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Help with bec choice please

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  • Help with bec choice please

    I have a 6s powered warbird type with no retracts but seven standard size digital servos ( futaba 3152, 6.2kg of torque on 6v). I am wondering about the simplest way to power these servos and rx. I would like to use a separate bec but would like to know what size do I need? It would be great to be able to just plug in the flight battery and fly rather than have extra rx batteries and switches. Is it ok to use just a separate bec or do I have to use a back up battery aswell?
    I will be grateful for any replies.

  • #2
    I'm surprised that nobody has jumped in to help you as there are lots of knowledgeable people here. Usually, after I post up something, somebody comes along to add in their thoughts to do it better or differently. I don't know why that is, so here goes and I'm sure you'll get other comments soon.

    The simplest way to do it is to get an ESC that is big enough and is compatible with the power system you are using (IE, motor, prop, weigh of plane) that also has a built in BEC. However, you've indicated that you want to go with an external BEC ("separate" as you call it). But then, you don't wish to have the hassle of "extra" batteries to power it. If you don't want the "simplest" way as I already mentioned, then you get an external BEC that can handle 6s power as an input and be able to put out the necessary 5 to 6v needed to push through the RX. My rule of thumb for servo needs, is about 1/2 amp per servo but it's rare that you would be driving all of the onboard servos at the exact same time (unless you are also using a gyro and even then, there's still enough reserve to make it work). I've used external BECs in some planes like the kind purchased from HobbyKing where I've soldered the power leads to the ESC connector. That way, when you plug in the flight battery, it also powers the BEC. Although I use the cheap $5.00 ones from HK, you can find a suitable one at Motion: I've never had a cheap one fail yet.
    If you don't like the idea of splicing the BEC into the ESC plug, then you must go with an auxiliary battery that will push the proper volts into the BEC. I'm not sure what you consider a "back up" battery but for me, a back up battery is one that does nothing till it's needed. Something like this: I used to use one but after a while, it got to be a bit of a nuisance as most of today's BECs (both internal and external) are very good and reliable. I mean, how many "back ups" is enough to give you peace of mind?


    • #3
      I've used several of these with multiple servos, retracts and lights and never had any issues. I connect it to the ESC end of the battery leads.
      TiredIron Aviation
      Tired Iron Military Vehicles


      • #4
        Thanks xviper for your helpful thoughts on this.
        Thanks TiredironGRB for your link to the ccbec.
        Useful information to think about.
        I also contacted Motion rc tech department and was very impressed with the speed of reply. I don't think I would hesitate in purchasing from this supplier. They suggested the ZTW 18amp or ccbec 20 amp would have a bit of headroom in case of a worst case scenario. Although I realise I counted the servos wrong! I have 5 digitals and 1 analogue in the plane. I have a ZTW 10 amp peak I could use or a YEP 20 amp new in packet and so could use one of these?
        Thanks again


        • #5
          Chippy...........welcome to the Squawk
          The ZTW 10A UBEC you mention is a great device, I have it in several larger warbirds (HSD 1600 Skyraider and FMS 1700 Tigercat for example)
          I like the ZTW devices because you can have adjustable higher output voltages. This is an absolute necessity when using a backup power source like the Scorpion BU Guard as XViper has suggested.
          I use the Scorpions in all my more expensive($500+) warbirds.
          The Scorpion requires a system voltage of at least .5Vdc(half volt) higher than it's turn on voltage of 5Vdc. This is where the ZTW's adjustable output voltage shines whereas I set it for 5.5 or 6 depending on the type of servos being used.
          The adjustable voltage is done mechanically with a jumper.
          The Castle device mentioned by TiredIron is a good device but........... the voltages are only adjustable via a separately sold Castle Link USB interface.
          Hope you find this helpful also.
          Best regards,
          Warbird Charlie
          HSD Skyraider; FlightLine: Sea Fury; FMS 1400: P-40B, P-51, F4U, F6F, T-28, P-40E, 1700 F4U & F7F and a Fox glider; Freewing: A-6, P-51; VQ: P-39; Dynam: ME-262, FW-190, Waco; ASM A-26; ESM F7F-3; LX PBJ-1 EFL CZ T-28, C-150


          • #6
            Thanks OV10, good point regarding the need/cost of the extra lead for the Castle Creations (although they do get very favourable feedback). I am leaning towards a ZTW at the moment and may get a 12amp/ 18 amp peak to be on the safe side and will be a useful size to have for future use.


            • #7
              chippy Both OV-10 and TiredIron make good points and recommendations. You can't go wrong with either as long as you know what you're getting into. The one thing I'll add is to ensure your solder joints from your UBEC to your main power wires are done properly. UBECs are worthless once those solder joints fray and falter --ask me how I know!