Appling DC to a Transformer

If it is an ac transformer, the secondary will have a voltage spike at power up and then settle to 0v after a very short period of time. Since the primary is ussually a low resistance winding, you might draw significant current from the source aswell so be careful if you experiment with this.

The voltage impressed on the secondary winding will only be present as long as the magnetic flux level in the core is changing, i.e. while the voltage level in the primary is rising to that of the DC source. When the voltage level in the primary reaches the voltage level of the DC source, there is no longer any change in flux levels.

There is no such things as a transformer that is not an "AC" transformer.

Interesting... in my opinion this is the single biggest reason that AC distribution has become the world standard.

There is no such things as a transformer that is not an "AC" transformer.

Although I suppose one could argue that an ignition coil is a DC edge transformer?

Yes... I concede the point, however, the ignition coil still relies on a "changing flux level" and that requires some sort of "alternating" input voltage level.

Do you agree?

No. There's no such thing as a DC transformer.

The contact spike at the the (old...) ignition systems still constitutes an AC voltage.

The coil doesn't not react to the DC portion of the applied voltage.

To answer the post, what will happen depends a lot on which kind of smells you like.

Wangito.

Consider digital signals in which one (+) voltage is "yes" and another (+) voltage is "no." Alternate quickly between yes and no, and you still have two discrete DC voltages, one after the other, right? Do 60 calculations per second, (true followed by false followed by true...) and hook the output to a transformer. DC in... and the transformer "works".

I suppose yet another answer to the question of what happens to a transformer when you apply DC is that is acts just like the large inductor it is, and inductors are found all the time in DC circuits. (The secondary, just sits there, along for the ride, most of the time.)

See also my post 11.

I'm fond of that hot phenolic resin smell -- the one just before the smoke. The smoke itself is a little too pungent, unless served with a really robust cheese, like Stilton.

Ken if you keep going this way you are going to have to tell us what you mean by "is".

And soon, I'll be redefining "sex"

We had a thread, "What is 'Time'" with 166 responses. And I'll admit to having started a thread re "The Mathematical Value of 'of'" We can't be to far from the "What is 'is'" thread!

Agreed...

Continuing the conversation...

You would need more then 60 calculations per second to get a 60 Hz output at the transfomer. At an absolute minimum, you would need at least 240 calculations per second. As in...

Source 1 on, source 1 off, source 2 on and source 2 off.

Rick

True, we would need 240 cps.

Dear Ken

Transformer is basically a general term and in electrical electronics we now have a picture of it in one way. DC Transformers are not far away now but they do not resemple the core and transformer turns type transformers. If I say more I am bound to confuse more, those are already confused. So will not talk about this unless asked for.

Ignition coils are actually auto-transformers and even though power is applied to them is a DC voltage they are switched and impulse current flows that is used to generate changing magnetic flux.

DC-DC converters are excellent idea for those who think DC voltage can be increased or decreased by these devices without much loss of power. These use oscillator in between. Transformer core size changes with frequency. Small frequency means bigger core.

tpv = pow(10, 8) / (4.44 * bmax * secarea * freq);

Definitely agree re changing flux level. And of course, I also agree with the intent of your original post: Transformers are, certainly, generally considered AC devices.

So I am shaving a point pretty fine, here... not in the sense of "correcting" anything you've said so much as to promote outside the box thinking... and partly, of course, just to hear myself talk (read myself write?). And partly to get the original poster to really "think" about transformers, rather than to simply accept what any of us says.

So consider this: We all agree that the output of a PWM circuit is pulsed DC, true? Suppose, then, that we put an inductor and a capacitor across the output. The corners of the wave would round off and start to look like an approximation of a sine wave, but 0 volts would still be at the trough of the wave. Still DC? So then we add a transformer to the output, and look at the secondary voltage. The transformer would work just as you would expect it to with an AC input, but it is "really" a pulsed DC input. When read with an AC voltmeter, the transformer output would certainly seem to be AC, and you'd assume the 0 voltage level to be halfway up the waveform.

So, I think that strictly speaking, alternating current really has to "alternate," i.e reverse polarity with every cycle. Pulsed DC doesn't do that. But it can cause a transformer to operate. So a semantic twit such as myself would say, to the question "How would a transformer work on DC?"... "Just fine."

