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Thread: IMPORTANT: BEC on ESC and Avoiding high current system ground loops

  1. #1

    IMPORTANT: BEC on ESC and Avoiding high current system ground loops

    If there ever was an FPV NOTAM, this is it.
    This has to be shared asap.
    I've seen one too many burnt current sensors and potentially damaged OSD.
    Click image for larger version. 

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    The reason?
    Ground loops sharing high ESC current.
    Where do those ground loops emanate from?
    BEC ON ESC!!! (they were NEVER intended to power complex systems - give them up)

    If you fly a foamy for fun off of a BEC on ESC with nothing else in the power line then fine.

    If however you have a current sensor and other FPV or UAV hardware then you CANNOT feed the ESC ground line back to your system.
    You will pass motor current through the ground tracks/wiring of your system.
    Minimal current (1~2A) over long cables will push the ground rail positive, reducing your 5v system power and trigger brown outs, system resets etc. You will loose control and be unable to RTH.
    Anything higher than 2~3A and tracks will burn.
    You've been warned.

    Below is how to get it right.
    FULL SIZE LINK TO DOWNLOAD
    Please ask questions if not clear on any points.

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    Ren

    not having much luck attaching full size images
    I'll host them for now but can admin do something for me?
    At 350kb a pop I'll be thrashing my server - cheers
    Last edited by sublime.f; 3rd April 2011 at 11:53 AM.
    "\(`f`)/" - I take things apart! - Waffles?! try "dora-yaki" its like two pancakes fighting over the toppings - safe among geeks

  2. #2
    Beginning Crashpilot Royalfm's Avatar
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    Hmm, i just realised that the integrated BEC of the ESC wont be enough in my glider. Well im on my way to fly FPV but so fare im learning to fly the normal way. I just want to ask about my wiring if im thinking right the way it looks and if i need the GND between the ESC and the UBEC or not cause at your picture its not connected.

    Empfänger = RX (called in German )
    Motor = Engine (for sure )

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  3. #3
    Royalfm,

    if you intend to fly FPV/UAV etc... just don't use the BEC on ESC until you understand the diagram I posted and the reasons why.

    People on RCG asked me if its ok to use it... well yes, as long as you know what you are doing.

    copied over from RCG
    As regards the TwinstarII
    I'm offering the suggestion that instead of not utilizing the BEC on ESC (I have two 18A ESC with 2A BEC) why not feed the AILERON servo directly at the wing.
    My initial purpose to this was to cut down on wiring and weight.
    Powering the whole system off of an ESC/BEC has always been against my reasoning.
    Last edited by sublime.f; 3rd April 2011 at 03:42 PM.
    "\(`f`)/" - I take things apart! - Waffles?! try "dora-yaki" its like two pancakes fighting over the toppings - safe among geeks

  4. #4
    Navigator PnoT's Avatar
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    He's actually updated his image over on the other forums so you might want to swap that one out for the latest.
    "1.3GHz 850mW video transmitter. Warm as hell. Drains power as thirsty camel." -Rastislavko

    "At this point DL was an option, sat back and saw more feedback from buyers. Start getting good range results 12-15-17km 20-22-25km? From a $320 system??? Looks good, really good. Price drop to $269, end of story..." -Po73

  5. #5
    Kiwi in Germany whakahere's Avatar
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    Just to be clear here ... that sensor picture is mine .. my hand and I was NOT using the bec on my esc. It burnt out I believe because I had the power coming from between the current sensor .. to my bec and the line flowed to the esc. To tell you the truth I have really little clue why it burnt out still if it states you shouldn't use the bec on the esc ... cause I didn't!
    Whaka's Tinkerings blog --> http://fpvlab.com/forums/showthread.php?36623-Whaka-s-Tinkering&p=631753#post631753
    Battle H Virus (home build basher quad tutorial) --> ]http://fpvlab.com/forums/showthread.php?12544-Tutorial-Battle-H-Virus
    Range record on 5.8ghz 200mw 24km --> http://www.rcgroups.com/forums/showthread.php?t=1441664

    The one thing I know how to do well with FPV - crash. All in a day of fun!
    I believe landing is a full body experience .... I do my best to aim for your body.

  6. #6
    Quote Originally Posted by whakahere View Post
    Just to be clear here ... that sensor picture is mine .. my hand and I was NOT using the bec on my esc. It burnt out I believe because I had the power coming from between the current sensor .. to my bec and the line flowed to the esc. To tell you the truth I have really little clue why it burnt out still if it states you shouldn't use the bec on the esc ... cause I didn't!
    I think you are on top of the root cause now.

    Basically a high current ground loop will damage things that aren't rated to take the current you push through them.

    The reason I point my big finger at ESC/BEC is that they are "plug & play" high current ground loops for OSD/UAV setups.
    Use a ESC/BEC without being aware of the required precautions and be doomed.
    "\(`f`)/" - I take things apart! - Waffles?! try "dora-yaki" its like two pancakes fighting over the toppings - safe among geeks

  7. #7
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    And what if you don't have the current sensor and the OSD. I do use a separate bec on a single battery system.

  8. #8
    Kiwi in Germany whakahere's Avatar
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    Quote Originally Posted by Garbach View Post
    And what if you don't have the current sensor and the OSD. I do use a separate bec on a single battery system.
    At this point you don't really need to as the camera and video tx often don't make ground loops. The best thing to do would be to post your wire diagram here and we will let you know. My way of checking for ground loops is now very easy (thanks to Sublime for explaining alot of this). Get you finger on the battery ground and move you finger over all of your grounds that you have. First rule is you must only go on a cable once. If your finger leads you back to a ground that you have been on before you have a loop. If it is between the battery and the esc/bev then you will need a separate bec.

    Well it makes sense in my mind
    Whaka's Tinkerings blog --> http://fpvlab.com/forums/showthread.php?36623-Whaka-s-Tinkering&p=631753#post631753
    Battle H Virus (home build basher quad tutorial) --> ]http://fpvlab.com/forums/showthread.php?12544-Tutorial-Battle-H-Virus
    Range record on 5.8ghz 200mw 24km --> http://www.rcgroups.com/forums/showthread.php?t=1441664

    The one thing I know how to do well with FPV - crash. All in a day of fun!
    I believe landing is a full body experience .... I do my best to aim for your body.

  9. #9
    Shedding light over FPV HugeOne's Avatar
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    Wink

    As regards the TwinstarII
    I'm offering the suggestion that instead of not utilizing the BEC on ESC (I have two 18A ESC with 2A BEC) why not feed the AILERON servo directly at the wing.
    My initial purpose to this was to cut down on wiring and weight.
    Powering the whole system off of an ESC/BEC has always been against my reasoning.
    I tried it, doesn't work. The ESC shoot to much ripples into the negative rail, the servos start the wiggle fast as you open the throttle. But then, maybe the fast wiggle of the ailerons could produce thrust...mmmm

  10. #10
    Pilot JBeauford's Avatar
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    Quote Originally Posted by whakahere View Post
    ... The best thing to do would be to post your wire diagram here and we will let you know. ...
    I'll take you up on that offer! After reading about the ground loop issue I revised my wiring diagram (attached) the minimum amount necessary to (hopefully) solve the problem. Basically, all I did is remove the ground wire from the RSSI and the ESC connections. So now RSSI and ESC connections have only the signal wire. I'd appreciate it if you would take a look and let me know if you think further revisions are necessary.

    Thanks,
    Jeff
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