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Official Freewing MiG-29 Fulcrum Twin 80mm Thread

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  • Interesting….I did more research. The general opinion is that it’s fine. Here is a video experiment + measurements.

    Everyone online keeps telling me this isnt possible. You cannot run different capacity cells in parallel. Im not sure what they think will happen but I can a...


    Apparently the lower internal resistance (higher capacity) battery will supply the most current while the lower capacity battery….now having higher internal resistance after running….will back off and supply the lesser amount of the total current.

    Of course, the battery voltages are equal always.

    The precaution is….The two batteries charged voltages should be close before connecting.

    Learned something!!!! Anyone finding differently? There are folks like me that say don’t….but their comments are usually followed with a lot of discussion + reasons why it is OK.

    -GG

    Comment


    • He is correct. Since the batteries are in parallel they will maintain the same voltage and the ESCs will draw more power from the larger battery so they reduce in voltage at the same rate. The larger battery will supply more Watts or Ah but that's fine as long as the true C rating can handle the draw on it.

      I don't see what internal resistance has to do with it. Unless they were massively different.

      To compare it to liquid fuel tanks isn't very good unless you make a few assumptions. Because of header pressure they would have to be set up evenly in height so one doesn't drain faster. But if you got that and you had output lines that where large enough to handle the flow from each you would see them drain evenly with the larger tank supplying more volume than the smaller one. Think of the volume in these tanks as the Ah that the batteries have.

      But again, he would need a -H- type connection between the two batteries and the two ESCs and while it would work it would be better to stick with the stock set up of separate equal sized batteries to each ESC,

      Comment


      • Not an example of 2 different capacity batteries but ......................... I recently ran twin batteries in my F-14 Tomcat. Both were 5000mah, 6s. One was 60C and the other was 45C. Interestingly, the 60C drained faster. Not science, just an observation. I also do the same in my Mig 29 but never took note of the measured differences at the end of the flight. I'll do that from now on.
        (Although a different scenario where different electrical properties exist, I've run 6000mah, 6s and 6000mah, 2s in one of my 8s planes. Both are the same "C" rating and both drained down at the same rate. Like I said, this is a "series" set-up as opposed to a parallel set-up.)

        Finally, I don't think anyone said it couldn't be done. It obviously can be done. I think the question is ........................ Does one draw down the smaller battery faster and potentially take it closer to its danger point? That video didn't address that. He didn't run them down to see if one or the other went dead first.

        Comment


        • Two separate set ups will not drain exactly the same. The two motors/ ESCs may draw different amounts of power and/ or the batteries could be more or less efficient. Most of the times we won't see it unless we have something like afterburner lights, sound systems or other draws on only one side.

          On the MiG you'll see the battery supplying the BEC drain faster with everything else being equal.

          The 8S, a 6S + 2S, set up has a big potential for battery issues if you don't use fairly matched cells. When I don't use the same sized packs I use larger packs on the 2S side, example a 5200 40C 6S with a 5800 30C 2S. This has the potential of the larger battery going lower in use than the smaller one and if run down to where it could cause a problem the Ah capacity would be higher than the 2S so I wouldn't have a sharp drop off in voltage like I would the other way around. Hope that makes sense. With 6+2 (or any mismatched SERIES set up it's very important to look at your cell voltages after the flight to make sure the two packs are working well together and if you see that they aren't (especially if the 2S has much lower per cell voltages don't use it as part of the 6+2.

          Comment


          • His question was whether or not the ESCs were connected in parallel or separately. He said that if they were in parallel he would use a 5000 and 4000 battery. He also said that if they were separate he would use batteries of equal capacity.

            As for batteries....
            Any two or more LiPo batteries connected in series must be the same capacity but can be different voltage. EG, you can do a 6s and a 2s in series to get an 8s pack but the batts must be the same mah capacity.