Yet another way to answer the question: much of what we "call" DC has an AC component: no power supply is perfect. So, if you hooked up a step up transformer to a DC source, it's output would be a multiple of the ripple voltage: step it up enough and a voltmeter would tell you that is is just like the 120 VAC found at a (US) wall socket.

(I should try this with a typical wall wart. It would make a fun science fair experiment for a mischievous kid: "Student proves that transformer can be used to change DC back into AC." )

Well said...

<OUTSIDE THE BOX>

I think that we are hung up on the "alternating" versus "direct" parts.

Let's face it... all we really have is current. As soon as we do anything in any way to change, vary, interrupt, or whatever term you wish to use, to the level of a current it becomes an "AC" current, at least it does IMHO.

If we establish a current and do not change it in any way, it is a "DC" current, again IMHO.

</OUTSIDE THE BOX>

And yes I agree... that would be a good school science project. Better then the hydrogen explosive device me and the daughter built when she was in junior high school.

Rick

Actually the voltage is induced in the secondary only while the current is changing in the primary. The applied voltage appears instantly across the primary. The current in an inductor lags the voltage (by 90 degrees). The amount of time the current will rise may be calculated by T=1/RL, the inverse of the capacitive time constant.

Nothing useful unless smoke and heat is what you intend. Transformers work on ac because it is the change of direction that causes the change in flux that couples the voltage current into the secondary winding. The turns ratio determines the the out put voltage in relation to the primary voltage. In the UK we have 240V ac mains and the primary turns is usually about 4 to 6 turns per volt and the secondary is then calculated to allow for the current/power out required. This requires to know the application and location, the wire gauge determines the current, the core size and shape, are also important, it can be made up of "E" "I" laminations or a toroid dough nut, for more specialist applications "C" cores are used. Switch mode supplies use powdered iron because of the high frequencies used would just wast too much power heating the core. Saturation is when the flux in the core reaches a maximum and the core can no longer cope the result is loss of voltage and lots of heat. There are isolated windings where two bobbins are used or the primary winding is covered with plenty of insulation the the secondary is wound over the top "Toroid". Then there are the non isolated types "Auto transformers where there is only one winding and the voltage is tapped off using a moving contact, these provide a means to control the voltage but do not isolate any thing. There are center tapped for split rail supplies and tapped primary types for varying input voltages. 120 0 120 or 220 230 240 V ac in. The variety is endless. But no DC.

It will heat up like a heater.

It is as goos as connecting the transformer to a bettery. Following could be the outcomes:-

1) The voltage will continuously increase till it reaches the DC voltage. Curent will come to Zero from initial high current.Since the secondary circuit is not colsed and not able to draw current, energy has to be dissipated some where.

2) There are two aspects of it. One is flux need to be balanced and it can not be done since the secondary circuit is open. Most of the current has to pass through the insulations and other accessroies. IT WILL HEAT UP THE SYSTEM.

3) It is similar to short circuit in primary winding -

4) Core will get damaged as it has to take all the load and system get heated.

Not correct.

DC current to transformer never comes down to zero unless DC resistance of the coil is infinity. Output will be zero voltage and zero current.

DC resistance of the primary coil will heat the transformer and the current will continue to flow through primary coil DC resistance.

Even rectified DC voltage not fully DC will also heat up the transformer input coil.

Surely the DC current into the transformer will come down to zero shortly after the smell begins? Once all the smoke clears you'll find the input current is zero. This does depend on the relative specifications of the transformer and the DC current source but is a possible outcome.

RF coils used to block AC are good example of it. They allow DC current to flow and try to block the AC due to jwL greater impedance formation. Frequency going to zero means ZL going to zero with some normal resistance of the coil not being a supper conductor will let all the current flow through using simple ohms law. I see a lot of smoke in this simple question. I do not know why? You point is right that when one connects the power, at that time it is never DC.

What are you smoking?

I will try to summarize the various responses:

1. Applying a DC voltage to a primary or secondary of a transformer will result in a current flowing through the transformer windings. This current will obey Ohm's law, meaning that current flowing will be proportional to the voltage and the conductor DC resistance. Actually nothing will happened except heating of the transformer as long as the current carrying capability of the conductor are not exceeded. If they are exceeded, than overheating of the transformer will probably result in the destruction of the transformer if not stopped.
2. Conclusion: No transformation of voltages will take place.
3. In order to cause transformation of voltages, an AC voltage must be applied to the transformer windings. The alternating current will cause changes in the magnetics flux, or more simple, in the magnetic field of both windings of the transformer, and a transformation of voltages between primary and secondary windings will take place. This is what a transformer is all about.
4. Hope this answers your question in full.

