Need help with center tap Xformer

[Chris Smith]

Must be on some other planet than earth? <p>Im afraid before YOUR theory of relativity of how the electron works,... gets published, you must work on dismissing two FACTS. <p>You must work on erasing the word “Alternating” from the statement “Alternating Current” with out any one objecting in the physics community, and two, you must some how dismiss the right hand rule for Electro Motive Force as being just bunk? <p>If you can pull this off, you can replace the conventional theories with your own. Good Luck.

[rshayes]

Here on Earth, the continuous random motions of electrons is an observable fact. It is called "Johnson Noise" or "Thermal Noise" and has a value of about 1 nanovolt per root hertz in a 60 ohm resistor at room temperature. This effect was identified about seventy years ago. It is a basic limitation on the performance of a considerable amount of electronic equipment such as TV sets and radar receivers.<p>Also here on Earth, several thousand physicists have spent about eighty years building more powerful particle accellerators. Not one of these physicists has accellerated a single electron to the speed of light in a vacuum. They keep getting closer, but they are not there yet.<p>There is nothing paticularly significant about the "right hand rule". If you are using conventional current it becomes the left hand rule. It would also have been the left hand rule if Physics had been developed in the Southern Hemisphere rather than in Europe. A physicist would use the "vector cross product" by the way.<p>Obviously your spacecraft's navigational system has malfunctioned and landed you on the wrong planet.

[Bernius1]

OK At the risk of sounding very,very,very redundant; If you take a center-tapped x-fmr, and use TWO bridge rec's, top & bottom with a 78L05 & a 79L05, you've got a nice bi-polar supply. NOW, take those two stacked bridge rec's on a 2-wire secondary (no center tap, or just disconnect it). Without the center tap, there's no fixed voltage division. Is there any advantage to having this type of floating ground ? AND, if the center tap is switched by a PIC thru a MOSFET, can you build a fully variable, computer controlled supply ?????
Have you heard of it being done, but not working well?

[rshayes]

Be careful how you stack those bridge rectifiers. If you draw out all eight diodes in the two bridges it is possible to have coonecctions with a diode or two in series across a transformer secondary winding. This will effectively short circuit the winding and release "magic smoke" from either the transformer, the diode, or both (most likely).<p>The use of a bridge rectifier with a center tapped winding is a fairly conventional way of getting positive and negative supplies of equal voltage, It is really just two full wave rectifiers of opposite polarity sharing the same windings.<p>Another variation uses a bridge rectifier with a center tapped winding to get two positive voltages. The negative output of the bridge is grounded, the positive output delivers the full secondary voltage, and the center tap delivers half the full output voltage. This was used in a number of amateur transmitter designs in the 1950's and 1960's. Replacement transformers for television sets were fairly easy to get. These usually had a 600 VCT winding, which gave 300 volts with a full wave rectifier. A bridge rectifier would give 600 volts, which was about what medium power tubes such as the 807 and 6146 operated on. The center tap supplied 300 volts, which was about the right value for the screen supply and low level transmitter stages.<p>Another unusual connection uses two center tapped secondaries and two rectifiers. The bottom winding has its center tap grounded. The center tap of the upper winding is used as the output. The two rectifiers are connected between the corresponding ends of the windings. In effect, this is the same as full wave rectifying the two windings, and connecting them in series, but only two rectifiers are needed instead of four. Additional full wave rectifiers could be connected to either winding to get other voltages (up to 4 or 5 different values). This could get pretty strange if the windings have different voltage and current ratings.

[Chris Smith]

And it has nothing to do with Electro Motive force. <p>Physics has not changed that much since I learned it in the 70s, and EMF stands just as it did back then, When you apply a Force on the electron, it moves in a orderly fashion, acording the direction of that force. <p>That why AC, has not changed, and thats why its still called AC.

Theories of the electron sitting quietly asleep in a conductor, VS current under pressure, share no similarity any more than Kirchoff’s laws which are algebraic expressions of how to count the beans moving, and they also don’t apply to the physical properties of the electron under force. <p>AC, stands at the end of all your attempts to say it doesn’t alternate,... for a good reason. It alternates direction with each half cycle.<p>Confusing the random Orbital spin of the electron with current flow down a conductor when a pressure has been applied, is your mistake.