            Any two or more LiPo batteries connected in parallel must be the same voltage but may be different capacity. EG, you can connect a 6s 5000 in parallel with a 6s 1000 to get a 6s 6000 pack. As the pack discharges or charges the voltage between the batteries remains the same throughout. This means that the smaller capacity battery will reach it's full discharge/charge level at the same time as the larger capacity battery

            https://www.radiocontrolinfo.com/par...rplanes-boats/
            Parallel Wiring Quick Tips
            • Only wire packs in parallel that have the same voltage
            • It is a good idea to wire packs in parallel that are around the same age and condition (otherwise power will be split based on health of the battery where the healthier pack delivers more)
            • The C rating of a battery pack does not double, the battery capacity doubles
            Series Wiring Quick Tips
            • Wire packs that both have the same capacity (mAh) and C rating
            • Packs wired in series must be around the same age and condition (Otherwise the least healthy pack will be pushed harder)

            Comment


            • Originally posted by hilldebrandt View Post
              Hmmmm....If he knew so much about batteries, why did he even ask a question.
              The question was actually about whether the wires were already connected or went to separately to the left and right ESCs.

              Comment


              • Yes to all that...

                And answered 11 minutes later :)

                Originally posted by dabevan View Post

                The question was actually about whether the wires were already connected or went to separately to the left and right ESCs.

                Comment


                • Originally posted by dabevan View Post

                  The question was actually about whether the wires were already connected or went to separately to the left and right ESCs.
                  I apologize...I was being a smart***. I've edited out that comment in my original post.

                  Comment


                  • Originally posted by xviper View Post
                    Do you have science or electrical facts to support your claim? If not, I don't think he's wrong and since I don't have any science to back that up, his statement holds just as much credibility as yours. In fact, I'm in agreement with GG.
                    Take 2 fuel tanks, 1 is 10 gallons and the 2nd one is 12 gallons. Each feeds an identical engines running at the same time at the same throttle. Which do you think will run out of fuel first? In the case of LiPo batteries, which one do you think will get to it's LVC first and possibly damage that battery? During this time, the bigger battery keeps running the first engine. True, if you gauge your flight time according to the lowest common denominator, the smaller battery, and stop flying before it can get to its danger level, then fine, neither battery gets damaged.
                    So please, tell us how batteries work.
                    I have a degree in Electronic and Electrical Engineering and 25 years of engineering experience.

                    Two batteries in parallel will have their voltages pinned to each other as the two pos+ will be connected and the two neg- connected. Therefore it is impossible for one to discharge more than the other one. What will happen in practice is that in order to keep this voltage the same the larger pack will supply more current than the smaller pack.

                    Your example with fuel tanks is not parallel, it's separate tanks feeding separate engines. If it was parallel then the two tanks would be connected to each other via a pipe at the bottom of the tank. In this instance both tanks would empty at the same time.

                    I hate to appear rude, but either you understand and accept what I've said above, or you don't, but I know what I'm talking about.

                    Note, the original question wasn't asking about batteries, I wanted someone to confirm whether the leads were connected somewhere in the fuz I couldn't see (ie in parallel) or went to separate ESPs - this is the equivalent of your fuel tanks going to separate engines or being connected by an out of sight pipe.


                    Regards

                    Dave

                    Comment


                    • Originally posted by xviper View Post
                      Does one draw down the smaller battery faster and potentially take it closer to its danger point?
                      NO! THEY ARE ALWAYS AT THE SAME VOLTAGE AS THEIR POS+ AND NEG+ TERMINALS ARE CONNECTED TO EACH OTHER!!!!! 🤯

                      Comment


                      • Hi Dave….

                        Confirmed! Each MiG-29 power/battery connector goes to its own separate ESC. And the BEC connects to only one battery.

                        I learned something in these recent posts!

                        I haven’t noticed any significant difference in the draw down between the two separate batteries. But I only pull about 4000 mAh outa each (6000) battery. Might be more significant with longer flights.

