DC through a step up transformer

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No, a transformer is (most of the time) used to convert from one ac voltage to another. An inverter is the device that converts dc to ac. A transformer does not work with DC, unless you "trick it" by turning the dc current on and off - but then you dont really have dc anymore.....
 
Surprising to many, the answer is yes, and in fact was once pretty common.

What people would do is take a common relay and put its nc contact in series with its own coil.

A n/o contact would feed DC into the primary of an xfmr.

The relay would happily chatter on and off and pulse DC into the primary of the transformer.

You would get a pretty choppy AC with an uncontrolled frequency off the secondary of the transformer.

Amateur radio operators used to do this with car batteries long ago to get a higher voltage.

Think how a car ignition works. Same concept.
 
110624-1116 EDT

The answer is yes or no depending upon your definition of transformer.

Using a broad definition, see transform in dictionary.com , then the answer is yes.

Using a narrow definition, see item 2 under transformer in dictionary.com , then the answer is no.

If transformer means only two coils magnetically coupled and you are speaking of steady state DC to one coil, then you will not get steady state DC from the second coil in the real world.

If transformer means a black box with two input terminals and two output terminals, then the input can be either DC or AC and the output can be DC or AC. What the capability is depends upon what is inside the black box.

I believe the original post was assuming the narrow definition of transformer, and therefore the answer is no for a steady-state DC input.

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petersonra said:
Surprising to many, the answer is yes, and in fact was once pretty common.

What people would do is take a common relay and put its nc contact in series with its own coil.

A n/o contact would feed DC into the primary of an xfmr.

The relay would happily chatter on and off and pulse DC into the primary of the transformer.

You would get a pretty choppy AC with an uncontrolled frequency off the secondary of the transformer.

Amateur radio operators used to do this with car batteries long ago to get a higher voltage.

Think how a car ignition works. Same concept.
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That is also how the viberator in a vacuume tube car radio works. Six or 12 volts could be steped up and rectified to procuce the 3 or 400 volts needed to make a radio operate.

Some how the guy that first invented it put the words togeter to come up with Motorola for the system.
 
petersonra said:
Surprising to many, the answer is yes, and in fact was once pretty common.

What people would do is take a common relay and put its nc contact in series with its own coil.

A n/o contact would feed DC into the primary of an xfmr.

The relay would happily chatter on and off and pulse DC into the primary of the transformer.

You would get a pretty choppy AC with an uncontrolled frequency off the secondary of the transformer.

Amateur radio operators used to do this with car batteries long ago to get a higher voltage.

Think how a car ignition works. Same concept.
Click to expand...

Interesting, but is the answer to the OP yes? You won't be able to feed DC directly to a transformer and have AC on the secondary. What you've described is using a rough method of chopping the DC waveform and arriving at AC with some frequency as you described. Still pretty interesting :thumbsup:
Regarding Gar's comment, I've also encountered inverter and power converters being referred to as transformers, but I don't think the terminology is appropriate.
 
The voltage induced in a coil, say for example the primary of a transformer, is proportional to the rate at which the current is changing. For most of the systems we deal with, the current varies from max positive to max negative and back again 60 times every second. That is the "rate of change of current" that would create a voltage in the primary of a transformer.

But for the most part, "DC" current does not change. Its "Rate of Change" is zero. So the voltage it would create in the primary windings would also be zero. That would mean that there is nothing available to induce a voltage in the secondary. Thus, the secondary voltage would be zero. Thus, you don't get an AC waveform out, when your input is DC. What you get as an output is zero volts, and zero current.
 
charlie b said:
The voltage induced in a coil, say for example the primary of a transformer, is proportional to the rate at which the current is changing. For most of the systems we deal with, the current varies from max positive to max negative and back again 60 times every second. That is the "rate of change of current" that would create a voltage in the primary of a transformer.

But for the most part, "DC" current does not change. Its "Rate of Change" is zero. So the voltage it would create in the primary windings would also be zero. That would mean that there is nothing available to induce a voltage in the secondary. Thus, the secondary voltage would be zero. Thus, you don't get an AC waveform out, when your input is DC. What you get as an output is zero volts, and zero current.
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To follow up on charlies comments.

Induced voltage is a function of a changing magnetic flux with the flux being a function of the current as charlie mentioned. It is this changing magnetic flux in the primary that induces a voltage in the secondary windings.

With DC there is a magnetic field associated with the DC current however as charlie mentioned this is a steady or constant field. So with no changing magnetic flux in the primary there will be nothing to induce voltage in the secondary.

In simple terms voltage is proportional to di/dt. This is constant for DC.

I have seen electricians trying to megger the primary of a transformer with a DC megger trying to analyze readings for the secondary of a transformer. Simply does not work.
 
I'm not going to try to hang with some of you guys, but it seems to me that DC current does not change directions but it could change amplitude, and in fact is half a sine wave, with a full wave rectifier producing half sine waves at 120 Hertz. It is the Capacitor that usually follows that "fills in" between the peaks of the sine wave halves.

Seems to me that DC without the capacitor would probably do SOMETHING through a transformer.
 
I don't know what I did, but it seems my post is in the Nether world somewhere.

I think DC from a battery would cause an impulse when connected and disconnected, and dc from a full wave rectifier without a capacitor would do SOMETHING through a transformer

well there're my posts now... back from the ether
 
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120624-2148 EDT

Until you state what definition you want to use for the word transformer there will be an argument.

