1. ### Engineering How does this Bipolar RF Amplifier + Output Transformer circuit work?

I am trying to create a receiver for a personal project I am working on. This is the RF amplifier that I was given by a book I am following. How does this circuit work? Usually for a BJT amplifier I find the DC bias point and then use the small signal model after I bias the circuit? I understand...
2. ### B DIY Electromagnetic Induction Experiment

So I was watching this video containing DIY experiments on electromagnetic induction . At minute 4:45, the dude pretty much creates a transformer without using an iron core. He runs 30-50 kHz AC in a coil (forming the primary circuit) and then brings another coil with its ends attached to a...
3. ### Engineering Voltages, currents and power between a power plant and a transformer

This is the first part of the problem, which I solved. Now to the second part which I can't manage to find the equations I need to use. Problem: This plant is connected to a 20/0.4 kV transformer of 250 kVA power, through an XP00-A cable (4x150 mm2, IN=300 A, Z1=0.26 Ω/km). a) Calculate...
4. ### 12AC to +/- 12DC transformer

I can't seem to find a transformer that simply converts a low voltage 9V-12VAC to a center tapped output to get +/- 9v/12VDC. It seems all power transformers have a 120VAC input voltage and the lower voltage transformers are designed for high frequency switching. What is a low voltage to low...
5. ### How can Center-tapped Transformer parameters be found?

It is a common center-tap transformer which is electrically demonstrated as in figure (ideal one); In my opinion, open circuit and short circuit tests cannot be applied directly. How can I place secondary reactances ? And how can I test its all parameters in laboratory ?
6. ### I Biot Savart Law with Different Magnetic Permeabilities

I would like to make a program that produces a 2D heat map showing the magnitude of the magnetic field produced by a finite length solenoid. The heat map would show the field strength along the radial and axial directions of the solenoid. I plan to divide the conductor into "infinitessimally"...
7. ### B How a Secondary Resistor affects the Transformer Primary Side?

Let's assume a 2:1 transformer which has a 100V Source connected on the primary circuit and has no/negligible resistance, on the secondary circuit a 5 Ohms resistor is connected. Using the 'Impedance Transfer/Reflection' method, the primary circuit would act as if there was a 25 Ohms resistor...
8. ### 415V to 11kV Transformer Voltage % regulation

1. Homework Statement A 415V to 11 kV transformer has a rating of 200 kVA. The winding resistance and leakage reactance when referred to the primary are 0.014 Ω and 0.057 Ω respectively. (a) Determine the % regulation of the transformer at 0.8 power factor lagging. (b) In designing a...
9. ### Engineering Parameters of transformers: open and short-circuit tests

Homework Statement Ok I have the following circuit and data (when the subscript is "ef" it means "rms" values): I am asked to determine the parameters of the transformer r1 L11, L22 and LM with the given experimental data. Homework Equations 3. The Attempt at a Solution [/B] I had no...
10. ### How do transformers work, and how to read dot notation

<Moderator's note: Moved from a technical forum and thus no template.> Hi all, I have attempted this question but have a few queries on how transformers work, and what the dot notation represents. (a) The flux would be clockwise around the iron core. (b) This is the question where it gets a...
11. ### Why are there three wires in secondary coil of transformer?

This is a 12-0-12 transformer that I intend to use in my circuit: Why are there three wires in the secondary? One is of course the neutral (in black). Why are there two live wires? As an additional question, can I use four 1N5408 rectifier diodes to convert the output of this transformer to...
12. ### Question about Magnetic Circuits in a Transformer Core

Hello community, I can't find an explanation for something and I thought I'd come and ask you. I'm studying for a test I have tomorrow and I came across a problem of a three legged steel core with 400 turns on the center leg, the magnetization curve is given, the first part of the problem asks...
13. ### Easy way to calculate losses for re-purposing a transformer?

Hi everyone! This is my first thread :) I've been working a bit with AC and radio, and would like to make a simple(-ish) circuit in which a 1-volt peak audio signal is stepped up to around 5 volts with a transformer, and is fed into a crystal oscillator to make a crude-but-effective AM...
14. ### I Phase differences in Transformers

How is the phase difference between the current in the primary coil and induced e.m.f. in the secondary coil be 90*??
15. ### I Short Circuiting the Secondary of a Transformer/Self Impedence

Thank you for reading my post. I was watching the video this video on transformers and saw an amazing demo: From 4:00-5:20 the guy does an experiment where he has a simple transformer circuit set up: On the primary side of the transformer he has an AC power supply, and a lightbulb. On the...
16. ### Switch mode DC transformer equations?