Wangito

The current will not act like an ordinary DC current since our old friend inductance acts like a resistance and it takes some time constance to reach maximum current. Then depending on the number of turns and size of wire - the current might overheat the windings - then maybe not, if it is a step-down transformer, the current might be pretty low. it also depends on which side of the transformer you connect the DC voltage. It also depends on how much DC voltage you have.

A DC current thru a Winding will produce a pulse in secondry & settle down to V/R of the winding. If the voltage applied is sufficient to draw heavy current it will damage / burn th transformer. As there is no Impedance of transformer to DC current [due to no-back EMF or Inductance is not offering any reactance on DC current] XL= 2 x Pie x f x L where f is zero so XL= 0. The current is only limited by the Resistance of the winding to which DC V is applied.

Transformers are generally engineered and fabricated to use on AC. To compensate for the necessary inductance the DC resistance is very low. Unless the voltage is very low, applying DC across a transformer will accomplish what we call "letting the smoke out", as what has been alluded to in other responses.

Use of DC current in HV side of a power transformer is frequently used in order to measure the HV, DC resistance of the winding. This must be carefully made with a test source.

If you are using a current transformer, you may harm it if you inject the current in the primary(low current) side, as you will have a transient that will cause a momentary induced overvoltage that can produce a extremely high voltage in the secondary.

The effect is particularly important when this CT is used for protection, as you will polarize the CT and you will change the saturation conditions thus preventing correct protection operation.

on old submarines where DC is the only type of power

the way it is done is by motor driven generators a 440VDc motor drives a 220VDc generator, or the main batery is rearanged via Mid point link switches switches to make the 220v dc, read an old electrical manual for a british/canadian Oberon "O" class sub.

and what was done for 330V and 110V splitting?

I don't think ever 440V DC batteries were made in one casing. Those must be some 12V in multiples. It is easy to take out any DC voltage in multiples of 12V DC.

Power oscillators and transformers were known for long from the time of Faraday.

Were those ships very old from the time of Columbus and Vascodagama?

What is that "O" Class Sub? Can you educate me on that?

The USN submarine battery is made up of many one cell batteries connected in series-parallel to provide 250 VDC at the output. Each cell is huge; six feet high or so. The old subs used lead acid but the nukes use a newer technology. We are not talking car batteries.

I have seen one American SUB at San francisco in which Torpedo (may not be real) were there but no real batteries were seen. Good that you told me that they are so big. I have seen at best truck batteries and some under the train car in AC coaches. Were you on some nuke sub? I have seen those in fiction movie only. India now have some dirty Russian nuke sub. I will not like to go near them for sure. I am also scared to be under water for months in that small casing. I like lots of free space and big rooms, high roof etc.

Does anyone remember when car radios had vibrators that drove a transformer to get the high voltages needed for some of the tubes. The vibrator chopped the DC (6 volts or 12) and the output was 2 or 3 hundred volts.

The model A Ford had an vibrator that put out a constant AC voltage that was switched via the distributor - an other DC transformer?

A switched DC source, such as you mention (and I do remember the units your are referring to), becomes in essence an AC source, does it not?

These old vibrator power supplies were probably the inspiration for today's switched power supplies. In switched power supplies, typically the input is first rectified from line voltage. Then this is pulse width modulated into (by definition) pulsed DC. These pulses are then fed though a transformer (usually at much higher frequency than line frequency) and rectified yet again.

So is pulsed DC really AC? In one obvious way it is not -- at least, it is of a different character than the usual AC: it's idealized wave is square, and AC's idealized wave is sine. Also, ground voltage is typically at the crossover point in AC current and at the base of the waveform in pulsed DC. Thirdly, the output waveform of a transformer hooked to AC will look very very similar to the input: a nice smooth sine wave. The output waveform of a transformer hooked to pulsed DC will usually not be a square wave, but instead a series of spikes and resonances. Fourthly, the pulsed DC current that flows though mechanically commutated DC motors is again different in waveform from typical AC -- and you'd have a hard time convincing most plant electricians that the current flowing through a DC motor is AC. Lastly, the conventions we use to name voltages are quite different: 120 VAC is an RMS voltage. (.707 times peak) (Peak to peak would be even higher, at 338 V.) 120 VDC pulsed is just that: 120 V peak to peak.

