blowing caps 180esc

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  • 785boats
    Wet Track Racing
    • Nov 2008
    • 3169

    #46
    I'll see if I can shed some more light on this 'generator' problem.
    In posts # 29 & 30, sundog & Disar got it spot on.
    When you release the throttle at 30,000revs & say 60mph, the motors own inertia & the water flowing over the prop keep the revs up higher & for longer. Yes the motor is slowing down from the moment you release the trigger but it takes a lot longer than it does for a dry run on the bench. But the highest voltage is generated in the first instant that you chop the throttle.
    It must be remembered that this really becomes a problem with ESC's that have a BRAKE mode, as many of the car & aircraft ESC's that a lot of us use, do. If the 'BRAKE' is programmed to the ON mode, a lot of ESC's apply an amount of brake automatically, without you actually pushing the trigger into the brake zone on the Tx.
    This is where the problem arises. Especially if the battery voltage is already at the max (or close to) limits of the ESC.
    If you didn't read the PDF I posted earlier in this thread here it is again. It's interesting reading.
    Cheers.
    Paul.
    Attached Files
    See the danger. THEN DO IT ANYWAY!!!
    http://forums.offshoreelectrics.com/...hp?albumid=319
    http://forums.offshoreelectrics.com/...hp?albumid=320

    Comment

    • ScarabChris
      Senior Member
      • Oct 2010
      • 752

      #47
      I don't buy the generator problem, especially for these Leopard 5692's. You need a good amount of force to turn them by hand so I doubt the water flow will spin the props.

      Comment

      • sundog
        Platinum Card Member
        • Feb 2009
        • 878

        #48
        Originally posted by ScarabChris
        I don't buy the generator problem, especially for these Leopard 5692's. You need a good amount of force to turn them by hand so I doubt the water flow will spin the props.
        You could easily prove or disprove the 'will a high cogging motor (difficult to turn by hand) spin in fast water?' theory by running a real boat 40 or so mph (I consider that as fast when I'm on most boats) and set the transom of your rc boat down in that water. Do you still think it won't spin? If not, then I can see I'm not going to be any help here! .
        Legend 36 sailboat, KMB Powerjet Ed Hardy Viper, ABC jet pwrd BBY Oval Master, ABC Hobby Jetski, NQD Tear Into's, HK Discovery 500, MickieBeez pwrd Jet Rigger!, Davette/Gravtix jet sprint, KMB Powerjet Pursuit, NQD pwrd Jet Catamaran!,Steam pwrd African Queen, Sidewinder airboat, Graupner Eco Power

        Comment

        • BakedMopar
          No Mo Slipah
          • Sep 2009
          • 1679

          #49
          Originally posted by ScarabChris
          I don't know....I guess I'm old school and these ESC's are new technology. I was following the common sense that if the motor is turning less RPM's then its using less power thus putting less load on the ESC. So if I run my boat at low speed the batteries should last longer and the ESC stay cooler.

          But from what I am reading here is seems that if I run the boat at full throttle the batteries will last longer the the ESC's will stay cooler then if I just tool around at low or half throttle.

          Again thats just my old school theory.

          I went ahead and ordered some cap banks for my 54" Fountain as they were getting super hot....at full throttle.
          I have done actual testing on runs with partial throttle to see it's ineffeciency. If you have a data logger do some real world testing and you'll see the outcome. I did two runs with boat setup running at 100% for a baseline and two runs with the speed controller limited to 75%. The partial throttle runs was less effecient by 5% average and temps around the same of 5% increase. Now before any body want to disagree this was done only for my testing and results may vary from boat to boat. I don't have the actual data file as my compy crashed a few months back but this is what I have writen down.
          If all of your wishes are granted, many of your dreams will be destroyed!

          Comment

          • ScarabChris
            Senior Member
            • Oct 2010
            • 752

            #50
            Originally posted by sundog
            You could easily prove or disprove the 'will a high cogging motor (difficult to turn by hand) spin in fast water?' theory by running a real boat 40 or so mph (I consider that as fast when I'm on most boats) and set the transom of your rc boat down in that water. Do you still think it won't spin? If not, then I can see I'm not going to be any help here! .
            No way the props will turn if I lower them in the water at 40 MPH. With the motor in your hand and no coupler on the shaft you almost can't even turn it by hand.

            Comment

            • Rumdog
              Fast Electric Addict!
              • Mar 2009
              • 6453

              #51
              I agree with Chris here. The water isn't even traveling in proper direction to initiate a spinning motion of the props.

              Comment

              • sundog
                Platinum Card Member
                • Feb 2009
                • 878

                #52
                Originally posted by Rumdog
                I agree with Chris here. The water isn't even traveling in proper direction to initiate a spinning motion of the props.
                Rumdog, could you elaborate?
                Legend 36 sailboat, KMB Powerjet Ed Hardy Viper, ABC jet pwrd BBY Oval Master, ABC Hobby Jetski, NQD Tear Into's, HK Discovery 500, MickieBeez pwrd Jet Rigger!, Davette/Gravtix jet sprint, KMB Powerjet Pursuit, NQD pwrd Jet Catamaran!,Steam pwrd African Queen, Sidewinder airboat, Graupner Eco Power

                Comment

                • 785boats
                  Wet Track Racing
                  • Nov 2008
                  • 3169

