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  1. #1
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    Question Dual BEC and evx-2? Powering 2 hungry servos

    First of all I would like to apologize if a similar thread already exists. I was trying to find one, but there either is none or my english isn't good enough to type in the right words...

    Anyway... after I burned out one of the stock steering servos on my summit I decided to replace both of them with two sav÷x sw-0231mg servos. Since these servos require a lot of current I decided to run them through separate BECs (1 BEC for 1 servo) and bypassing the rest of the electronics to prevent over "currenting" of the rx or ESC BEC. I've read somewhere that this is possible by connecting the external BEC directly to the servo, leaving the ESC one connected. Then I connected just the servo signal to the rx only to find out that I would also need to connect the negative to the rx...

    This where it gets hot... I wanted to power the BECs through the balancing connector of the main LiPos (1 BEC connected to the left LiPo and 1 to the right LiPo). Well I tried just that and as soon I connected the BEC the ground wires on the BEC and ESC went up in smoke. I did now find out that there is a BEC and non BEC side of the ESC... is this cause of the short? My friend will also run the same servos but with a single "giant" BEC and when he connected the way I did everything worked...

    Is there any way to make things work the way I imagined or should I just find somewhere a 10A BEC that isn't the size of a brick and doesn't cost a fortune?

    Any help/advice is going to be very appreciated. I'm now going to continue to estimate the damage on the evx-2...

  2. #2
    RC Turnbuckle Jr. jamann's Avatar
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    Quote Originally Posted by Madatij View Post
    First of all I would like to apologize if a similar thread already exists. I was trying to find one, but there either is none or my english isn't good enough to type in the right words...

    Anyway... after I burned out one of the stock steering servos on my summit I decided to replace both of them with two sav÷x sw-0231mg servos. Since these servos require a lot of current I decided to run them through separate BECs (1 BEC for 1 servo) and bypassing the rest of the electronics to prevent over "currenting" of the rx or ESC BEC. I've read somewhere that this is possible by connecting the external BEC directly to the servo, leaving the ESC one connected. Then I connected just the servo signal to the rx only to find out that I would also need to connect the negative to the rx...

    This where it gets hot... I wanted to power the BECs through the balancing connector of the main LiPos (1 BEC connected to the left LiPo and 1 to the right LiPo). Well I tried just that and as soon I connected the BEC the ground wires on the BEC and ESC went up in smoke. I did now find out that there is a BEC and non BEC side of the ESC... is this cause of the short? My friend will also run the same servos but with a single "giant" BEC and when he connected the way I did everything worked...

    Is there any way to make things work the way I imagined or should I just find somewhere a 10A BEC that isn't the size of a brick and doesn't cost a fortune?

    Any help/advice is going to be very appreciated. I'm now going to continue to estimate the damage on the evx-2...
    1 Castle 10amp bec should power those servos.The evx2 is wired differently to most others.You need to pull power from the stock bec side as it is wired in series internally after it pulls bec voltage.it will short if you try to use both batt to feed it
    If you want to power just the steering servos from the bec the only wire needed from rx is signalUsually white)some use the ground as well I did not, I just pulled signal.the stock bec will power everything else as normal.there is a thread on it here I believe.i will have a look for you if someone else doesn't get to it first

    Sent from my SM-G930W8 using Tapatalk
    Mountains cant stop me
    they have tried

  3. #3
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    @jamann: So my plan was destined to fail from the beginning At the time I couldn't really afford a castle BEC + the programming card, but I guess I will have to save up for one (for the time being I could pull out the HW 10A "brick" from my piper). It seems that the receiver needs the ground from the servo, because my friend hast the same truck as mine and he couldn't get it to work without a ground.

    Thanks for the info

  4. #4
    RC Turnbuckle Jr. jamann's Avatar
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    Quote Originally Posted by Madatij View Post
    @jamann: So my plan was destined to fail from the beginning At the time I couldn't really afford a castle BEC + the programming card, but I guess I will have to save up for one (for the time being I could pull out the HW 10A "brick" from my piper). It seems that the receiver needs the ground from the servo, because my friend hast the same truck as mine and he couldn't get it to work without a ground.

    Thanks for the info
    You could use 2 just more wiring to do.
    Just dBl check your wiring before powering

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    Mountains cant stop me
    they have tried

  5. #5
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    Summit BEC across each LIPO - NO NO!!

    a retired old farts 2 cents - don't connect the way you did! - why? - batteries wired in series!
    Great idea, but incorrect application.

    In my Summit, I run dual Savox SV-1271SG Servos, powered by a single Castle 20 amp Regulator (BEC). It has dual outputs set to 7 volts, one for each servo. I have the BEC connected to the battery side of the EVX-2 ESC. Control from Rcvr and ground from BEC & Rcvr are connected to both servos, Positive from BEC only to both servos.

    You need to connect across both batteries, NOT ACROSS EACH! And for both servos, use the same connection even if multiple BEC's. One black and one red wire will not be used from the ESC input wires. But which pair of wires is the question?
    I used the negative from the outside black lead, power switch & light end of EVX-2 ESC. Positive went to the red lead between the motor drive wires. No smoke, and greatly improved steering. Seemed logical they would put the center of a series battery configuration together on the ESC, so the other red & black wires, the ones separated, were my choice. Seems to work OK.

    If I correctly understand the battery configuration, the red & black battery leads next to each other on the ESC should not be used. What Traxxas is doing is running these batteries in series, so these 2 battery wires, next to each other on the ESC, are connected in the ESC, are electrically the same, and neither is ground. Both of these wires will be at the same voltage as a single battery, as measured to the real chassis ground. You put one BEC input ground wire to the same electrical point as the other BEC's input high side. More damage may have occurred than obvious, Rcvr may have suffered.
    Hope that makes sense.

    Have 10 trucks, Grandkids love them.
    The Summit is my favorite, though the Gkids think it is slow.

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