So, here's yet another in this long line of answers to the original question. If you want to see what happens when you connect DC to a transformer, just look inside your computer's power supply.

The first posted answer is very good really: You see a pulse from the secondary when you connect DC, and another pulse when you disconnect. (Whether you also release some of the magic smoke after the connect and before the disconnect is dependent on the transformer and the power available -- but an old ignition coil is a perfectly good transformer and can be left connected continuously -- ignition on, engine not running -- all day long, eventually reaching equilibrium at a temperature not too hot to touch.)

I believe they were called multivibrators, but that was a long time ago and my memory is gone.

Hello imart23

What is that "imart23" in any way? Is it that "I am smart 23 times than you". Not a bad idea. Good.

I have seen one gas lighter that operated with such voltage switcher which generated fifteen thousand volts in a small package. I then purchased few those autotransformer coils that have several separate windings for about 2.5kV each segmented in 7 zones to avoid spark over.

There were also pencil HV vibrators used for muscle tone treatment to give mild shock. Then finally you may know that heart defibrillator which jump start the heart once back to normal when it get stuck for various reasons. These for remote areas use DC battery and high voltage impulse generators.

Yes, I remember them well! Interesting how memories like can seem virtually lost -- I haven't thought of them in many many years -- but now that you mention it, I remember them clearly. Car and table top radios use to have to "warm up" before you really use them -- almost as bad as having to wait for your computer to boot up, but not quite!

Here is probably the definitive test for AC.

If

Then it's not DC and therefore must be AC

It certainly works 100% when dealing with transformers.

There seems to be a considerable amount of confusion over how a transformer actually works. It's a long time since I studied transformer theory so I will not go into it myself, but, Tony Kuphaldt has a good page on transformer theory that explains it well. I suggest following the link and reading what he has to say.

If anybody would like any further explanation pleas don't hesitate to ask and I will try and help.

Personally, I think that definition is far too broad. If you enter "define alternating current" into google, you come up with this list of definitions, virtually every one of which speaks of reversal of current direction. For example:

An alternating current is one whose amplitude of current flow periodically rises from zero to a maximum in one direction, decreases to zero, changes its direction, rises to a maximum in the opposite direction, and decreases to zero again.

A simple change of voltage with time does not necessarily imply a change in direction of current. Strictly speaking, your definitive test for AC means that DC does not exist: I have never seen a "DC" circuit in which voltage does not change with time. In some, this change is slow, as in the discharging of the supply battery, in others, it is a bit faster (as in the change in voltage with every change in load that occurs in every real world circuit), in others it is faster yet (such as in any power supply, all of which retain some ripple) and in yet others, very fast (as in the change in voltages in digital circuits).

Thus, PWM circuits are a form of DC circuit: they are supplied with DC, they feed DC sinks (DC motors or example), and all the components in them are essentially DC components. But the waveform wouldn't come close to passing your test for DC. Pulsed DC is not AC. All that is required for a measurable change in voltage or current at the secondary of a transformer is any change in the magnetic field at the primary: on/off transitions, DC pulse trains, AC.

I agree with you ken as electrons never move in a group unless we are talking about supper conductors. While electric or magnetic field makes then to drift in one direction, they do have multiple reversal before they can do that and under go mean free path collisions many times. In some material drift velocities are high and charge carriers can move without recombination or collisions. If you think the conductor free of atoms in between and like vacuum tube influenced by field then electrons experience external field and their own. In crystals they also see nucleus other than electron clouds. An average picture is a much better idea to get to the electron behaviour in metals. Not all free electrons are quantized with same energy level and then you need to consider the interactions among then when you increase the field and the kinetic energy of the electrons is affected.

In oscillator field the behaviour at low frequencies is almost to what you call DC and I agree that there is no real DC. When there is no current that does not mean electrons are at rest. There average motion is almost at zero current such that you will not see any magnetic field outside.

"A simple change of voltage with time does not necessarily imply a change in direction of current. Strictly speaking, your definitive test for AC means that DC does not exist"

Not by itself, however, you can describe any voltage as a combination of a pure DC voltage with any combination of AC waveforms.

