DJI F550 battery question

[UgashikBob]

During one of the first attempts to hover my F550 I would get the first and second level battery alarm and unit would descend. After shutting off the battery alarm in assistant it worked ok for a few very short flights and now it will start descending because the telemetry data shows the battery droping to 6.6-6.7 volts and then going to 11.3 after landing. When I recharge the charger starts at 11.9 and goes to 12.60 and only shows 820mah of the 5000 used. The battery is a Sky Lipo 5000mah 30c. It was new with the unit and has had most of it use doing calibrations and maybe 45 minutes total flight time. Anything else I should look at before replacing the battery?

 

[Benjamin Kenobi]

Certainly sounds like a lipo problem. Unless something is causing a large current draw maybe? Were all the cells balanced after the flight?

 

[UgashikBob]

BK:
I balanced the cells on the last charge and they looked ok. Like you say it sure acts like a a large current draw. I see a drift to the right when hovering but don't think that is related. See nothing else unusual prior to rapid drop in voltage on telemetry data and then a smooth descent after approximately 1 minute of run time including the wait to acquire sats. Have two new 3S 5300mah 35c Glacier lipos on the way.
Thank you for your input.

 

[Benjamin Kenobi]

Hmm. It could just be a bad motor. Were you able to check the motor temps afterwards? You mention drift, is this with GPS mode? It should hold stable within a meter. Mine holds perfectly with no drift so check your calibration.

Let us know how the new lipo fairs. And maybe check your soldering for a dry joint.

 

[UgashikBob]

BK:
I had bad bearings in one of the six original motors and another that would surge/lock up. so I may try another flight while waiting on the battery to see if I have an overheating motor. Are the solder joints you refer to on the esc's and is there anything visual you can look for? The drift I mentioned was in atti and never tried GPS. I realize it should be stable but I suspect multiple problems and am trying to sort them out one at a time.

 

[Benjamin Kenobi]

Drift in ATTI is normal. A dry solder joint has a matt finish rather than shiny. Check where the ESC goes into the main board. I still think the lipo is the culprit. If the voltage dropped to 6.6V on the telemetry on a 3S lipo then that is bad. The absolute minimum should be 9.6V (3.2V per cell).

Cool?

 

[Benjamin Kenobi]

Unless the telemetry data is wrong of course? If the lipos were okay after the flight maybe it's you telemetry setup. Set to 3S?

 

[UgashikBob]

BK:
I am not aware of any setup for battery voltage in my Spectrum TM1000 telemetry module. Just wire the sensor inline with the battery connection and you get the readout with the DX8 telemetry display. I just did another tethered flight test and it didn't drop the voltage as rapidly but did drop to 7.2 in less than a minute. I measured the temp on all six motors and it was 73-75 degrees F so I'm sure its the battery.

 

[bruce365]

Hi UgashikBob, does your battery charger allow you to check your batteries internal resistance, that would indicate if there is a problem with the battery.
Regards - bruce

 

[UgashikBob]

Bruce:
I have a Sky Charger B6AC and I can't find anything in the manual regarding internal resistance. I had to change to EC5 connectors for theGlacier batteries. Just finished a six minute test flight with no problems so it was definitely a battery problem. After months of many problems it felt good to actually fly. Kept it in GPS mode and it would hover in place. Could the fact I have not adjusted the gains be a cause of the drift to the right in attitude mode?