Page 1 of 2 12 LastLast
Results 1 to 40 of 58
  1. #1
    RC Qualifier
    Join Date
    May 2010
    Location
    Colorado
    Posts
    542

    External BEC to Servo Amp Draw

    Ok. Before you all start telling me to use the search feature, I have been reading threads from many different forums for a while now and can't find a clear answer.
    With a single high torque servo in the Summit, I'm adding an external BEC (CC BEC). The servo I am running is a JR Z9100T. It's only rated to run on 6v, so I basically have two options:

    1. Attach BEC power leads to EVX-2 battery leads in series (14.8v) and then plug the BEC directly into the RX. Disable ESC BEC.

    2. Attach BEC to ESC power leads. Plug black and red JR servo leads into BEC output and white signal wire into RX. Leave ESC BEC enabled.


    I think both of the options is a viable solution, but my question is this:

    Running this JR servo at 6v, is the servo amp draw going to tax the servo connector (option 2) or the receiver (option 1)? I don't know exactly what servo connectors are rated for, but I think it's somewhere around 3 amps. Should I change the servo connectors over to something a little beefier?

    And if it's not an issue for a 6v servo, what about a 7.4v servo? I would hate to fry anything because it was taking too many amps.

    Of course, now that I think about it, is this third option viable? But it still leaves the question of whether the servo connector can handle the current.


    Thank you in advance for all of your input/suggestions/help. I appreciate it.
    Why can't other people share my opinions?

  2. #2
    RC Qualifier
    Join Date
    May 2010
    Location
    Colorado
    Posts
    542
    And I will be happy to give anyone a tutorial on how to use Paint. :P
    Why can't other people share my opinions?

  3. #3
    RC Turnbuckle Jr. jamann's Avatar
    Join Date
    Sep 2009
    Location
    Victoria B.C Canada
    Posts
    5,197
    The simplest way would be disable the on board bec and power the rx with the bec at 6v.if the servo can't use 7.4v then
    Simpler to do it that way.


    Sent using lipo power
    Mountains cant stop me
    they have tried

  4. #4
    RC Qualifier
    Join Date
    May 2010
    Location
    Colorado
    Posts
    542
    With this servo being used in the Summit for crawling applications, is it possible that the servo is going to overdraw amps? Do you think with these higher power servos, the servo connectors/RX can handle the amps?
    Why can't other people share my opinions?

  5. #5
    RC Qualifier
    Join Date
    Apr 2013
    Location
    Ontario, Canada
    Posts
    778
    im awaiting my Savox and a castle BEC with a castle link. I will be trying the 3rd option.

    Id really like to know if the y harness can take the amps too..... I want to power my rx and servo with the external bec.
    To SUMMIT up, its my coolest RC.

  6. #6
    RC Qualifier
    Join Date
    May 2010
    Location
    Colorado
    Posts
    542
    I know that some people use the stock connectors and/or power the rx directly with the BEC while using higher power servos. I'm confident that in most any racing or bashing setup that would work, but I'm concerned about a crawling setup; when the servo is constantly under a lot of stress.
    Why can't other people share my opinions?

  7. #7
    RC Qualifier
    Join Date
    Apr 2013
    Location
    Ontario, Canada
    Posts
    778
    What would you set the BEC to for amps to power RX and servo? mine goes to 10A.
    To SUMMIT up, its my coolest RC.

  8. #8
    RC Turnbuckle Jr. jamann's Avatar
    Join Date
    Sep 2009
    Location
    Victoria B.C Canada
    Posts
    5,197
    On the castle you can't set the amps but can set volts. 6v is what the rx wants.
    It's capable of supplying up to 10 amps if the demand is there.



    Sent using lipo power
    Mountains cant stop me
    they have tried

  9. #9
    RC Qualifier
    Join Date
    Apr 2013
    Location
    Ontario, Canada
    Posts
    778
    Quote Originally Posted by jamann View Post
    On the castle you can't set the amps but can set volts. 6v is what the rx wants.
    It's capable of supplying up to 10 amps if the demand is there.
    Ok, so i want 6v for servo, I also want to run my rx/lights off the external BEC. How many volts should the BEC be set to via my castle link to run it all?
    To SUMMIT up, its my coolest RC.