Dear thirumalai

in transformer

for varying flux there is an induced emf in secondary as well as in primary also

this primary induced voltage opposes to the main applied voltage so that net voltage acting on primary is not significant to cause large current to burn the primary winding

but in case of dc

there is no induced emf as it is constant w.r.t. time

so voltage applied to the primary is severe & causes heavy current in primary

this may cause to burn the primary winding & there after other parts also if protection system doesn't come into function

feel free to ask more if needed.

When a transformer is connected to a DC supply

1. The primary winding just acts a resistor connected to +ve and -ve terminal of the DC source

2. The resistor resists the flow of current and disipates the power in for of heat

3. if the winding is having very small cross section and low resistivity then it will melt or bow off due to enormous current flow through it

4. transformers output is purely dependent on the electro magnetic induction. since DC no frequency and no flux linkage with secondary hence no emf is produced in Secondary

Thalib..

I'd agree with virtually all of this, except the first line: Instead of "when a transformer is connected" I might say "after a transformer has been connected". At the instant when a transformer is connected to a DC source, there is a spike and resonances generated in the secondary, and reflections in the primary. Similar things happen at the instant of disconnection: the rapidly collapsing field in a conventional ignition coil (when the points open) causes thousands of volts to be produced at the secondary.

Unlike Masu, I would consider an ignition coil a DC device, with its output related to a DC edge or transition. Alternating current reverses in polarity; it does not simply change in voltage. (For example a step from +5V to +1V would cause a collapse in the magnetic field in a primary winding, and that change in flux would cause an output at the secondary.)

For me, (and, I believe, for most people who work with electricity) pulsed DC is not alternating current because there is no reversal in polarity, an essential part of the alternating current definition. A pulse train fed to a transformer causes a response from the secondary: a transformer, to transform, requires only a change in flux, not a reversal.

Along the same lines, I'd consider the output of a half wave rectifier to be pulsed DC (as it is shown schematically) This pulsed DC can be fed into a transformer, and the transformer will have a predictable output: also pulsed DC: bigger or smaller half waves.

AC must reverse polarity to be AC. (If that were not the case, it could simply be called VC for varying current.) DC can be pulsed without reversing polarity and is not, by definition, AC. Pulsed DC can "operate" a transformer in a manner beyond simply heating up the primary coils.

your are correct Blink. once i tried to connect the 12V, 7.5AH battery at primary and got a heavy sock when i touched the secondary.. at that time i was trying to design a inverter for 12- 230V . unfortunately the firing circuits didn't work well.

Seems like there has been quite a bit of arguing back and forth here about what is what. The original question only asked what would happen if DC were applied to a transformer.

As some have directly answered that question, yes, when DC is first applied to the primary winding, a pulse happens, which then shows up in the secondary winding due to the change in flux. If the DC remains connected, depending on the amperage applied, varying amounts of heat will be generated, which may or may not end up in smoking the transformer (depends on how much current is applied). When the DC is disconnected, the drop produces another pulse, which then shows up in the secondary.

Pulsed DC through the primary produce pulsed changes in flux in one direction, which show up in the secondary. DC does tend to have more loss due to heat because the current is only going one direction, therefore it has to go the whole way through the circuit, enduring the resistance of the whole circuit, to make it back to the electrical supply.

AC means "Alternating Current". In this context, it means current which CHANGES DIRECTION or polarity. The whole reason they came up with the idea of AC was to make the electrons travel only half the distance in the circuit, thereby only having half of the resistance of the circuit, and approximately half of the heat loss.

AC has its uses, and pulsed DC has its uses, but both produce a change in flux, which is the only condition needed for the transformer to convert electricity from the primary winding into a magnetic field in the transformer core, and then use the collapse of that magnetic field to cause electrons to flow through the secondary winding.

AC causes a dramatic change of flux. The initial electron flow charges the magnetic field in the core with one polarity. Then the drop to zero voltage, continuing reversal of electron flow, and resulting magnetic field polarity reversal with subsequent collapse of that field causes the transmission of electricity from the primary to the secondary windings using only half of the current requirements as pulsed DC would.

By alternately reversing the polarity in AC, the circuit receives twice the waveform amplitude that would occur if the same voltage of pulsed DC were used. This equals twice the ability to move electrons through transformers.

However, a stepped motor, or a pulsed electromagnet in which the application required the magnetic field polarity to remain constant would be two good examples of uses for pulsed DC current. Basically, pulsed DC is perfect for any applications which require both a constant polarity, and require the use of a transformer to increase or decrease the voltage.