                        -GG

                        Comment


                        • Originally posted by dabevan View Post

                          NO! THEY ARE ALWAYS AT THE SAME VOLTAGE AS THEIR POS+ AND NEG+ TERMINALS ARE CONNECTED TO EACH OTHER!!!!! 🤯
                          But what if they aren't? In the Mig29, doesn't one battery power one ESC/motor and BEC while the other powers the other ESC/motor? Except for having the throttle leads "Y'd", the power from one battery doesn't mingle with the power from the other. Their + and - terminals are not connected to each other.

                          BTW, I've always been talking about the Mig29 application, not about some other plane that might have their systems in parallel.

                          Comment


                          • Then you are not talking about what the rest of us and he was asking about.

                            Comment


                            • Originally posted by Evan D View Post
                              Then you are not talking about what the rest of us and he was asking about.
                              But this is a Mig29 thread. Was he talking about a Mig29 when he was telling us about a parallel system where two different battery sizes will drain at the same rate? What I got out of it was that if you had one battery smaller in mah than the other in a Mig29, he's telling me that both will drain in a way that both will run out of juice at the same time. Is this true?

                              Comment


                              • If connected in parallel, as he was talking, yes…

                                Comment


                                • Originally posted by xviper View Post
                                  But this is a Mig29 thread. Was he talking about a Mig29 when he was telling us about a parallel system where two different battery sizes will drain at the same rate? What I got out of it was that if you had one battery smaller in mah than the other in a Mig29, he's telling me that both will drain in a way that both will run out of juice at the same time. Is this true?
                                  Edited for clarity…

                                  That’s what I understood. But, I also did additional research and confirmed others have mixed different capacity batteries in systems like the MiG set-up without issue while also CONNECTING THE BATTERIES IN PARALLEL.

                                  Not an intuitive result, for sure. But…apparently valid.

                                  -GG

                                  Comment


                                  • Originally posted by GliderGuy View Post

                                    That’s what I understood. But, I also did additional research and confirmed others have mixed different capacity batteries in systems like the MiG set-up without issue. Not an intuitive result, for sure. But…apparently valid.

                                    -GG
                                    Here is where I got confused. Remember, I'm always thinking "Mig29". So, is the Mig29 a parallel system or not? Since the two systems aren't sharing batteries, then it's NOT a parallel system, right or wrong? If it's not a parallel system, then running two different sizes of batteries would result in the smaller battery crapping out first, right or wrong? If one craps out first, a problem could arise (ie, not a good idea), right or wrong?
                                    Sure, we learned something but is that something applicable to the Mig?

                                    Comment


                                    • Stock no but his context was to make it a parallel set up…

                                      If, as GG says people have mixed different sized packs on the stock set up and lived they just didn’t fly long enough to drain the smaller battery.

                                      Comment


                                      • Originally posted by Evan D View Post
                                        Stock no but his context was to make it a parallel set up…

                                        If, as GG says people have mixed different sized packs on the stock set up and lived they just didn’t fly long enough to drain the smaller battery.
                                        I intended to state others have PARALLELED batteries on similar systems as the MiG. Hopefully this clears up my statements.

                                        Sorry that I wasn’t more clear.

                                        If you leave the MiG stock….without paralleling the battery connections…and mix different capacity batteries, that would be a disaster in the making.

                                        I went back and edited my original post. My bad!

                                        -GG

                                        Comment


                                        • Just to be clear (again) my original question was asking *if* the MiG was wired in parallel - in which case I was going to run different sized packs (which is perfectly OK!) *if* it's not parallel (which people are saying it's not) then I'll either run identical packs or solder the wires so they are parallel.

                                          I was *never* suggesting running two different pack sizes in a non-parallel set up. (that would be silly.)

                                          I was *never* asking if two parallel packs could be different sizes, as I already know the answer (yes they can)

                                          ...thanks for the replies though!

                                          Dave

                                          Comment

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