  10. #10
    RC Turnbuckle Jr. jamann's Avatar
    Join Date
    Sep 2009
    Location
    Victoria B.C Canada
    Posts
    5,197
    6v .The castle will handle the amps being needed.remember if you are powering the rx disconnect the evx bec.
    Also if you are using the LVC model evx
    I would pull power from the existing bec side.Two reasons
    1) The lvc I believe measures that pack for cut off
    2) There have been reports of bad things happening when not taken from the bec side.I believe it is because of how it is wired internally.it pulls bec power from one side then puts the batts in series internally.when done wrong
    Instant melting of the ground wire.
    Not a good time at all.


    Sent using lipo power
    Mountains cant stop me
    they have tried

  11. #11
    RC Qualifier
    Join Date
    May 2010
    Location
    Colorado
    Posts
    542
    Quote Originally Posted by jamann View Post
    6v .The castle will handle the amps being needed.remember if you are powering the rx disconnect the evx bec.
    Also if you are using the LVC model evx
    I would pull power from the existing bec side.Two reasons
    1) The lvc I believe measures that pack for cut off
    2) There have been reports of bad things happening when not taken from the bec side.I believe it is because of how it is wired internally.it pulls bec power from one side then puts the batts in series internally.when done wrong
    Instant melting of the ground wire.
    Not a good time at all.


    Sent using lipo power
    Good info. Thanks a bunch. But let me rephrase my original question:
    How many amps do you think a high torque servo (6v or 7.4v, around 350oz/in torque) would be pulling on average?
    Why can't other people share my opinions?

  12. #12
    RC Turnbuckle Jr. jamann's Avatar
    Join Date
    Sep 2009
    Location
    Victoria B.C Canada
    Posts
    5,197
    My guess a couple amps anyways under full load .i run with a few guys running hitec 7950
    One is stock internal bec no probs
    One is cc bec at 7.4 the other is in the process of going cc bec.so maybe some bec's are better than others in the evx 2
    I'm running a 7955 hitec 333oz of the evx no issues(knock on wood)


    Sent using lipo power
    Mountains cant stop me
    they have tried

  13. #13
    RC Qualifier
    Join Date
    Apr 2013
    Location
    Ontario, Canada
    Posts
    778
    Wonder if I could find a pic of where people solder the BEC`s wire to the esc power wires? on the esc side of the wire? or the battery plug side?
    To SUMMIT up, its my coolest RC.

  14. #14
    RC Turnbuckle Jr. jamann's Avatar
    Join Date
    Sep 2009
    Location
    Victoria B.C Canada
    Posts
    5,197
    I made a harness for mine.
    Female and male traxxas connecters
    As short of wires as I could between them.I did this so I could easily remove it if I wanted or needed to.add it at the plug side as soon as its plugged into a batt it powers up the rx and servos


    Sent using lipo power
    Mountains cant stop me
    they have tried

  15. #15
    RC Qualifier
    Join Date
    Apr 2013
    Location
    Ontario, Canada
    Posts
    778
    Thanks, I may just have to try that. I did get two packs of trx connectors Dont happen to have some kinda pic of it?
    To SUMMIT up, its my coolest RC.

  16. #16
    RC Qualifier
    Join Date
    May 2010
    Location
    Colorado
    Posts
    542
    Jamann did something like this I believe.


    I'm going to wire my BEC to both packs simply for the purpose of draining both packs equally.
    Why can't other people share my opinions?

  17. #17
    RC Qualifier
    Join Date
    Apr 2013
    Location
    Ontario, Canada
    Posts
    778
    Oh Thats a little clearer, Thanks Larsen.

    Guess I should just envision a second batt connected straight to the esc beside the other batt right?

    What really appeals to me as a technician, is that with the tra connecters in the you can disconnect IF you were having troubles and trouble shot without the BEC.

    and you`d have to remove the wire from the esc to the rx.
    To SUMMIT up, its my coolest RC.