"AC means "Alternating Current". In this context, it means current which CHANGES DIRECTION or polarity. The whole reason they came up with the idea of AC was to make the electrons travel only half the distance in the circuit, thereby only having half of the resistance of the circuit, and approximately half of the heat loss."

The big advantage that AC has over DC is that you can easily change the voltage using transformers. The upshot is that with AC you can use extremely high voltages at the transmission stage and then considerably lower voltages at the end users stage.

By doubling the voltage you halve the current and since the loss in the transmission lines is proportional to the square of the current you have reduced the line losses by a factor of 4. Step the transmission line voltages

So if you use a 110 V end stage voltage and 110,000 V transmission line voltage the line losses are reduced by a factor of 1,000,000 over that of a comparable DC system that need to use 110 V throughout.

How about magnetic amplifiers? This a transformer with an extra coil or a tap in one winding. DC is applied and by saturating the core is prevents the rise and fall of magnetism that follows the AC sine wave (or saw tooth, square wave). The amount of DC voltage is varied and gives control of the output of the transformer.

In the control winding, the resistance is higher than in the AC windings so the DC current does not need to be limited by inductance. MagAmps are engineered for this function, not like a transformer that doesn't like DC streaming through it.

I hooked up my circuit for the 555 timer circuit you detail elsewhere, but am having difficulty getting the circuit to produce anything but 5v 25kHz signals out the other side of the transformer. Does that circuit require a special type of transformer to convert the high frequency pulsed DC at 5v into a higher voltage output?

What is the step-up ratio of the transfomer you are using?

In rep TO:

Blink #36 In reply to #32 vibrator power supplies

&&&&&

Kyoto #33 In reply to #31 multivibrators

Reply:

They were called "Vibrator-Supplies". There were 2 types;

1) Non-Synchronous - Just not only making & breaking, but alternating DC current thru primary of a transformer, stepped-up in secondary; rectified by rectifier [Selenium-rectifier, the 1st generation of rectifier]; having 1 NMC [Normally made-contact to energise a coil & then keep it vibrating by opening/making this contact. The 2nd contact a CO [Change-over], atlernating thru primary.

& the

2nd Synchronous - had a 3rd CO contact working in Sync for keeping one end of Secondary always(+) & the other always (-).[Functioning as a commutator works in a DC Generator to keep one always (+) & the other end always (-)]

Multi-Vibrator is the Electronic Circuit While "Vibrators" used in vibrator power supplies was Electro-magnetic device.

&&&&&

Shyam #40 In reply to #39

Dear Sir you have mixed up Semi-conductors to Pure-Conductors like copper.

In Semiconductors there is "Storage" effect in Semi-conductor causing delay in reversing flow of current, but there is no such thing in Conductors & current instantly reverses.

It is only the Inductanse of Windings which delays the change in direction [Current rise/fall lags the rise/fall in voltage in a coil.]

&&&&&&&&&amp;&&

mohammadthalif #42

"4. transformers output is purely dependent on the electro magnetic induction. since DC no frequency and no flux linkage with secondary hence no emf is produced in Secondary"

Flux-Linkage is thru the Magnetic-Field & it is there due to I x t xby mue of Core.

My dear it not the Flux which induses [Produces] but it the change of flux. More change/sec

will produce more Voltage & less will produce low voltage. Flux-density has NO effect, but the Rate of Change of flux [df/dt]. Density of Flux plays its part in Power NOT in Voltage.

As it is clear from Maneto-Gas lighter in which a magnetic circuit is disturbed by a Revolver-like Triggered magnetic-material FIRED [so-fast as the revolver is]thru a magnetic-field of a small magnet, but induses a very hi-Voltage & causes an arc-over [spark]in an air-gap.

Mr. Shyam is well coversant with such devices.

&&&&&&&&

jmart23 #47 "magnetic amplifiers"

magnetic amplifiers are very special devices, used in Ships, have a very complicated theory.

Generally their some parts operate in "Saturation Mode", Signal coupled thru other connected Magnetic-circuits & the out-put is a magnified [or amplified] signal.

An-other example of Saturated core used is in Ferro-resonent Voltage-Stabilizers where a part of core is saturated by a Series-Tuned-Cct composed of winding around this core in series with a capacitor @ power-freq [50 or 60Hz]. Its theory is also not simple to describe here.

