is already showing deviations in cell number 3, which according to the legend below the chart, warrants watching. Would be interesting to see your data and what cell had the problem and maybe if there were warning signs in the overall trend. My other 3 MA2 batteries are very similar regarding cell #3 deviation rates in excess of 50 per minute.

View attachment 109261

In my case. Deviations were zero. Voltage and amp traces were unremarkable. System showed 40% battery left on landing.

I had expected to see a cell go bad....but it was, as I said, unremarkable. If I showed you the plots of my good battery and the bad flight.... the only fifferencecwas the battery temp profile.

 

[LoganAir]

In my case. Deviations were zero. Voltage and amp traces were unremarkable. System showed 40% battery left on landing.

I had expected to see a cell go bad....but it was, as I said, unremarkable. If I showed you the plots of my good battery and the bad flight.... the only fifferencecwas the battery temp profile.

Understood, so in your case there were no warning signs in the data that would have raised concern prior to flight. Unfortunately with all 4 of my MA2 batteries I'm showing higher deviations that don't exist in the batteries for any of my other drones. This raises my eyebrows somewhat, given the damage others are seeing. Hopefully more folks will be able to report their trends. I may ground my MA2 until this is sorted out by DJI.

 

[everBit]

The usual cause for a meltdown like this is an internal short within the individual battery cell.

Absolutely wrong.
If battery has cells issue like short circuit it would cause drone crash as it could not supply enough power for the motors. Followed by turning off the battery itself by protection mechanism.
Noone with melted batteries has reported the crash.
But everyone has reported that batteries could not be switched Off.
Also in case of cell short circuit it should be the cells compartment to be melted but it's not the case.
Instead there is BMS compartment which is damaged.

So lets look inside Mavic Air 2 battery to determine the root cause while DJI silently replacing affected ones.



The melted hole located exactly against Charge and Discharge transistors which are NTMFS4C02N 230A rated n-Channel MOSFETs in SO-8 enclosure produced by ON Semiconductors.



If any of them is damaged then it starts overheating due to increased internal resistance while flowing significant current through them.
At this scenario damaged MOSFET could not be controlled by bms uC so battery output is always under power and drone could not be switched off (exactly like reported).

The same issue was once observed on M2P battery in my practice. The customer noticed the drone is powered on as soon as battery is inserted in the comapartment without double-pressing the button and battery begun to heat. He promptly reported to our service so it still was not melted. Diagnostics revealed damaged both MOSFETs. After their replacement the battery starts work just fine.

 

[LoganAir]

Absolutely wrong.
If battery has cells issue like short circuit it would cause drone crash as it could not supply enough power for the motors. Followed by turning off the battery itself by protection mechanism.
Noone with melted batteries has reported the crash.
But everyone has reported that batteries could not be switched Off.
Also in case of cell short circuit it should be the cells compartment to be melted but it's not the case.
Instead there is BMS compartment which is damaged.

So lets look inside Mavic Air 2 battery to determine the root cause while DJI silently replacing affected ones.

View attachment 109259

The melted hole located exactly against Charge and Discharge transistors which are NTMFS4C02N 230A rated n-Channel MOSFETs in SO-8 enclosure produced by ON Semiconductors.

View attachment 109262

If any of them is damaged then it starts overheating due to increased internal resistance while flowing significant current through them.
At this scenario damaged MOSFET could not be controlled by bms uC so battery output is always under power and drone could not be switched off (exactly like reported).

The same issue was once observed on M2P battery in my practice. The customer noticed the drone is powered on as soon as battery is inserted in the comapartment without double-pressing the button and battery begun to heat. He promptly reported to our service so it still was not melted. Diagnostics revealed damaged both MOSFETs. After their replacement the battery starts work just fine.

So what is the root cause of the MOSFET damage? Is it incorrect installation on the board or defects in design or manufacturing the chip itself?

 

[nelsbb]

Understood, so in your case there were no warning signs in the data that would have raised concern prior to flight. Unfortunately with all 4 of my MA2 batteries I'm showing higher deviations that don't exist in the batteries for any of my other drones. This raises my eyebrows somewhat, given the damage others are seeing. Hopefully more folks will be able to report their trends. I may ground my MA2 until this is sorted out by DJI.