  18. #18
    RC Qualifier
    Join Date
    May 2010
    Location
    Colorado
    Posts
    542
    Exactly. The other battery need not be soldered/touched/looked at/thought about. You're only going to wire the BEC into one battery. Make sure to wire it into the BEC side of the ESC though.

    Yes, this solution provides an easily removable setup. A bit more expensive and more soldering though.
    Why can't other people share my opinions?

  19. #19
    RC Turnbuckle Jr. jamann's Avatar
    Join Date
    Sep 2009
    Location
    Victoria B.C Canada
    Posts
    5,197
    Quote Originally Posted by larsen8 View Post
    Jamann did something like this I believe.


    I'm going to wire my BEC to both packs simply for the purpose of draining both packs equally.
    That is exactly it.thank you for the pic
    It explains it better than it can be explained.


    Sent using lipo power
    Mountains cant stop me
    they have tried

  20. #20
    RC Qualifier
    Join Date
    Apr 2013
    Location
    Ontario, Canada
    Posts
    778
    So now I just need like 2 inches of wire for between the TRX connectors... An order for 2" lol. Im sure I can come up with some more things...
    To SUMMIT up, its my coolest RC.

  21. #21
    RC Turnbuckle Jr. jamann's Avatar
    Join Date
    Sep 2009
    Location
    Victoria B.C Canada
    Posts
    5,197
    I used some from a dead Nimh as it didn't need it anymore lol


    Sent using lipo power
    Mountains cant stop me
    they have tried

  22. #22
    RC Qualifier
    Join Date
    Apr 2013
    Location
    Ontario, Canada
    Posts
    778
    What gauge would be best?
    To SUMMIT up, its my coolest RC.

  23. #23
    RC Turnbuckle Jr. jamann's Avatar
    Join Date
    Sep 2009
    Location
    Victoria B.C Canada
    Posts
    5,197
    I used 12 gauge I believe,May have been 14.anything bigger is tricky to do when they are that short(getting them on the connecter)pretty stiff and hard to bend and maneuver.


    Sent using lipo power
    Mountains cant stop me
    they have tried

  24. #24
    RC Qualifier
    Join Date
    May 2010
    Location
    Colorado
    Posts
    542
    To whom it may concern:
    I just wired a BEC into an Axial Wraith via this setup. The servo is running on 7.4v and all seems to be working well.
    Why can't other people share my opinions?

  25. #25
    RC Qualifier
    Join Date
    Apr 2013
    Location
    Ontario, Canada
    Posts
    778
    Quote Originally Posted by larsen8 View Post


    I'm going to wire my BEC to both packs simply for the purpose of draining both packs equally.
    Im using this method this weekend. Could I make two harnesses, one for each battery, then the bec would draw power from both batteries?

    Also, could the bottom of htis pic be finished so I can see where the wire needs to be disconnected to disable the evx-2`s BEC?
    To SUMMIT up, its my coolest RC.

  26. #26
    RC Turnbuckle Jr. jamann's Avatar
    Join Date
    Sep 2009
    Location
    Victoria B.C Canada
    Posts
    5,197
    The red wire.if you use a pin you can carefully remove the wire from the plug
    Tape it up can go back to stock again if you want or need to.
    Be very careful. People have fried the ground wire on the esc the two sets of inputs are wired in series internally.
    I believe you are shorting the circuit if hooked up the wrong way.So research that a bit more, so you are sure it will work the way you want it to


    Sent using lipo power
    Last edited by jamann; 04-26-2013 at 10:05 AM.
    Mountains cant stop me
    they have tried

  27. #27
    RC Qualifier
    Join Date
    Dec 2011
    Location
    Arkansas
    Posts
    522
    I found a real clean way to hook the CC BEC up. I bought a pack of Traxxas female connectors (TRA3080) and soldered one of them to the power leads of the BEC. Then I bought a Traxxas Y-Harness (TRA3064) and attached one of the leads to the CC BEC and the other to battery on the BEC side of the ESC.

