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  • #31
    I always wondered why rotax put that critter in there as cuyuna JLO, BSE and other engines with the Bosch energy transfer ignition system didn’t have it. I have run many hours without the box there without a problem.
    norm

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    • #32
      Here is what I believe now after much thought:
      Capacitor and coil form an oscillating circuit, therefore several alternate sparks, every time. Only the first spark is useful for gas ignition while the nexts just does produce unnecessary heat on the electrode.
      This possibly makes a soot point hot enough for self-ignition before the separation of the next round and severe loss of engine power (not to mention the severe mechanical overload of the elements)
      The ignition damper box prevents this.
      Last edited by Jean Claude; 04-11-2018, 02:53 AM.

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      • #33
        I think there’s more to it than that, JC.

        Battery ignition does not require a damper resistor because after points open, no more energy is being supplied to the ignition coil.

        With a flywheel magneto, rotating magnets continue supplying energy to the ignition coil after opening of points.

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        • #34
          Originally posted by phantom View Post
          I always wondered why rotax put that critter in there as cuyuna JLO, BSE and other engines with the Bosch energy transfer ignition system didn’t have it. I have run many hours without the box there without a problem.
          norm
          They use them on starter and coil switched main bus relays too.
          https://www.youtube.com/watch?v=bvDuyM2e4gw

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          • #35
            Rotax 503 works as well without a spark damping box, like all other engines with flywheel magneto.
            In my opinion, this box just is a cheap safety measure for use on aircraft.

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            • #36
              t’s a mystery, JC, because most of the energy stored in the ignition coil is dissipated in its own internal resistance when the spark plug fires. I doubt if the back swing is significant.

              It is different from turning off relays and solenoids.

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              • #37
                Chuck,
                In the case of the magnetic flywheel, the energy is stored in the internal coil. The external ignition coils are simply transformers. Their primary / secondary coupling is probably loose enough to allow a significant back swing, despite the first spark.
                Click image for larger version

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                • #38
                  Of course the amplitude of back-swing voltage depends upon the amount of “leakage” inductance. I don’t have a Rotax engine in front of me but my recollection is that the ignition transformer has a complete magnetic circuit without an air gap.

                  Before “Kettering” single spark ignition was invented, early spark ignition engines used a “shower of sparks.” Model T Fords used ignition coils with a built in “buzzer” that made continuous sparks as long as power was supplied.

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                  • #39
                    Well after seeing this topic discussed several times over the years in amazement !!
                    This damper is actually called a SNUBBER.
                    It's propose is to clamp FLYBACK caused from a collapsing inductor.
                    Since you have a stator and a transformer in series, the SNUBBER stops oscillations from occuring that may damage the points and keeps the coils from saturating after discharge.
                    The discharge and saturation rate will stay constant with the opening and closing of the points.
                    In other words ,it will only fire one time per saturation with less arc on the points.
                    All coils have a large flyback and that's what causes the high energy spark, but this also causes feedback in this ignition circuit.


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                    • #40
                      The condenser prevents arcing at the points; slows down the rate of voltage increase when the points open, giving time for the points to separate.

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                      • #41
                        Originally posted by C. Beaty View Post
                        Of course the amplitude of back-swing voltage depends upon the amount of “leakage” inductance. I don’t have a Rotax engine in front of me but my recollection is that the ignition transformer has a complete magnetic circuit without an air gap.
                        Chuck,
                        Without air gap, the magnetic flux in the iron does not return to 0 after the inductor current disappears, due to the résidual magnetization. So, Each new pulse of the same polarity will gives more quickely the saturation and will produce the flux variation outside the magnetic circuit. Hence the leakage inductance, even without air gap.
                        Last edited by Jean Claude; 04-12-2018, 06:21 AM.

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                        • #42
                          Originally posted by C. Beaty View Post
                          The condenser prevents arcing at the points; slows down the rate of voltage increase when the points open, giving time for the points to separate.
                          I agree with that, Chuck.
                          Last edited by Jean Claude; 04-12-2018, 06:02 AM.

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                          • #43
                            Originally posted by Jean Claude View Post
                            Chuck,
                            Without air gap, the magnetic flux in the iron does not return to 0 after the inductor current disappears, due to the résidual magnetization. So, Each new pulse of the same polarity will gives more quickely the saturation and will produce the flux variation outside the magnetic circuit. Hence the leakage inductance, even without air gap.
                            You’re right, JC, there has to be an air gap to prevent saturation of the transformer core.

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                            • #44
                              (Sorry for out of topic.Did not know how to send a private message to Chuck Beaty. Although the topic is kind of Engines.)
                              Hi,Chuck.
                              Merry X-mas and soon happy New Year! Hope everything is as good with you as possible.I was watching this video ( https://www.youtube.com/watch?v=AXddqiuDL2Q ) and in the post comments talk about power and torque. Immediately started thinking how millions years ago you were helping people on the Forum to understand this topic.
                              See you one day.Regards.Georgi.

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                              • #45
                                The circuit diagrams given(I'm assuming for Rotax engines) seem over complicated and 'ancient'. First of all, ignition coils, being Tesla coils, are among the first types of electronic transformers, which generally increase voltage, while decreasing amperage. Ignition coils have two coils each. The primary coil has thicker windings, with only 20 or 30 turns, and today usually runs at 12 volts(battery voltage). The secondary coil consists of much finer wire, but has hundreds of windings. This secondary coil usually runs at 15-25 thousand volts. The primary and secondary coils are not directly connected to each other.

                                For many years in the automotive world, the primary ign coil would be charged up at 12 volts by the car's battery, by the generator, or by the alternator. This charging would only take 5-10 thousandths of a second, depending on engine rpms. The car's distributor controlled this 'dwell' time as it rotated a lobed cam. The cam opened the points, thus briefly turning off the low-voltage current to the primary coil, and collapsing its electromagnetic field. The collapsing field then 'induced' a high-voltage current into the secondary ign coil, which fired the spark plug in the proper cylinder, a predetermined number of degrees before Top-dead-Center(also selected by the distributor lobes). A fairly large capacitor was connected to the primary coil circuit and to ground. In small 2-4 cylinder car engines, the capacitor was screwed to the outside of the distributor. In 6-8 cylinder engines, there was room for it inside the distributor, under the distributor cap. The capacitor was needed to prevent the 200 or so volts of primary back-voltage from oxidizing(burning up) the points prematurely in a couple hundred miles. Even with capacitors, the points would burned up in 6-12 thousand miles.
                                Regards

                                Frank

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