Right, so that an asymetric ac is produced. The positive cycle to be half AC and the negative more like a squared ac.The passive components you mention have a symmetrical characteristic and don't show any rectifying effect. A principle way to get some kind of rectifying effect would be a saturated reactor with DC premagnetization, using a permanent magnet.
This sounds as though it's similar to the magnetic amplifier, a method of feeding small DC current through an auxiliary winding, to control power through the main winding.
I have yet to experiment with the concept, but you may find a way to saturate the flux to one polarity or the other. The result could be partial or total rectification of AC.
Hi, this is a kind of weird question. I was wondering if I can take only the positive pulses out of the AC mains (after a step down transformer) but using only transformers, capacitors, coils and resistors. No semiconductor or tube.
A way is the synchronous rectifier using either relays or motors, but I was wondering if this can be done my some king of saturated reactor or anything else comes to your mind so that mechanical movement can be avoided?
Are there historically such attempts?
The passive components you mention have a symmetrical characteristic and don't show any rectifying effect. A principle way to get some kind of rectifying effect would be a saturated reactor with DC premagnetization, using a permanent magnet.
If you draw net DC from a transformer with a single output diode for example this will be reflected in the mains input current, there is a limit of 5mA average you may draw from the mains supply for reasons of earth stake corrosion. Also if you draw enough DC from the mains you will cause asymmetry on the mains waveform and this can lead to local transformers drawing excess current (flux stair casing) blowing their fuses and breakers....
Will there be DC in the mains input of a transformer with a single output diode?
The secondary DC current will cause a strong DC flux component which in turn enforces an asymmetrical magnetizing current.The secondary current will not change the magnetic flux in the iron core.
Correct, every time, ever plugged in a hair dryer on half power (achieved with a diode in series with the element) and noticed a local transformer buzzing when you do this?
I guess less than 1 mA if the transformer is suffciently far from saturation.What would be the typical approximate magnitude of the DC current in the primary?
I guess less than 1 mA if the transformer is suffciently far from saturation.
The question about the expectable primary DC current hasn't been answered yet. My < 1 mA guess was extrapolated from a measurement with a small (20 VA) transformer and a half-wave rectifier DC load of about 50% Irated. Obviously this transformer is operating at a low core flux.Give me a feel for the magnitude of the effect. Suppose I have a suitably large 1 to 1 isolation transformer and I connect the secondary to a 50Ω resistor in series with a diode. I would expect a current of about 2.4 amps (in the U.S., with 120 VAC at the outlets in the home) without a diode, so about 1.2 amps (RMS, AC+DC) with the diode.
It does depend on the design of the Tx and how far towards Bsat it goes normally. Also the type of Tx, e.g. toroidal is much worse than EI. For a 3kVA isolation Tx, with Bpk = 1.8T say, with normal transformer steel material, drawing 1.2 amps rms via a diode, could easily lead to 10 amps peaks in the primary as the resistance of the wires is low. Try it your self...!
Ok. Suppose the transformer is a 1 kW isolation transformer with E-I laminations, loaded as I described in post #12. Typically, what DC current would one expect in the primary?
unfortunately we have steel cored transformers which are non linear...A linear transformer can't transmit any DC component to the primary side in steady state
And you may get saturation when input "voltage" is unsymmetric = has DC components.
But this is not the case when secondary current is unsymmetric = DC current components.
Imagine a flyback transformer has a catch diode at its secondary. Here the current is only in one direction. It can't flow in reverse.
Also you may use a diode at a standard transformer secondary output. Whithout (big) core flux change.
The core flux is proportional to the integral of voltage over time. Not current.
But in detail an unsymmetric current on the secondary side will cause an unsymmetric current on the primary side. Now any power source has series impedance Lets say 0.5 ohms with a 230V system. And if the unsymmetric current is 5A, this causes a 2.5V DC component at the primary side. And thus the core sees a small DC component and therefore thre will be increased current in the opposite side (increasing slowly over a lot of fullwaves). It will compensate the unsymmetric current a little, but not completely.
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