    Like jamann said ^ drop the red wire that plugs into the receiver and you are good to go.
    SUMMIT, SUMVO, ERBE, EMAXX & REVO 3.3

  28. #28
    RC Qualifier
    Join Date
    Aug 2012
    Location
    Alberta Canada
    Posts
    895
    Quote Originally Posted by larsen8 View Post
    2. Attach BEC to ESC power leads. Plug black and red JR servo leads into BEC output and white signal wire into RX. Leave ESC BEC enabled.




    Quote Originally Posted by larsen8 View Post
    Jamann did something like this I believe.


    I'm going to wire my BEC to both packs simply for the purpose of draining both packs equally.
    I'm not an electrician but i'm pretty sure this isn't going to drain a battery any different. When connected in series both batteries providing equal internal resistance will drain equally. If connected in parallel you would have to wire as shown in the second picture.


  29. #29
    RC Qualifier
    Join Date
    Apr 2013
    Location
    Ontario, Canada
    Posts
    778
    Quote Originally Posted by BlackSheep800 View Post
    I found a real clean way to hook the CC BEC up. I bought a pack of Traxxas female connectors (TRA3080) and soldered one of them to the power leads of the BEC. Then I bought a Traxxas Y-Harness (TRA3064) and attached one of the leads to the CC BEC and the other to battery on the BEC side of the ESC.

    Like jamann said ^ drop the red wire that plugs into the receiver and you are good to go.
    Any chance your a MS Paint pro? feel like drawing me a pic of what your refering to?
    To SUMMIT up, its my coolest RC.

  30. #30
    RC Qualifier
    Join Date
    Dec 2011
    Location
    Arkansas
    Posts
    522
    Quote Originally Posted by Northern Adventurer View Post
    Any chance your a MS Paint pro? feel like drawing me a pic of what your refering to?
    Hope this helps.

    Last edited by BlackSheep800; 04-26-2013 at 12:37 PM.
    SUMMIT, SUMVO, ERBE, EMAXX & REVO 3.3

  31. #31
    RC Qualifier
    Join Date
    Apr 2013
    Location
    Ontario, Canada
    Posts
    778
    Quote Originally Posted by BlackSheep800 View Post
    Hope this helps.


    Great, Thanks. You do have paint skills LoL.

    But if i was to use that set up with the evx2(2 sets of batt leads) and 2 batts, how could it be done? I like the idea of using the pre-made Traxxas y-harness.

    Thanks for the help All!
    To SUMMIT up, its my coolest RC.

  32. #32
    RC Qualifier
    Join Date
    Dec 2011
    Location
    Arkansas
    Posts
    522
    I believe this is more accurate.......sorry.

    SUMMIT, SUMVO, ERBE, EMAXX & REVO 3.3

  33. #33
    RC Qualifier
    Join Date
    Dec 2011
    Location
    Arkansas
    Posts
    522
    Quote Originally Posted by Northern Adventurer View Post
    Great, Thanks. You do have paint skills LoL.

    But if i was to use that set up with the evx2(2 sets of batt leads) and 2 batts, how could it be done? I like the idea of using the pre-made Traxxas y-harness.

    Thanks for the help All!
    I hooked up the Y Harness to the battery that was powering the internal BEC in the EVX2. The other battery still hooks up to the ESC as normal.

    Basically all you are doing (to my understanding) it manually turning off the internal BEC and hard wiring a bigger BEC into the system. Again, from my understanding only one battery operates the electronics (servos) as it comes.

    Someone please correct me if I am wrong.
    SUMMIT, SUMVO, ERBE, EMAXX & REVO 3.3

  34. #34
    RC Qualifier
    Join Date
    Apr 2013
    Location
    Ontario, Canada
    Posts
    778
    Yes, your right, stock esc pulls juice for bec ftom 1 batt. I was just hoping to use your diagram, while drawing bec power from both batteries so they drain evenl
    To SUMMIT up, its my coolest RC.

  35. #35
    RC Qualifier
    Join Date
    May 2010
    Location
    Colorado
    Posts
    542
    Can someone please explain to me the difference, if any, between 1 and 2? As I understand it, both could be used to power both the RX and the servo.

    Why can't other people share my opinions?