&&&&&&&&&amp;&&&&&

Guest #44

I agree fully with you & I had pioted it out that we should keep within the asked question.

Regards

&&&&&&&&&amp;&&&&

masu #45

There is no half-way in Electricity. It is always "Coplete-Circuit". All the heat & Power loss is full I x I x R.

Actually we forget the history of inventions. AC generator [called Dynamo in relation to Bikes]

was the 1st thing invented, while in motors it was a DC motor.

Butin Power domain Dc Generator was the leader of AC generator [Alternator] though its tech-know-how was well known. Reason not known?

Alternators took-over when long-distance Power-Distribution came in the play.

It was economical to rise Voltage high enough to reduce current & using small size of conductors. Economy in erection, maintenace & cost of material.

You Sir are correct - however the question asked what happens when DC is applied to an AC transformer. The answer depends on several things: what size transformer, what size are the windings, what is the dc voltage applied, is it a step-up/step-down transformer, what is the ratio, how robust is the dc supply?

45 years ago I shocked many of my schoolmates using a flashlight battery and a step-up transformer (or a step-down transformer used backwards). The 1.5 volt battery never burned up a transformer.

So the answer depends on a little more information.

I still have a old AM automobile radio that works off of six volts and uses a multivibrator to chop the dc voltage and feeding through a transformer with tube rectifier and then through multi resistors acting as voltage dividers to give the various voltages needed. When using a multivibrator the 0 voltage in effect becomes half way between 0 and 6 volts, the secondary is more like a saw wave. With the proper filtering it can approach an simulated sine wave.

The magnetic amp is like any other amplifiers it uses a small voltage to control a larger voltage. I (when I was about 12) read an article on liquid amplifiers and it made it clear to me how an amplifier works.

Please see my Post #51 which reads as follow: [xx] are added for clarification now

I hope that something is clarified in my early post. Regards

Re: transformer 03/26/2007 4:29 AM

[ A DC current thru a Winding will produce a pulse in secondry & settle down to [current]=V/R of the winding [to which DC is applied]. If the voltage applied is sufficient to draw heavy current it will damage / burn th transformer. As there is no Impedance of transformer to DC current [due to no-back EMF or Inductance is not offering any reactance on DC current] XL= 2 x Pie x f x L where f is zero so XL= 0. The current is only limited by the Resistance of the winding to which DC V is applied. ]"

Of course it is 1 pulse which actually had settled down to zero after a little time, but you felt that it remains for long time.

Had you done the same thing when disconnecting the cell, you will again get a Hi-voltage pulse & shock. I don't like to go in details, but simply:

1. A coil [like Windings of a transformer] STORES energy like CAPACITOR, but a difference is that COIL is Charged with CURREENT & discharges its energy as soon as current is changed [increased or decreased] to maitain the current to its original level, while a capacitor holds energy in form of voltage & opposes change in Voltage; ie it releses its stored energy if source voltage decreases due to increased load or fall of input voltage source; & absorbs if the sorce increases.

The coil will do the same thing for changes in current; it will produce revese-voltage if current is increased & in-phase-voltage if current decreases to maintain current constant.

But mind that this all functions till the energy in Coil & Capacitor can maintain.

Factually for very short-term changes [fluctuations or Ripples] & not for long-term such as Brown-outs or over-voltage.

Capacitor can hold energy for long time even after voltage source is disconnected, but Coil will release all its energy in form of Hi-voltage Pulse if the current source is disconnected. Which you feel as shock.

So the answer depends on a little more information.

"I still have a old AM automobile radio that works off of six volts and uses a multivibrator to chop the dc voltage and feeding through a transformer with tube rectifier and then through multi resistors acting as voltage dividers to give the various voltages needed. When using a multivibrator the 0 voltage in effect becomes half way between 0 and 6 volts, the secondary is more like a saw wave. With the proper filtering it can approach an simulated sine wave."

It is not "Multi_Vibrator" but Vibrator-Supply called in those days.

Its function I described briefly in my post above #51

The magnetic amp is like any other amplifiers it uses a small voltage to control a larger voltage. I (when I was about 12) read an article on liquid amplifiers and it made it clear to me how an amplifier works.

Fine if you have grasp of "magnetic amps" otherwise was not a common subject.