Hi All

I need help. I had maiden flight my skywalker 1680 with APM 2.5. There was no FPV gear and powered by 3s 5000mah battery. I am using a separate 3 Amp uBEC (max 5 amp) to power the APM to the input rail. so JP1 jumper was off. The ubec was given input from balance charging connector of main battery. The output rail of APM was connected to ESC.

After flying for 7 minutes at a slow speed and in circles i landed to have a look. The uBEC black (ground) wire was almost melted and about to short circuit. I was lucky to have landed.

So what is wrong. ?? is my APM drawing more than 3 AMPs?? not possible with JP1 removed . Please see image. The black wire of uBEC was melted on both its input and output side of uBEC.  

Have i wired them wrong or uBEC thin wires are crap?? Myu BEC was warm to touch but not very hot itself.

One more thing... i am using a 900mhz xbee telemetery module onboard. from where it draws power?? is this a drain on ubec?? does it draw power from input??

Secondly the moment i rev up the motor (sunnysky 1450 kv on 3s) bad compass warning came on mission planner HUD. remained there through out flight. i flew in manual so no harm. Its a RFI issue but how to solve that? i had carried out complete compass calibration earlier.

Any help would be appreciated.

regards all




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  • yes, Ahmed Rehan  rightly pointed out that your ESC ground might not connected directly to battery. ESC getting ground connection with battery via balance charger >> ubec>> apm>> esc speed controller  ground wire >> esc. Yes, check your T-Connectors

    • Thanks faraz and Rehan

      If this is the case then a thin wire of balance charger would have not survived for 7 minutes as i had pulled 30 amp and on average 15 amps.

      Would try to figure out. 

      i appreciate your help.


    • The thin wire didn't survive. A wire doesn't just magically break at 5A, it overheats first which is exactly what you have seen. If you are asking for advice, don't argue with it!

      Circuits are a complete loop, if only the black wire has melted then current is coming from somewhere else and returning to the battery via that wire. You need to check your wiring.

    • Hi Ben

      Point taken!!

      Let me recheck everything again.


  • It seems you are getting power +ve from main wire of battery and ground from balance connector other wise both wires should melt check your main connection to speed controller it is not connecting main ground wire it is taking ground from your balance connector. This is mainly problem with T type connector.
    • AoA

      Dear Ahmed Rehan. thanks for quick reply.

      From which country you are? if you are from Pakistan , i can call you to undersatnd better.

      I have my speed controller on output side. ubec is on input side of APM powering APM and xbee module. the output is powered by ESC. these two sides are isolated as i have removed JP1. 

      Which T type connector are u refereeing. can u please elaborate.

      regards and thanks

      arif saleem

    • Check the output from the BEC, is it the correct voltage?

      I once connected one the wrong way around as the connectors had been cut off, everything worked, except after a while it destroyed the rudder and elevator 9g servos, as the servo rail was being powered with 12v not 5v as I wanted.

      Good luck,


    • Hi Keith


      But this is the input ubec powering the APM,(with JP1 removed)  its not at the output powering servos.

      Any thoughts??


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