# Questions tagged [ac]

This tag refers to alternating current mains power. It usually applies to voltages with >100V RMS, but can also be used for ex. 24V industrial AC power.

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### Basic Training for working with 120V AC

I'm planning to build a digitally-controlled light dimmer circuit. I'm not trained in electrical engineering, and I don't want to do something that an electrician would immediately recognize as ...
12k views

### AC polarity detection

How can I detect AC 'reverse polarity' (single phase) (without the use of ground/earth) and drive a led when the polarity is reversed? It should at least detect 230 VAC but it would be cool/...
3k views

### Why does this optocoupler circuit work without getting destroyed?

This circuit is being used for mains detection. Input is being fed directly from 220V 50Hz mains and output goes to Arduino which is running on 3.3V. Theoretically the optocoupler LED should burn out ...
3k views

### How do I design a current transformer?

I want to make a Current transformer using toroidal ferrites to measure 220/50-60Hz AC current(40A max). Is it possible? And how can I calculate secondary turns count? Ferrite properties: H = 2000, ...
1k views

### How to limit current of an AC signal

For my project, I'm trying to work with the principle of electrovibration. This principle is about simulating textures using low current electricity on an insulated conductive surface (see Wikipedia). ...
928 views

### Are we close to a pure DC (or hybrid) household? [closed]

This is a philosophical question. Over the last few years, many of the household devices, particularly those that are more mobile and etc are DC devices. Are we at some point where a DC household may ...
610 views

### Understanding this AC coupled circuit

I'm having a little trouble understanding this circuit and could use some help. So far I understand that this is an AC coupled circuit, and the capacitor is a blocking capacitor. I also know that ...
12k views

### Capacitive AC voltage detection

As I understand it, a non-contact voltage tester works by creating a capacitive connection from a power line to ground, via the detection circuit and the operator's hand/body. This connection passes a ...
325 views

### Trouble with Schimtt trigger settings for varying sinusoidal inputs

To make my problem easier to describe, I drew the above figures (abbreviated as Fig.). The sinusoidal input comes from a rotating device, from a small alternator(a permanent magnet AC generator). ...
4k views

### Low Voltage AC Smoothing Capacitor Calculation

I have a 9V AC source which will have a max load of 100mA. I'm trying to figure the value of a smoothing capacitor with less than a 10% ripple. I don't have a scope or else I'd just try a bunch out. ...
4k views

### what do I need to make 230V AC fan spin slower?

So - i often work with DC current for robotics and the like, but now i have the problem that i'm having a 230V AC fan which shall be operated at two different speeds for an exhibition installation. I ...
2k views

### LED light dimming, TRIAC vs PWM?

Many days ago, I published a question here asking about dimming an AC LED using and Arduino and TRIAC, and I was told that most LEDs that support dimming should work with the circuit I linked to them. ...
505 views

### Need advices on an AC fan control circuit

I've setup a small system where I can control an AC Fan by a data-acquisition board's DAC. Here is my final schematics(please left-click to enlarge it): The first issue was to hack the manual speed ...
1k views

### Can connecting of AC adaptor first into device, then into mains pose a risk of voltage spike?

Manuals of several various electronic devices I came across recommend connecting their AC adaptor first into the device, then into mains. I always thought the reverse order is safer because I thought ...
1k views

### Neophyte question about AC vs. DC (especially for powering a home)

Here in the United States the electricity grid is AC. I have heard that AC allows transmission of power at greater distances with less loss. However, with the advent of solar panels, it would seem ...
2k views

### Grounded AC-DC power supply, what connects to earth ground?

In an AC-DC power supply, how is earth ground typically used? Take a common PC power supply as an example, does the earth ground connect to the metal chassis? Does it connect to the DC ground on the ...
3k views

### What does 'random phase' means in a triac driver?

I'm using this triac driver to control a triac. In its datasheet it says 'provide random phase control of high current triacs [...]'. What does that mean? It doesn't have zero-crossing detection?
574 views

