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Isolated battery for the retract or use the airborne packs for the retract ?

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  • Isolated battery for the retract or use the airborne packs for the retract ?

    I’m using a Jeti CB200 in my plane and have been told a separate battery pack for the retract is best so the retract won’t drain the airborne battery. I’ve also been told that the CB200 uses poly fuses so if the retract servo jammed, the fuse for that servo will blow so the airborne battery keeps working and the receiver/servo power is not interrupted by a dead airborne battery. I would like to hear opinions from the experts.
    Thanks !

  • #2
    I'm no expert but I would think if you're concerned about it that it would be easier and lighter to just add a fuse inline with the retract. If you just use a separate battery without a break in the line no telling what would happen.
    I would also guess if you had a dead short/bind it would eventually melt the connections and stop the draw. With a two battery setup, I would think you may crater the number one battery and get a low voltage alert on your telemetry to abort the tow and return as quickly as possible. Of course if you get fire going all is lost anyway. With a separate retract battery would you get a low voltage or overcurrent alert?

    I got to thinking, don't most newer servos have overload protection built in?
    Last edited by BryanB; 01-26-2020, 04:56 AM.

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    • #3
      My auxiliary power system that runs my retract, retract brake, release servo and now my SLS retract servo, is powered by a small nimh battery conditioned through a voltage regulator that powers the servos through a separate receiver designed to be an extension of the primary receiver or as a redundant protection device. The only connection between my aux system and the main flight control system is the data link/signal wire between the two.

      The only problem with depending on built in or inline fuses is when the load isn't enough to trigger the fuse, but is enough to drain your battery before you figure out what's going on.

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      • #4
        Four answers..

        1. In these days of telemetry it is easy to monitor onboard voltage and set alarms
        2. The Emcotech over volt cutoff works very welll. Can be set to cut or continually reset. https://www.hacker-motor-shop.com/Ra...A16000&p=10486
        3. Wire a separate battery
        4. Run a separate receiver setup

        I’ve done them all through the years. Today I simply make certain I have a clean setup and wire the plane as normal.

        John Derstin’s article on separate circuit. http://web.archive.org/web/200407011...tractpower.htm

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        Last edited by Steve P; 01-26-2020, 01:22 PM.
        Team PowerBox Systems Americas... If flying were the language of men, soaring would be its poetry.

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        • #5
          It is good advice to run your retract on a separate isolated battery. My Ventus receiver and flying surfaces are all high voltage and are powered by redundant LiIon batteries. The retract is a 6 V. servo and is powered by a LiFe battery. The diagram that Steve posted above is basically what I use. If the retract jams you will not loose flying surface power. Then again if it stalls the servo one may have the scenario Bryan describes happen.
          Mark

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          • #6
            Thanks to all for the replies. I've decided to go with a dedicated battery for the retract.

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            • #7
              my 2 cents.

              As Steve wrote, there are options.
              When I first started with sailplanes and retracts I used a separate battery for it and followed the schematic above, over time, I got away from the extra weight and annoyance of the battery and went with the Emcotec OCP . Never had an issue.
              Len Buffinton
              Team Horizon Hobby

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              • #8
                I know there is always the possibility of a component failure either through manufacturing or abuse but has anyone ever had a landing gear failure that either shorted out or drew excessive current and drained the battery, caused a telemetry alarm or tripped a fuse? I know we all try to minimize risk but where do we draw the line?

                This has me wondering about having a more indepth discussion of a servo failure that would compromise the entire electrical system.
                Should we install current protection on our high demand servos like flaps and tow release as well? Maybe we should install circuit protection on all our servos?
                Another question I can't seem to find the answer to is what does the built in "over-current" or "temperature" protection on modern Hitec, MKS, Spektrum, etc. servos actually do?