Because radio receiver vibrators were brought up and Motorola (Galvin) was mentioned as the inventor I decided to try to find the most basic patent for it. Unfortunately I can not search old US Patents for content. In fact tonight I had less luck with freepatentsonline.com than another time. I found some other Internet reference that implied that P. R. Mallory company may have been the inventor of the car radio vibrator power supply. There also was mention of a motor generator (dynamotor power supply) possibly used in the 1920s. Mention was that Ford installed or provided car radios as early as 1932. But also note that Ford worked with the Detroit Police in the 1920s with two way radio communication.

I was able to find patent 2,240,123 filed Sept 16, 1933 assigned to RCA for what appears as a means to reduce RF noise back into the car's wiring system. This uses a vibrator and likely a synchronous rectifier. I did not read the patent closely.

String searchable patents aren't available much before about 3,920,271 (1976), however everything from #1 is on-line, just not searchable. If you know the inventor's name, then it appears you can find old patents by this means.

I can find a very large number of patents by Marion Mallory of Mallory Research Co. These relate to internal combustion engines and many are ignition system patents. But it is not the P. R. Mallory Co.

There is a big difference between an automotive ignition coil and a vibrator type power supply.

.
 
When you apply a DC voltage to one side of a transformer the time while the magnetic flux is building generates a voltage in the other coil. And after the magnetic flux is saturated the voltage drops to zero.Now when you remove the voltage from this side of the transformer a voltage of opposite polarity is generated in the other side while the magnetic flux collapses.

That would have been one AC cycle not a perfect sine wave, that depends on all the other factors frequency, impedance and how long on and how long off as in pulsating. The DC has to be turned on and off.
 
Irishman89 said:
Good day Members, can someone please answer this for me?

Can DC c be converted to AC current through a step up transformer?

if yes, how?
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No. It requires the use of solid-state converter, commonly known as "inverter" or a rotary machinery known as "motor generator set".

What's the power source and what are you trying to power?
 
ronaldrc said:
When you apply a DC voltage to one side of a transformer the time while the magnetic flux is building generates a voltage in the other coil. And after the magnetic flux is saturated the voltage drops to zero.Now when you remove the voltage from this side of the transformer a voltage of opposite polarity is generated in the other side while the magnetic flux collapses.

That would have been one AC cycle not a perfect sine wave, that depends on all the other factors frequency, impedance and how long on and how long off as in pulsating. The DC has to be turned on and off.
Click to expand...

I don't think it has to be turned OFF ... just varied... Isn't that sort of what goes on with audio amplification? the AC is added to DC raising the AC to the point where the current doesn't alternate, but it does modulate.

And something that I didn't think of in my earlier post... the transformer winding would look pretty much like a short circuit to the DC... so it would have to be current limited somehow.

There's a whole lot involved with the whole deal that I am sure I don't understand, so I'm gonna back outta this thread saying that I think DC could be "transformed" with a step up transformer, but I don't know what could be done that would have any practical application using transformers designed for 60 Hz AC.

why not transform it first, and then rectify it?
 
110625-0800 EDT

realoman:

A unidirectional varying DC voltage or current into a transformer primary will produce the AC component on the output. As you have said.

When you do this there is a DC bias to the transformer core flux and an unbalanced hysteresis curve. Usually a transformer operated in this manner, a single-ended audio stage, will have more air gap in the core.

A push-pull stage has a center-tapped primary and thus cancels out the two DC components. The center-tapped primary is also what was used in the car radio radio power supply.

If you apply a balanced sq-wave input to a transformer, no DC component, and make the frequency low enough relative to the equivalent shunt inductance of the primary, then the output is approximately the calculus differential of the input sq-wave as somewhat described by electric-light above. His description brought in other factors. A single RC or RL circuit can be considered an approximation to an integrator or differentiator depending upon their connection, and the circuits are given these names when used in this fashion.

(For example if you want a pulse from the leading edge of a sq-wave, then you connect a small capacitor to the sq-wave, and to a low resistance load. 100 pfd to a 1000 ohm load produces about a 0.1 microsecond pulse. Obviously an exponential decay. A diode might be needed on the output side to remove the opposite polarity pulse from the opposite sq-wave edge.)

Back to the transformer. As you raise the frequency of the sq-wave the secondary output will become more identical in shape to the primary.

The design of the vibrator type radio power supply was essentially that of a class B audio amplifier. Each side of the primary was excited only 1/2 of the time. The output voltage was approximately turns ratio times battery voltage.

Ignition coils are also transformers to raise a lower voltage to a higher one, but on the primary side the core is driven hard and high up in magnetic flux. Basically charging the magnetic field. This is a fairly slow rise because of the primary L-R time constant. On the secondary there is an induced voltage that is something less than the battery voltage times the turns ratio. Really much smaller.

But the high voltage for the spark is generated when the primary current is interrupted and the rapid collapse of the magnetic field creates a large voltage across the primary (much larger than the battery voltage), 100s to a thousand volts across the primary. This large voltage times the turns ratio produces an even larger secondary voltage, maybe 30,000 volts open circuit.

The whole operating of the circuit is more complex because of distributed capacitance and non-perfect magnetic coupling from primary to secondary. There is also the capacitance on the primary to reduce arcing of the distributor points. Typically in engines the spark plug gap would breakdown in the 10,000 V range. Highly variable based on gap, sharp edges, and pressure.

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110625-0853 EDT

K8MHZ:

You do not get a DC component on the secondary side of an ignition coil without rectification. Put a resistive load on the secondary and steady-state, over many cycles, there is no DC component on the secondary side.

For any real world magnetic transformer there is no DC component transferred thru the magnetic transformer.

Take any magnetic transformer with separate primary and secondary coils and connect a Simpson 260 meter to the secondary. Now apply any repetitive wave form, including DC bias, with a fundamental frequency above the averaging time constant of the Simpson to the primary and you will read zero volts or amps on the secondary.

.
 
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