                  #53
                  Guys.
                  We're not talking about spinning a motor up from zero revs using the prop like a turbine. We're talking about keeping a motor spinning a bit longer when you release the throttle at 30,000 revs.
                  Do your motors stop dead when you release the throttle at full revs? No they don't. The inertia of the armature PLUS the turbine effect of the prop travelling through the water at 40 or 50 mph keep it spinning for a few of seconds acting as a generator. As electricity travels at 186,000 miles per second, it takes nano seconds for it to travel down 4" of wire to the ESC. That is when the damage is done. Especially if the brake mode is ON.
                  If you read the PDF file I posted in my previous thread you will see in fig 3. that with a 6 cell battery & an 80A load, under braking an extra 17.5 volts was generated. If a 6s ESC was being used (that is, rated to 30V) it just had 42 Volts rammed into it with a generated load of 80A, leaving the boat owner wondering why the ESC mysteriously failed.
                  Again I stress that this is mainly a problem when the Brake Mode is switched on & the ESC has automatic braking. But it does happen to a lesser extent with any ESC without the braking mode.
                  That's why it's always best to use an ESC with a higher voltage rating than you are actually using.
                  That's as clear as I can make it i'm afraid.
                  Paul.
                  See the danger. THEN DO IT ANYWAY!!!
                  http://forums.offshoreelectrics.com/...hp?albumid=319
                  http://forums.offshoreelectrics.com/...hp?albumid=320

                  Comment

                  • Rumdog
                    Fast Electric Addict!
                    • Mar 2009
                    • 6453

                    #54
                    I dont believe that. I'm sorry. When I let off throttle, the water is not going to keep the prop spinning for a longer period than when on the bench. Maybe even less spinning.Forward momentum of water on the backside of the prop wont encourage rotation.

                    Comment

                    • 785boats
                      Wet Track Racing
                      • Nov 2008
                      • 3169

                      #55
                      Rumdog.
                      It's OK if you can't believe it so forget about the prop/turbine/generator thing & believe that the motor is still spinning when you release the trigger. True? At that instant it is a generator.
                      The water isn't even traveling in proper direction to initiate a spinning motion of the props.
                      But i think you should have a closer look at your props if you believe that statement.
                      The water flow may be acting against the back side of the prop but it will still spin it in the same direction that the motor was spinning it.
                      Read post #30 again.
                      But this is getting a bit off topic. The initial post was about why ESC's fail & caps blow. I just offered this as one of the reasons. There are lots of reasons & others have offered them too.
                      All the best.
                      Paul.
                      See the danger. THEN DO IT ANYWAY!!!
                      http://forums.offshoreelectrics.com/...hp?albumid=319
                      http://forums.offshoreelectrics.com/...hp?albumid=320

                      Comment

                      • Rumdog
                        Fast Electric Addict!
                        • Mar 2009
                        • 6453

                        #56
                        I will refer you back to post #39 then. Which I believe all to be true.

                        Comment

                        • domwilson
                          Moderator
                          • Apr 2007
                          • 4408

                          #57
                          The main reason caps blow is too much ripple current on the battery side.
                          Government Moto:
                          "Why fix it? Blame someone else for breaking it."

                          Comment

                          • 785boats
                            Wet Track Racing
                            • Nov 2008
                            • 3169

                            #58
                            Read the PDF file.
                            The generated voltage gets ADDED to the battery voltage in the ESC.

                            I install VSD,s in industrial plants. rated at up to 500 Amps & 415 Volts Ac
                            The manufacturers install big chokes, capacitors & electronics to deal with the back EMF generated as the pump or fan or blower winds down under dynamic braking.
                            This voltage is then redirected back into the electrical system.
                            Our ESC's are very basic VSD,s Trust me, the generated voltage is a real thing.
                            I'll let it go now.
                            Paul
                            Attached Files
                            See the danger. THEN DO IT ANYWAY!!!
                            http://forums.offshoreelectrics.com/...hp?albumid=319
                            http://forums.offshoreelectrics.com/...hp?albumid=320

                            Comment

                            • domwilson
                              Moderator
                              • Apr 2007
                              • 4408

                              #59
                              I just couldn't get past "Because the direction of the current flow is now opposite, also voltages caught on
                              resistances
                              in the circuit have opposite polarity and they are thus added to the voltage of the battery." part. Been doing electronics for years and I'm not understanding that part.
                              Government Moto:
                              "Why fix it? Blame someone else for breaking it."

                              Comment

                              • m4a1usr
                                Fast Electric Addict
                                • Nov 2009
                                • 2038

                                #60
                                Originally posted by 785boats
                                Read the PDF file.
                                The generated voltage gets ADDED to the battery voltage in the ESC.
                                I did read the PDF file and its very confusing. Their attempt in broken english to describe the method leaves the content still suspect by my understanding of electronics. I see nothing that definatively proves the voltage can be above the generator effect of the motor or the stored value in the batteries. And to assume the volatge is additive? That doesnt make sense. During the braking effect current use is going to be the highest. Not the lowest. That means a voltage depression, so lower, not higher voltage values. Thats Ohms law. Current drain goes up and the inverse occurs to voltage. Not a surgence. Thats the first glaring issue.

                                The biggest issue with a prop turning and putting back voltage in the ESC with no braking is the FET's are turned off! Let go of the trigger and there is no longer any driver voltage to provide the so called path of conduction. They only open when voltage is applied. Let go of the trigger and guess what? No voltage, no path. Its pretty simple.

                                And lastly the most glaring error using the logic of additive voltage thru an ESC is the fact that there are many, and I mean many of us FE boaters that have data loggers were we monitor pack voltage. I have never heard of anyone reporting back that they saw a huge spike, certainly above their battery voltage. I have been using a Eagle Tree now for 3 years and not once. Not a single time have my plots displayed a voltage above my original starting pack voltage.

                                Like I said. I dont need myth busters for this one. Until I see a reproduction of the "effect" from one of us who shows how this can happen its dead in my opinion.

                                John
                                Change is the one Constant

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