I would like to know if there are any general equations (such as the AC transformer equations) that describe a switch mode DC transformer. By this i mean a constant frequency DC signal (50% duty cycle) that ranges from 0V to some max voltage on the primary coil and outputs some higher voltage on...
17. ### Two AC Sources with One Transformer

I want to program a little power grid game and have the problem of connecting things via transformers. Imagine the following setup: You can see the AC voltage sources as generators (or together with the resistor as a "consumer", if the amplitude is 0). What I need to figure out are the...
18. ### How do I interlock 2 CFL, a buzzer with the opening of door? Read description...

I have a transformer chamber with 2 doors. What I have to do- If any of the door is opened, this should happen- 1. 2 CFL inside transformer chamber should start 2. Simultaneously, a buzzer/hooter should be ON. 3. After opening the door, I should have option to reset the hooter. how do I do it?
19. ### Current and power with transformers

Homework Statement I am working on the following problem: And ideal single phase transformer 240V/2880V is supplied with a 240V source via a resistance cable of 3ohm. If we connect a R=720ohm resistance to this, determine the primary current and the dissipated power in R. (I'm sorry if some...
20. ### High-frequency transformers - how are they different?

I apologize for being somewhat scatter-brained here, I just have too many questions on this topic. I know high-frequency transformers use ferrite cores instead of laminated silicon-steel, but what other differences are there? Does their reactance still follow the standard formula: 2*Pi*F*L ...
21. ### Mains transformer with 1.4 ohm primary winding?

I don't understand how this is possible. This is a rather large transformer in a stereo system amplifier. The transformer is a simple step-down with 120V mains primary to a center-tapped secondary providing both 38V and 76V. According to ohm's law, at 120V this thing should draw about 85 amps...
22. ### Booster transformer topology for transmission application

Hi, Regarding transmission line booster transformer topologies I'm curious as to what would happen over all the possible permutations. I refer you to the following: http://top10electrical.blogspot.com.au/2015/03/booster-transformer.html I presume that in real life the booster transformers...
23. ### DC12V 12A car window motor - what spec for a 220V PSU?

I have a combined motor and screw drive (to 90 deg). It's original purpose was to convert car windows to electric drive... my guess is that it is at least 25 years old, and made in Japan. For scale... the width of the motor casing is 50mm (as you look at it) I'm making a motorised turntable...
24. ### Electrical Efficiency of Ionized Air?

Alright It's been over a year since I've posted and received amazing help the last time I did. Now I've a question I cannot seem to find an answer to. Say you have an electrical charge and use a transformer to step up the voltage high enough to where it arcs in air. Then you have a conductive...
25. ### Dumb question regarding short circuit test equivalent resistance

Hi, Silly little question about the transformer short circuit test. When I perform it with the secondary shorted and I get Req = Power / current2 is this Req = Rpri + Rsec? If I measured Rpri and Rsec with a multimeter? Thanks
26. ### Variable 100-350VAC output controlled by PLC?

Hello, I have a strange request from a client. He has a "burn-off" which is used to burn bits of labels that are stuck onto his products, that's a bit vague, but it's all the info I have. The request is that he wants to be able to change the voltage going through the burn-off anywhere between...
27. ### I Autotransformer: Why does primary current go through coil?

Hi. Why is it that in an autotransformer apparently most of the primary current goes through the winding and not through the load?
28. ### Calculating Input Voltage of a Step Down Transformer

Homework Statement A pair of power transmission lines each have 0.68-Ω resistance and carry 650 Amp. If the primary voltage of the 10:1 step-up transformer is 4.6 kV, calculate the input voltage of the step-down transformer at the other end. Homework Equations P=IV V=IR IpVp = IsVs The...
29. ### Primary magnetizing impedance of non-ideal transformer

I am trying to determine the primary magnetizing inductance + core shunt resistance of a transformer. I attached the equivalent circuit of the transformer. I left the secondary open and have an AC voltage on the primary. This causes the coupling leakage inductance and coil resistance to appear...
30. ### Magnetic flux and current directions of transformer

Hello. Let's take a transformer picture first. The basic equation explaining how the transformer work is the equation of Faraday's law of induction. \begin{array}{*{20}{c}} {{V_P} = - {N_P}\frac{{d{{\rm{\Phi }}_B}}}{{dt}}\;\;\;\;\left( 1 \right).}\\ {{V_S} = - {N_S}\frac{{d{{\rm{\Phi...