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

jordannaval

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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 outsides, props surprisingly still in tack and not broken/bent. I thought it had to do with operator error by putting in a battery that wasn't charged so I tried again to let it hover with another battery with the same issue.

I gave it a break for awhile and tried it again one more time to let it hover hours later and again the same issue. It baffles me because it flew fine that same morning and I have many flight hours with this thing. I took a look at the logs which I have here for the first flight:


From my basic interpretation of this (and I could be wrong so please correct me if that's the case) that the battery report seems to coincide with it flying for a short time and then dropping rapidly. Is this a problem with a bad battery or the drone itself reading the battery levels incorrectly.

Thank you in advance for any feedback, this has been stressing me out all day trying to figure this out and searching online however not finding anything specific to the Mavic Air.
 
Hi Kilrah,

Thanks for input! Can that be determined if all three batteries did that? Had a successful flight that same morning which is why I'm curious.
 
Yep pretty much, if you see the voltages matching a full battery at the start and falling down off a cliff to below minimum discharge there isn't really anything else that it can be.

Someone posted the same issue yesterday also with an Air, so I guess the Air batteries tend not to age well...
 
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Hi Kilrah,

Thank you for quickly responding!

In regards to the log that I posted, would voltage you are referring to be in "Battery Voltage"? (I know it sounds like a dumb question but want to clarify because it looks like it starts at ~12v then drops to ~8v then goes back up to ~11.5v which makes me wonder if this is a reading issue with the drone itself and not actual battery degradation.
 
Both the total voltage and the 3 cell voltages. The individual cell voltages not being way off each other shows that it's not just one cell that's dead but all 3 are similar.

Voltage went up as current reduced becasue the climb was stopped, pretty normal for batteries that have their internal resistance that went up.

What's interesting is that afterwards with relatively constant current the voltage continued going up. Either temperature helps since that went up too, or those batteries develop some kind of insulating layer when sitting unused that degrades performance and it gets "burned through" when put under load for a while again. In the latter case maybe a couple of cycles could bring them back to usable state.

Were those batteries sitting around unused for a long time until yesterday?

1608734024317.png
 
Hi Kilrah,

Thanks for the detailed information, I appreciate it along with your patience.

To answer your question, the last flight I took was the morning of and prior was a week and a half ago.

All the Best,
Jordan
 
Updated log with a ~2min flight hovering and battery seems to look better after firmware refresh. Let me know what you think and will try a longer flight when sun comes up


Does this look better?
That is a different battery .....

The previous one :

1608736482918.png

This one :

1608736504347.png

I am interested in knowing the history of the apparently problemetic battery in the first post. When was it used last time ? was the flight normal ? any log ?
 
That's almost constant current but still a big dip with strong imbalance before climbing again once the battery warms up... only seen that on badly worn out packs.

If it was me I'd probably do a couple of full cycles (basically leave the aircraft hover 50cm from the ground for the whole pack) and look at the logs by curiosity but without expecting much.

Basically... battery's good for the trash along with any other that behaves the same.

Clipboard01.png
 
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Hi Kilrah,

Thank you again for the response. I'm not sure if I noted prior, but the error with the battery power was with all 3 batteries that I had (did 3 flights with them during the time of error). Posted only one log to save time, however I can post the rest of them.

Did another test with another of the supposed failed batteries and got this


Flight was successful with test hover for a little and then increasing altitude to 300ft in a 400ft zone and no increase of battery loss during flight. Only landed to not exert the craft too much in this test. Firmware refresh seemed to help and surprised very glad it did. Will continue to test the rest of the day and keep updated to hopefully help others with this issue.
 
When LiPo battery cells drop below 3,0V they will rapidly sustain damage as it's resistance increases fast & this change is permanent. This mean that it will be very prone to large voltage sags as soon as it's under load ... also it can heat up significantly during charging/discharging & it will most probably soon start to suffer from swelling.

The cells in that battery fell well below 3,0V ... cell1: 2,61V cell2: 2,69V cell3: 2,25V

1608748818047.png

I would treat this battery with caution, charge supervised & not fly with it anymore ... only good for desk duties like adjust settings, upgrading firmware & emptying the internal memory.

Both batteries that you have in the logs that you have attached are manufactured Oct. 23 2018 ... those batteries that you have, was they included in the Fly More Kit? Maybe all of your batteries have the same behavior & need to be replaced.
 
I managed to find another flight log of Mavic Air ( attached ) in the forum and did a comparison with that of yours :

1608793140669.png

Both logs start with 98% battery and have the battery % figure dropping gradually but your battery had the voltage dropped by a LOT more and unstable.

I think the BMS ( Battery Management System, a small computer inside the battery ) has done an exceptionally bad job in monitoring the capacity of the battery hence the highly misleading battery % figure. Not sure if firmware update will fix that indication error. The battery % should have dropped to zero shortly after take off but it kept telling a very high % figure. I can be quite sure that if you keep flying with that battery, at some point the battery % would drop to zero suddenly and took you by surprise.
 

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