I justed checked my good batteries' history files. 1 battery is showing a 0.2 v deviation on the number 3 cell. And a check of all files for all batteries shows if I have deviations, they are on cell 3. All fall into minor rating. I have no recorded major deviations of volts or maps.

 

[LoganAir]

I justed checked my good batteries' history files. 1 battery is showing a 0.2 v deviation on the number 3 cell. And a check of all files for all batteries shows if I have deviations, they are on cell 3. All fall into minor rating. I have no recorded major deviations of volts or maps.

Strange that so far it is only on cell #3. I have Mavic 2 Zoom batteries with 20 charges with no unusual deviations. Along with what 'everBit' posted about the potential MOSFET damage, it has me somewhat concerned...for all of us.

 

[everBit]

So what is the root cause of the MOSFET damage? Is it incorrect installation on the board or defects in design or manufacturing the chip itself?

My guess is manufacturing defect of MOSFETs used, probably the defected batch.

For many battery families DJI has used 1C530L 100A rated MOSFET which were paralleled in P3 and P4 ones to increase current throughput. This part has proved its reliability by time.

But now we see different type MOSFETs. Yes, they 230A rated against 100A but probably manufacturing technology still not perfect.

 

[LoganAir]

My guess is manufacturing defect of MOSFETs used, probably the defected batch.

For many battery families DJI has used 1C530L 100A rated MOSFET which were paralleled in P3 and P4 ones to increase current throughput. This part has proved its reliability by time.

But now we see different type MOSFETs. Yes, they 230A rated against 100A but probably manufacturing technology still not perfect.

Thanks for the explanation. Would there be any warning signs prior to failure other than what you explained regarding a battery that was already initialized during installation?

 

[LoganAir]

@everBit , interestingly, I ran across this thread the other day and didn't think much of it at the time.

Air 2 starts up when you put in battery

This has happened a few times now. Shut everything down ready to put away and I put in new battery to be ready for next time and it starts up. When you press the button two times it does not shut off and the back lights start blinking yellow really fast. Any thoughts?

mavicpilots.com

 

[everBit]

Would there be any warning signs prior to failure other than what you explained regarding a battery that was already initialized during installation?

Looks like it's the only sign, also If it occured midflight then battery temperature readings in the cells menu should be unexpectedly high enough but unfortunately pilots commonly not entering that menu during the flights.

I ran across this thread the other day and didn't think much of it at the time

Yes, it's exactly MOSFETs failure sympthoms described in the thread. So the failure was happened after the flight otherwise batteries would be already damaged in those cases.
May be during charging... Who knows.

 

[everBit]

If I showed you the plots of my good battery and the bad flight.... the only fifferencecwas the battery temp profile.

How much is this difference?
Could you show both profiles.

 

[Macinfo]

I uploaded some data to a free Airdata account and one battery shows some oddities over my other 2, though Airdata does say its minor and when you look at the other graphs, and compare to other batteries, it doesn't look all that much different, though perhaps its hard to spot that information in the other charts?

Free accounts do not display the data as noted in post 47.. because that display requires a paid account. Looking at My Logs, one battery stayed in the green but was close to orange on this dial display, the other batteries I have are not displaying data anywhere near that.. yet... I'll monitor this one battery more closely and see if this persists, if it does, may pursue a replacement before something does happen, as it is in Cell 3.

Another note, in a DJI forum, I noted it a couple times, the suggestion to remove the battery after flight, leaving the drone empty, is that a good standard practice, or is it overkill?

I guess another question might be, should one avoid the DJI combo charger? It only charges them one at time, the only advantage appears to be that you don't have to be around to plug in the next one. Is there a third party Mavic Air 2 charger that might work better yet?

 

[everBit]

the suggestion to remove the battery after flight, leaving the drone empty, is that a good standard practice, or is it overkill?

For flying on hot days it should be good practice as it allows faster cool down of battery cells thus prolongs their resource.