Trouble With 5V Linear BECs in Parallel

Hello everyone,

I'm a pretty experienced builder and I'm working on my flight practice. I've built several multirotors without serious issue, but my second-hand Tarot 680 Hex is giving me a problem with the BECs.

Build: Pixhawk, Tarot680 Hex, 6x iPeaka SK40A (40A ESC, 3-6S w/ 3A linear BEC), Multistar 4S 5200mAh

My problem is that the linear BECs from my iPeaka SK40A ESCs do not seem to be sharing the current draw of the system (only charging 1 GoPro Hero 4). ESCs for motor number 1 and 2 become extremely hot when the GoPro is conected to draw power (measured 200F with my IR thermometer at 0.5 emissivity) while the other 4 ESCs did not become noticeably warmer. The GoPro is connected correctly, as evidenced by it's continued function and charging indicator activation when plugged into the 5V rail on the Pixhawk. Each BEC is rated for 3A and indeed, under the shrink there are 3 1A regulators on each ESC. My gopro was fully charged by PC before I connected it to my pixhawk.

Does anyone have experience powering peripherals on 5V using the ESC BECs? Is there a simple way to balance the load between all six ESCs? Or should this happen automatically?

It's almost as if current is being drawn from each ESC sequentially from #1 to #6. #1 became the hottest, followed by #2, while the others did not become hot.

Any help is greatly appreciated.

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  • Not all Linear regulators are created equal.....

    The one with the lowest internal resistance, will attempt to supply all the current.

    If you can tolerate a slight voltage drop, either solder some Schottky diodes, all with the stripey end pointing at your camera, in the + leads from your ESC's, or just some 0R25, 500 mW resistors.

    That should even out the current from each ESC.

  • It's considered poor practice to power a system with BECs in parallel. Sometimes it can work, but often times problems occur, yours being not the worst of the possibilities. You can blow up a BEC doing this.

    BECs are not like running batteries in parallel. A BEC regulates its output by sensing the voltage at what it's feeding and then adjusts output accordingly. But every BEC is just a little different and will respond to voltage changes in a way specific to that BEC. You are seeing exactly that with your most "sensitive" BEC providing most of the current. Multiple BECs can also fight each other, resulting in heating. I suppose if you had well spec'ed, carefully matched BECs you could pull something like this off, but BECs in ESCs are anything but that.

    If you are running only a GoPro then one 3 Amp BEC should be plenty. Just disconnect the +5 volt center wire from the servo connectors of the remaining 5 of your ESCs and you should be fine with just the GoPro.

    • What this guy said.

      In addition, if you are desperate to use multiple BEC in parallel, then run each through its own Schottky diode.  The outputs of the diodes can then be used in paralleled.  This will prevent the linear regulators from fighting each other.  

    • One of the weirdest problems that I discovered was that when I only connected the 5V pin of ESC #1 to the pixhawk and powered the gopro from there, the ESC temp measured 300F max at 0.5 emissivity. ESC #2 also became very hot when powering the gopro solo. I'll try the others to identify if ESCs #1 and #2 are experiencing BEC issues.

      The ESCs run cool without their 5V pins connected.


  • Not sure if this helps, but I have a similar setup.  I have an independent BEC soldered into the PDB.  Draws directly from the battery rather than from the ESCs.  It's pretty cheap and easy to setup.  Or just get a smaller, independent battery to run your FPV equipment.  

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