Hello forum,I have a question pertaining to transformers. I understand the current oscillating in a coil of wires around a toroid-type metal induces a moving magnetic field in the metal, which induces current in another set of coils on the other side, right? If I'm slightly correct, yay1) Are transformers specifically AC? Can there be DC transformers or would I have to rectify it after it's been stepped-down?2) Is the output voltage independent of the current? Let's say I have 50W, 120V stepped-up to 240V. If I change the power supply to 100W, will the voltage still be stepped up the same, while current would be twice as high? (Ideally)Thanks!
transformers work only with AC Voltage is mostly independent of current or power, as long as you stay within the ratings of the transformer maximum values. Even within those values, you will see some drop in voltage as you increase current due to internal resistance of the winding. For example, if you have a 240 volt 1 amp secondary, the voltage out may be no load 250 volts 0.5 amp load 245 volts 1.0 amp load 240 volts 1.5 amp load 220 volts (and getting hot)
Transformers can work on dc if you oscillate the pulse. a steady dc voltage will not produce the any inducement. a simple 555 timer will work on small dc voltages. for larger voltages you could actually use an on/off switch and switch it manually very fast. High voltage oscillators are available. But rectifying is not necessary
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A transformer is just a double inductor an inductor that uses the magnetic field generated by moving electrons to move OTHER electrons (in the other coil). But the magnetic field must itself move, in order to move those other electrons. With DC, the electrons are moving at a fairly constant rate, so they produce a fairly static magnetic field. It's not enough to know that moving electrons produce a magnetic field; you have to see that the electrons require more than a velocity; they require an ACCELERATION (time rate of change of the velocity) in order to make the magnetic field also change. So you can see immediately from the physics of the matter, that transformers are only useful for AC, since you want the electrons in the secondary coil to be oscillated by the moving magnetic field from the oscillation of the electrons in the primary coil. Inductors are useful, but they are also AC devices. There are some uses in DC circuitry, since DC voltages do change in response to external events (like when the system is turned on, or when there's a variable load) but largely these uses are semi-static.
Lines of force. That is what defines what and how transformers work. The material and configuration of a transformer govern it's efficiency. A torroid is more efficient than a transformer formed from alternating stacks of grain oriented steel. Copper wire is more efficient than aluminum because of lower resistance. Silver would be better but too expensive. Your Physics book says that 1:1 turns give a 1:1 voltage transfer. It does if the proper number of turns are used to provide the right number of lines of force, There is a certain amount lost to resistance and eddy current losses in the transformer core. When you introduce DC into the core, you interfere with the transfer of the AC voltage. A small amount of DC can saturate a transformer and stop it from working or control the way it works. Called a saturable reactor, this method was used to control many power systems before triac and SCR control systems took over. Your ignition (Kettering system) works by intoducing a DV voltage into a step up transformer and then cutting it off. A typical system used to use a 1:400 turns ratio to work.