And the electron at the speed of light, give or take a few feet, has already been discussed.<p>[ March 18, 2005: Message edited by: Chris Smith ]</p>

[rshayes]

Hello Chris,<p>Physics has not changed that much since the 1970's. I agree. However, the physics that you apparently learned in the 1970's was incorrect then, and is still incorrect.<p>The following is a direct quote from a physics text writen in 1960. Many colleges adopted this text for freshman level physics courses. For all I know, it may still be in use.<p>"In a metal the valence electrons are not attached to individual atoms but are free to move about within the lattice and are called conduction electrons. In copper there is one such electron per atom, the other 28 remaining bound to the copper nuclei to form ionic cores.<p>The speed distribution of conduction electrons can be described correctly only in terms of quantum physics. For our purposes, however, it suffices to consider only a suitably defined average speed V; for copper V=1.6 x 10^8 cm/sec. In the absence of an electric field, the directions in which the electrons move are completely random, like those of the molecules of a gas confined to a container. The electrons collide constantly with the ionic cores of the conductor, that is, they interreact with the lattice, often suffering sudden changes in speed and direction. These collisions remind us of the collisions of gas molecules confined to a container. As in the case of molecular collisions, we can describe electron-lattice collisions by a mean free path L, where L is the average distance that an electron travels between collisions."<p>"When an electric field is applied to a metal, the electrons modify their random motion in such a way that they drift slowly, in the opposite direction to that of the field, with an average drift speed Vd. This drift speed is much less than the average speed V mentioned above."<p>Halliday, David and Resnick, Robert, "Physics for Students of Science and Engineering (Combined Edition)", John Wiley and Sons, New York, 1962, page 689.<p>The drift speed is later indicated to be on the order of V x 10^-10, or about 1.6 x 10^-2 cm/sec.<p>Speed of light, c =3 x 10^5 Km/sec = 3 x 10^10 cm/sec
Average speed, V = 1.6 x 10^8 cm/sec
Drift speed, Vd = 1.6 x 10^-2 cm/sec<p>A previous example (on page 680) calculated the drift speed as 3.6 x 10^-2 cm/sec for a current density of 480 amp/cm^2 in copper.<p>In 1/120 of a second, the total drift would be 3 x 10^-6 meter. This is about 5 wavelengths of light.<p>Incidently, Kirkoff's Laws are not a result of bean counting or algebra. The voltage law is a direct result of the conservation of energy and the current law is a direct result of the conservation of charge. These are still basic physical laws.

[Chris Smith]

That’s the same physics that I learned which is why AC, two words describe it all.<p> The orbital spin and migration are for the purposes of studying the atom in space and time, not for Work done by the ampere. <p>The energy [electron migration] transmitted down a conductor still remains the same. <p>When a force is applies, they migrate one way, when it is reversed or removed, they migrate the other way, Hence the age old name, Alternating Current. <p>DC is merely one half of this force, hence it can be claimed that the electrons migrate in a one way fashion. <p>AC however, has two force vectors, thus the name alternating applies. <p>You can not have two vectors of force, opposite to each other, and have a energy flow remaining in only one direction. [work]<p> AC does not Ramp up, and then simply stop. DC in a Generator does this through the use of a commutator.

To best describe the electromotive force, and the current flow, a clothes line with two pulleys best describe the motions. First you pull the line a little, than you push it a little. The distance traveled for a given spot over one cycle is Zero, but the line or force, or electron, or amperage, did move in one direction, then it alternated back. <p>The orbital or random spin merely places the electron at a starting point, a reference in space and time. To consider work done, the electron must move some where down a conductor from its original place in space and time, and if it’s a single electron migrating from point A to point B or if you consider the billiard ball effect of one electron moving the electron next to it, and the one after that,.... really plays no role in the model of work, or the ampere, or current, because individual electrons acting on their own, or mass bumping, either way, electrons were involved [in work and migration] and moved down a conductor forming work or force [ampere] as they migrate in one direction for DC, and two seperate[half] directions for AC as it ALTERNATES directions, force, vectors of work, coulombs, and currents with each half cycle. <p>As per original misstatement made by others, Electricity does not go in a circle, one way unless its DC. AC travels both directions, once each way for one half one cycle.

In my class, “A hose full of ball bearings” was the terminology used to get most of the students to pass their test when they could not conceptualize the electron, and work. <p>Their random placement and individual movements inside the hose plays no role to the work, force, or ampere trying to be viewed <p>What is significant is that they are trapped in the conductor or hose, and only have two [usefull]directions that they can move in the real world, [excluding the atomic world and spin] and with DC its one direction, with AC its both directions, once with each half cycle. <p>You should never mistake the orbital path ways of the electron, with the general directions of electrons at WORK. <p>One is a individual description of a single item, the other is combined mass at Work, a average of many electrons pulling together to form Work. <p>Their actual position in the conductor plays no role, so long as the mass of the electrons involved moves one way to form work [DC], and then back in the opposite direction to form Alternating current, or work [AC].

[Bernius1]

3rd logical option; BOTH are right. Electrons move (Feynman again) about 1"/sec in copper wire. That seems to agree with Stephen. However, in AC, they'll move a little one way, and then back the other way. Remember , an amp is one coulomb/sec. So, at 60Hz and 1A, 1/120th of a coulomb moves a fraction of an inch each half phase, and then starts back in the reverse direction. This apparent movement is the SUMMED AVERAGE of all the electrons moving in pseudo-random fashion. Just like signal through a capacitor. No DC current flow occurs, but an average current does exist.
It seems to me that both of your points are valid, so there's no absolute exclusion of the differing opinion. Sigma. 'The sum of.....', always within a range and domain.

