25% Warning to Critical Battery Autoland in 10 seconds

[Parkerjh]

TWICE in the last week I have been using DroneDeploy on a mapping mission with Mavic 2.
In both cases, I got to 30% battery and Low Battery Warning and tried to start coming home when moments later, I would get a "Critical Battery" warning and start to auto-land. Flipping out of P mode and using sticks made no difference. This was two different batteries. I quarantined the first one until I had a chance to figure out if software issue or battery issue.

I can't for the life of me figure out how I can go from 30% to 1% in less than 30 seconds. In both cases, drone landed in a tree and I was able to fetch without too much difficulty but I definitely want to figure out why this is happening.



Thanks

 

[Meta4]

I can't for the life of me figure out how I can go from 30% to 1% in less than 30 seconds. In both cases, drone landed in a tree and I was able to fetch without too much difficulty but I definitely want to figure out why this is happening.

Look at your flight data and check battery.

DJI Flight Log Viewer | Phantom Help

Upload and view flight logs from your DJI drones

www.phantomhelp.com

You'll see that it registered as only 83% at the start.
If the battery was freshly charged, that should be a warning.

Then check the individual cell voltages, particularly Cell 4 after 4:40 and see what it's doing.
Cell 4 reaches critical low voltage (3.2V) at 9:17.7 and dies soon after.

 

[Parkerjh]

Look at your flight data and check battery.

DJI Flight Log Viewer | Phantom Help

Upload and view flight logs from your DJI drones

www.phantomhelp.com

You'll see that it registered as only 83% at the start.
If the battery was freshly charged, that should be a warning.

Then check the individual cell voltages, particularly Cell 4 after 4:40 and see what it's doing.
Cell 4 reaches critical low voltage (3.2V) at 9:17.7 and dies soon after.

thanks, I guess I still don't understand what forced a landing when battery showed 30%.

 

[Meta4]

thanks, I guess I still don't understand what forced a landing when battery showed 30%.

The 30% indication was misleading.
You had a dead cell ... the battery was cactus.

 

[sar104]

The 30% indication was misleading.
You had a dead cell ... the battery was cactus.

I haven't heard cactus used that way since I left the UK. Thanks for reminding me.

 

[slup]

thanks, I guess I still don't understand what forced a landing when battery showed 30%.

The battery percentage shown in the app is a calculation made by the Battery Management System (BMS) ... it's not always reflecting the actual status of your battery, what matters is each individual cell & their voltage in the battery.

Looking at your flight & both the cell voltages + voltage percent shows this depicted in a chart. See the legend below the chart area for what the graphs represent ... values shown there is from the point when the auto landing starts (pink area in the right side of the chart).

When you started this flight the BMS calculated the percentage to 83% ... but already there all cells weren't in the same voltage level as the others. Cell 4 deviated with approx 0,1V from the other 3 ... this deviation is considered to be "large" & this immediately when the log starts to be recorded (the motors starts).

But the BMS percentage calculation remains unchanged & the percentage is slowly decreasing on the base of consumed mAh during the flight. But the situation for cell 4 just gets worse, it heavily lags behind the other 3 with approx 0,25V.

But at 508sec into the flight the voltage for cell 4 rapidly falls & the deviation between the 4 cells hugely increases. At 621sec with cell 4 on only 2,62V the BMS realizes that something is seriously wrong & zeros out the percentage ... & by that the flight controller command landing ... cell 4 eventually ends up with a minimum of 2,18V & comes to rest after the landing on 2,8V.

So as said earlier... this battery was & definitely is cactus now.

(Click on the chart to make it larger)

 

[spudster]

Just sad that there is no battery charger / balancer / cycler available. These have been common in the RC industry for decades and the majority of enthusiasts own at least one. They will charge / discharge a battery and record the voltage, time, cell voltage, etc. throughout the complete charge/discharge cycle. Then display those results so you can decide if a battery is going bad. With many you an even hook to a computer so you can store the history and graph out the data. They can be pretty inexpensive, like this $65 unit that can hook to software to display/record the data.

 

[Kilrah]

This is all built in in DJI's batteries, if you look at logs with e.g. airdata you'll be able to see evolution as well.

 

[spudster]

This is all built in in DJI's batteries, if you look at logs with e.g. airdata you'll be able to see evolution as well.

Using flight data is not controlled testing, each flight is different so you really have no basis to go on. These cyclers do the testing under controlled conditions so you can compare each battery against each other and establish a baseline so you can if the performance has deteriorated. You could also test new batteries to make sure there are no problems with them before you fly with it. Being able to test may have revealed that the OP's pack had a bad cell and prevented him for losing the drone.

 

[Kilrah]

Airdata would have pointed out the bad cell as well as each cell's voltage is logged and airdata points out abnormal deviations. And each single flight is logged so if you look at the data you have more chance to catch a developing issue than in a once-in-a-while check.