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                • #9
                  All good questions Bryan, but I have read recently of people losing multi thousand dollar F5J gliders because of battery failure. So, some have developed backup battery systems to save an airplane. Obviously since we are having this discussion, electronics and simple solutions were developed because it was perceived as a failure point. Retract systems are the most likely to experience a failure. They can be high load, prone to binding and abused much more than the flying surface systems. Since most scale ships of this size have the room and can carry the weight it is good insurance at a low cost for at least the retract, IMO.
                  Mark

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                  • #10
                    If I remember correctly my high dollar Hitec retract servo has built in over-current protection. But all that means is that it still tries to accomplish the task assigned (up or down) but at a reduced load. As for the Emcotec OCP from Hacker its a good solution for just 30 euros plus about 4 euros VAT plus another 33 euros for shipping to the USA. This bring the total to almost $75 US dollars. That's why I went with the second battery. Well that and I needed another 166 grams up front for C/G so a second battery was an easy decision. But I do like the idea of an inline fuse. Maybe 5 or 7A.

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                    • #11
                      I have always used a separate undercarriage battery, twin house battery's feeding the main RX via a powerbox regulator that powers all other systems the regulator gives fail safe in the case of one battery failure, A separate battery for the motor with its own separate RX.on a Futaba 16sz running the two RX with telemetery

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                      • #12
                        Originally posted by BryanB View Post
                        I know there is always the possibility of a component failure either through manufacturing or abuse but has anyone ever had a landing gear failure that either shorted out or drew excessive current and drained the battery, caused a telemetry alarm or tripped a fuse? I know we all try to minimize risk but where do we draw the line?

                        This has me wondering about having a more indepth discussion of a servo failure that would compromise the entire electrical system.
                        Should we install current protection on our high demand servos like flaps and tow release as well? Maybe we should install circuit protection on all our servos?
                        Another question I can't seem to find the answer to is what does the built in "over-current" or "temperature" protection on modern Hitec, MKS, Spektrum, etc. servos actually do?


                        Hi Bryan,
                        To answer the question directly, YES. Seen it happen a couple times and heard about it a few more.

                        We were at an event and a guy took off normally, but a stick kicked up and jammed the gear. We didn't realize it at first, but then someone commented the gear looks like its hanging down. He tried to cycle the gear but the servo was fried, luckily he got the plane down.

                        Last year at Cumberland, Matt ( on this site) had a retract servo jamb and it fried the entire wire harness all the way to the power safe receiver, which was partially melted too. He got the plane on the ground and thanks to the power safe receiver, he still had a plane to fly another day. Of course the burnt electronic smell lingers on forever.
                        Len Buffinton
                        Team Horizon Hobby

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                        • #13
                          Originally posted by lenb View Post



                          Hi Bryan,
                          To answer the question directly, YES. Seen it happen a couple times and heard about it a few more.

                          We were at an event and a guy took off normally, but a stick kicked up and jammed the gear. We didn't realize it at first, but then someone commented the gear looks like its hanging down. He tried to cycle the gear but the servo was fried, luckily he got the plane down.

                          Last year at Cumberland, Matt ( on this site) had a retract servo jamb and it fried the entire wire harness all the way to the power safe receiver, which was partially melted too. He got the plane on the ground and thanks to the power safe receiver, he still had a plane to fly another day. Of course the burnt electronic smell lingers on forever.
                          That's the info I was looking for. Guess I'll have to figure out how many amps that big gear servo draws in a bind and figure out what fuse to use.

                          Just found on Hitecs website that the HS7954sh I use for my ASH31 gear has a stall amp of 3000mA. So I guess maybe just use a 3amp fuse? Or 2.5 to be safe? Would a short section of 28ga servo wire melt at 3amps?
                          Last edited by BryanB; 01-28-2020, 04:51 AM.

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                          • #14
                            I'm thinking something like this---

                            https://www.amazon.com/2-Pack-Gauge-.../dp/B01MQP96S3

                            Click image for larger version

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                            • #15
                              Thats an option, not the best one but an option.
                              I would highly recommend the Emcotec OCP Steve mentioned above for the following reasons.
                              1) its programmable, so you get to choose the stall point.
                              2) it can be set to shut off completely if it detects a stall. OR better yet, try again in 5 seconds, rtinse and repeat
                              3) does not require modifying anything other than plugging it in.

                              Cost is very reasonable considering the thousands of dollars in the airplane already.

                              Either way, protection is important.

                              Excellent thread BTW
                              Len Buffinton
                              Team Horizon Hobby

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