[Chris Smith]

That is why the word alternating has applied still to this day. Two force vectors must produce two angles of movment. Hence the words AC. <p>Also by the fact that both leads in a transformer, are hot.<p>The wire telegraph of the old west and transatlantic, and its speed [of work by the electron] down a wire, also speak for them self. <p>The Actions of the electron in a conductor, translate down a wire at the speed of light, give or take a few feet per second. <p>Tracing a single electron down a conductor is not the point, because the amp is work and it consists of many electrons in action, and work at the end of the day is the value or formulae that we count including the timing. <p>And work, or the actions of the many electrons still translates into roughly the speed of light in a copper conductor.<p>[ March 21, 2005: Message edited by: Chris Smith ]</p>

[Bernius1]

Like dominoes. Each moves slightly, but the initial tipping force carries indefinitely.

[rshayes]

There is no evidence for electrons moving at or near the speed of light. There is a lot of evidence against it.<p>Accellerating an electron to about half the speed of light takes a little less that 100 kilovolts. I can make current flow in a conductor by applying a few microvolts potential difference between the ends. This is obviously not enough potential to accellerate an electron to the 100 kilovolt energy level.<p>The energy needed to free an electron from the surface of a metal is in the range of 1 to 5 electron-volts. This was fairly well known by the 1930's since it affected the selection of cathode materials for vacuum tubes. A 100 Kev electron would be able to easily escape the surface of the conductor.<p>Ionizing an atom takes something in the range of 10 to 100 volts, depending on the type of atom involved. A 100 Kev electron that escaped from a conductor would generate several thousand ions in air before it came to rest.<p>A 100 Kev electron will cause the emission of moderately hard X-Rays if it hits a metal target.<p>So if I connect a 2 volt battery to a 2 ohm load, 1 amp will flow. The escaping electrons should ionize the air around the conductor, so I should see a blue glow, and probably be sun-burned by ultraviolet radiation emitted by recombining ions. I will also be exposed to a substantial dose of X-Rays.<p>Somehow, this doesn't happen.<p>Lead bricks are common items around particle accellerators. They are used to protect the personnel from stray radiation generated when particles travelling near the speed of light hit something else. These particle beams are in the microamp range. Yet we don't put lead bricks around computer power supplies where the currents are in the ampere range. Maybe its because there aren't any relativistic electrons running around loose. There is, of course, the CRT, with a 30 Kev beam, but we put lead in the glass of the CRT to absorb that radiation.<p>Electromagnetic fields do propagate with the speed of light. That is a demonstratable fact. It is likely that the electron motion in a conductor is a result of a change in an electric field rather than the cause. Such fields can transfer energy at very high rates. Radar systems can transmit megawatts through a waveguide without the use of a conductor at all. There is also a form of single conductor transmission line (Goubau Line or G-Line) that conducts energy outside the line. Both waveguide and G-Line are considerably more efficient that normal transmission lines in cases where they can be used.

[Chris Smith]

Dislodging the electron from the total orbit of a atom,[stripping] not hopping from atom to atom, takes many volts to accomplish and usually when this happens it either converts its excess energy into a photon, or simply ionizes the surrounding medium. <p>The reason is it takes excess energy to accomplish, is all energy wants to find a balance. <p>Most large Radar wave guides indeed do have a conductor, its called Freon. <p>Other than that, any concentrated beam of electromagnetic waves, radio waves, light waves can travel in free space the same as in a contained one such as the wave guide with out that much loss

[Bernius1]

ELECTRON-VOLTS. Correct. Distance matters ( Spark plug gap ), and charge builds at the tip. Take a spring-top 6V battery & a utility razor blade. Scuff the razor edge until arcing starts, then lift slightly off one of the pigtails about 1/64th inch (.4mm for the French ). The arc can be maintained until the steel vaporizes away. 6V, built up at the tip. 'electron-volts'. BTW, don't look at the arc, it'll burn your retinas (UV).

[bodgy]

And all this debate goes to show, is that in reality, science is nothing but mans interpretation of an observation.<p>And therefore can be challenged and altered at a later stage.<p>Now which of the 42 Brains (or is it 6?) are we living on today according to some Qantum theorists?<p>By the way pick up a copy of that august engineering journal Electronics and Wireless World (UK) and stand by for 6 months or more heated debates on Algabra (normally concerning Ivor Catt (Yup real name)), or how some damn fool <p>Colin<p>[ March 24, 2005: Message edited by: bodgy ]</p>

[Chris Smith]

Actually Bodge... <p>In between the semantics, smoke screens, and ignorance,...., the original concept of the post was does the energy of the electron flow in “one way”, for AC,.... when its called Alternating current? [silly ehh]<p> The fantasy that the energy force is not alternating over rode all the posts to create a massive misinformation post [s], like the barn yard noise when a fox is perceived but not really there,........ AS IF? <p>DC is said to go one way, yet the word “Alternating” was some how void of its actual meaning,......... for what reason?<p> ......So they can simplify a “equation” in their head, or just a false argument, ...or just plain ignorance?