  36. #36
    RC Turnbuckle Jr. jamann's Avatar
    Join Date
    Sep 2009
    Location
    Victoria B.C Canada
    Posts
    5,197
    The difference in the pics is #1 it is powering just the servo
    #2 it is powering the whole system internal bec is deactivated.(red power wire disconnected)
    The first pic is a little confusing the bec power does not go anywhere near the rx.it goes to the servo only.the only wire is from rx to servo(signal)to tell the servo when to do what,with the power
    It is already receiving.the internal bec powers everything else except that servo.


    Sent using lipo power
    Last edited by jamann; 04-26-2013 at 11:49 PM.
    Mountains cant stop me
    they have tried

  37. #37
    RC Qualifier
    Join Date
    May 2010
    Location
    Colorado
    Posts
    542
    So how exactly is #1 powering only the servo and #2 is powering both? Not being rude, just don't know. I know very little about electronics but this baffles me. In both pictures there are power wires going from BEC to RX, so wouldn't the RX be powered by the BEC in both cases (without taking into consideration the ESC wiring).

    Because the BEC signal wire is unneeded for operation, it has been removed in both cases.

    For the Wraith that I mentioned above, I wired in the BEC using #1 minus the red BEC-to-RX wire. That left a black and signal wire coming from the RX.
    I'm not trying to be contentious, but the way I see it, the only difference is that #1 sends power from the BEC to RX and servo simultaneously and #2 sends power first to RX and then from there to the servo.

    A couple more related questions:
    - Is it possible to plug a Y harness into the receiver and then plug the BEC into one output and anything else to the other output (servo or ESC)? Would that power everything?
    - Can you power one Y harness output from the other? For example, if I plugged in a battery into one output of a Y harness, could it power say, a servo, plugged into the other with the input unplugged? I'm pretty sure it could.

    I've been told that it's not possible to power both the RX and a servo with a Y harness. That doesn't seem right.

    Kind of unrelated, but what if I take this:


    And quite literally, cut out the wires highlighted in blue...


    Don't I end up with a perfect BEC-to-servo, RX bypassing harness?
    Why can't other people share my opinions?

  38. #38
    RC Turnbuckle Jr. jamann's Avatar
    Join Date
    Sep 2009
    Location
    Victoria B.C Canada
    Posts
    5,197
    Sorry got busy,the first diagram
    Shows bec power to rx (6v?)
    Bec power to servo 6v?)
    That is redundant.not needed as the rx is getting a clean 6v with the amps available from the bec.
    If you wanted 7.4 v to the servo only
    Power and ground from bec to servo
    Just need signal from rx to servo
    So to power a high torque servo at 6v no need to wire power to the servo.



    Sent using lipo power
    Mountains cant stop me
    they have tried

  39. #39
    RC Qualifier
    Join Date
    May 2010
    Location
    Colorado
    Posts
    542
    I'm really just going on theory here. At this point I'm no longer concerned about specifics like ESC wiring, voltage, etc. I'm trying to figure out what works and what doesn't. I already know how I'm going to wire the BEC into my Summit. But I've got so much engineer blood in me that I want to know how and why things work the way they do.
    Why can't other people share my opinions?

  40. #40
    RC Enthusiast
    Join Date
    Jul 2012
    Location
    Grand Rapids
    Posts
    28
    [QUOTE=jamann;5488869]6v .The castle will handle the amps being needed.remember if you are powering the rx disconnect the evx bec.
    Also if you are using the LVC model evx
    I would pull power from the existing bec side.Two reasons
    1) The lvc I believe measures that pack for cut off
    2) There have been reports of bad things happening when not taken from the bec side.I believe it is because of how it is wired internally.it pulls bec power from one side then puts the batts in series internally.when done wrong
    Instant melting of the ground wire.
    Not a good time at all.


    yeah all you have to do is touch the black wire with it plugged into the rx and poof up in smoke i know i did it twice stupid me first i thought that something else was wired wrong oh ok ill get a new esc because it melted the wire in half, next just touched the black wire to test it and poof on my new one did not break the wire but melted the coating pretty good so in comes the heat shrink and has been working fine
    rustler vxl, bandit vxl, summit, t-maxx, rally

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •