Connect USB and power module at the same time?

Can I connect my APM 2.5 to the computer using the USB-cable and at the same time connect my 3S battery to the 3DR Power Module (connected to the APM) without damaging anything?

I read somewhere (without much motivation) that it could damage the board. Suspect that it will be ok if the current from the power module isn't to high? I saw a table somewhere on the but can't find it now of course.

The reason for asking is that I want to run "compassmot". The instructions doesn't include any warning about this however.

If it can be a problem, is this valid alternatives?

1. Run compassmot using the wireless telemetry module?

2. Create a custom USB-cable without the power pins attached?


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  • The APM 2.6  I bought (3DR) died when I had an SBEC providing 5.2V to the RX and with the RX connected to the APM.

    As soon as I plugged the USB in it fried the two components next to the USB and seems to have taken out the 3.3V.


    As for the PM???  I have not risked it until I have the 2.6 Eagle files.



    • Can you give more details about which chips fried. A pic with the chips circled would be nice.
      • Ok,

        This is the failure mode I have researched.

        1.  I connected an SBEC to my rx and powered the APM from the rx leads.

        2.  I connected the USB lead to my Laptop.

        3.  It initially connected ok

        4.  I had a wiff of burning and the Usb connector was hot.

        5.  Looking at the board the two components next to theUSB were fried.

        6.  The usb connector was also distorted.

        7. The 3.3v regulator on the board had also stopped working.

        How did this occur:

        1. There are noprotection diodes between Vcc and USB+5v

        2.  When you power the apm from Vcc+5 and then plug in USB current only limited by the laptop +5v USB chip flows if thedifference in voltage between Vcc and Usb+5 is sufficient.

        3.  The wires inside the USB connector insulationmelts and shorts the D+ to the USB +5.

        4.  This blows L1 in the APM and the zener diode.

        So how do you prevent this.

        Make a USB cable without the red USB+5V connected.

        Only power the A PM and rx from one source of 5V.

        You can then plug the USB in with the APM powered as the finished quad..

        Hope this helps..


        • John thanks for sharing an excellent report. I think this summarizes pretty well what's happening and mainly gives us a solution with "unpowered" USB cable. 

    • Sad to hear John. Maybe it is because you are powering your RX via SBEC (ESC) ?

      I am powering my RX from APM 2.6 which in turn is powered by 3DR power module.

      But I still don't dare connecting both USB and battery.

      • i think you can otherwhise how you can program the power module in mission planer O.o

        • Read my analysis below.
  • So to summit it up. What the final answer?

    Is it possible to connect APM (with 3DR/APM power module) via USB cable to PC with Mission Planner and at the same time connect a battery to APM, without damaging the board?

    • It's definitely possible, you can connect the APM to the computer and at the same time connect a battery without any problem.

      I have done it several times , and as Tom points out - it's documented in the official wiki as well:


  • Hi,

    I am using an APM 2.6 and I want to control a robotic hand with it. This thing is a totaly "ground - project", so it will not move at all. However, I do have the following problem:

    Do I damage the APM, if I connect the power module and the USB at the same time? I want to get all the data from the APM in a small computer and as long as I have a fixed place for my robo hand i want to use calbes. I also want to control it with a joystick.The problem is, that my computer cannot power the APM. Its USB power output is too weak. So does it work to connect both without damaging the APM?


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