Body
OleThank you for the basic review, which is helpful to always keep in mind as we grapple with squeezing out a little more energy from devices.Keeping pictures in our minds helps to visualise and perhaps find new combinations.Cheers Warren
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On Tue, 21 Aug 2018 at 7:01 AM, [email protected] [EVGRAY]<[email protected]> wrote:
Hi Kone,
Look at it as energy instead of just voltage current and time. Electrical energy contains all of those three parameters. For the flyback pulse energy is first stored in an inductor (coil). When applying a voltage across the coil this starts the current. The charge carriers start moving faster and faster in an exponential way until only limited by the resistance of the circuit. This current represents a magnetic field formed through the coil and around all the current carrying wires and thus stores magnetic energy. When opening the circuit the magnetic field collapses from the value it has during opening the circuit. The collapse also keeps the current at the value it has at that same moment of opening the circuit as this current is what makes that size of magnetic field through the coil and the rest of the circuit. From the point of opening the circuit the magnetic field and the current begins declining in an inverse exponential way. I.e. the current drops very fast in the beginning and decreases at a slower and slower rate.
As the coil after opening the circuit has changed from a sink to a source by changing from absorbing energy to giving off energy it is now a generator (instead of a motor). The induced voltage given off by the coil is the rate of change of the current multiplied by the inductance of the coil. Mathematically it can be written as:
where v is the voltage i is the current t is time and L is the inductance of the coil. The t in parenthesis indicates the letter before the parenthesis is a function of t (time). The d before i and t indicates a differential change in those values. Greak letter delta can also be used for such a change. Source of the above formula: https://wiki2.org/en/Inductance.
As the current has a very fast rate of change [di(t)/dt] just after opening the circuit this means that the induced voltage or flyback voltage will be great at just that moment. This is known as the flyback voltage in the discipline of electronics. The faster the opening of the circuit the faster the energy is given off and as power is the rate of energy flow [P = dE(t)/dt] this also means higher power the faster the circuit is opened. E is here energy and P is power. What limits opening the circuit is capacitance which stores energy. For a fast decline in current (i.e. a fast rate of change in current) all capacitance must be minimized. This was what Tesla tried to do with the Tesla transformer. But even the vacuum of space has capacitance thus capacitance can't be totally avoided.
In most circuits the rate of change is limited on purpose by using snubbers to prevent the voltage from punching through the insulation.
For a capacitor discharge just switch around voltage and current in the formulas as well as switching C for L (switching capacitance for inductance).
Source: https://wiki2.org/en/Capacitance
C is the capacitance while the rest of the letters are as for the first formula.
Regards
Ole
---In [email protected], <konehead@...> wrote :
Hi Ole
The sink or source power quadrants I look at as sort of flat scale but with flyback it happens at border line between sink and source perhaps you could say, and it shoots out "sideways" either at you or away from you, and in my brain it shoots both at you and away from you at same time "flash" too for near twice the speed of light (perhaps you could say)
So I think Mick and I are asking the same question (sort of) and what would be the analogy of the flyback spike in coil to whatever the opposite would be.in a capacitor.
All I can think of is the immediate inherent back emf force in electrical flow that resists the movement....but perhaps upon discharge of cap there is something else not looked at so much since it stays within the walls of the capacitor does not do damage like flyback spike....(I don't know just thinking)
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