### Symmetric power sockets – design considerations in electrical devices

There are various single-phase power socket standards in use. Some countries use plugs that can be plugged in the socket only in a specific orientation (for example, the United Kingdom) while other ...
271 views

### Which relay will last the longest?

I'd like to control a 20 amp, 240 volt AC resistive load with a heavy duty contactor. The contactor I have is a Siemens 3TX7130-0DB03 rated for 30 amps, and DPDT. I was originally going to switch ...
6k views

### Is there any option to store AC voltage?

Almost every power plants produce Alternating current. It is not necessary that entire energy that they produced are consumed in real time. Does they have any option to store excess energy?
927 views

### How do capacitors improve power factor without destroying the capacitor?

Can anybody help explain in simple terms how adding capacitors to a 120/240/higher AC power circuit helps improve power factor without blowing up the capacitor? I'm familiar with capacitors in DC ...
11k views

### Why is there alternating current in my wall socket?

Why is the standard of delivering electricity to our homes is via alternating current, and not direct? As far as I know almost every electronic device has an AC»DC converter because their internals ...
5k views

### Dimmable AC LED controlled by Arduino

I am a beginner, and I have a school project that requires me to use Arduino or any other microcontroller to control an LED light. After some research, I found out that not all LEDs support dimming, ...
157 views

### How can I build BJT amplifier with Vin and Vout requirements (peak to peak values)

I have been working on a project but I'm not sure if I'm complying with the requirements that I was given. Design a BJT amplifier such that VIN=0.1 V and VOUT=5 V (peak to peak values). ...
204 views

### math behind complex numbers C||RLC

I have a mathematical problem with the following formula. The goal is to transform this equation to have a seperated real and imaginary part. I have already done this with several other equasions, but ...
442 views

### Measuring an AC-voltage at the ouput of a full bridge rectifier

I've a full bridge rectifier and I put the following function into it: $$5\sin(100\pi t)\tag1$$ So, at the output I get: $$\left|(5-2V_d)\sin(100\pi t)\right|\tag2$$ Where $V_d$ is the voltage ...
130 views

### Loop of a wire and right hand rule

When the loop is the figure shown below will be rotated in clockwise direction the the slip ring connected to the red segment of the loop will give us the positive voltage and the slip ring connected ...
2k views

### Can Average Power of a 3-Phase AC motor be calculated from Mean Current & Voltage RMS from each winding?

If this is possible could a formula be provided. + Explaination. Thanks very much in advance. FYI I am completely new to this site so please be kind. Could I ask that any criticism be constructive. ...
1k views

### Importance of series resistor at output of Rectifier

For conversion of AC into pulsating DC we used Rectifiers circuits. But I read somewhere (from a well-known site) that the circuit does not work in ideal condition if I used my first circuit. The ...
3k views

### Synchronising Power & Synchronising Coefficient

I am really confused with the concept of synchronising power and synchronising coefficient. I was taught 2 simple formulae in class. P = 3VEsin(del)/X Sp = dP/d(del) = 3VEcos(del)/X Now, I am ...
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### Transformerless power Supply - 24VDC, 120V AC and 230V AC

I want to know if it is possible to design a power supply for a circuit that can operate from DC and AC using the same input terminals. Thus, the output should be xxV DC (5-24 or whatever is decided ...
1k views

### Calculating the value of the resistance for controlling the speed of AC fan

i have an ac fan that i would like to control its speed i am a bit new in this field so please bear with me i had the idea of fixing 3 speeds with 3 switches one for each speed: (25% 50% 90%), ...
3k views

### What wattage solar panel required for AC 1000 watts

If my house load is 1000 Watts AC/220V, then 1000 Watts DC/12V solar panels is not enough. What wattage solar panel would be required for AC 1000 watts?
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### Converting 2 pin plug into a 3 pin grounded plug [closed]

I have a portable power socket that accepts two 2 pin power plugs and 1 pin 3 pin grounded power plug. There is a hole on one side of this portable power socket where the wire goes into. Oddly this ...
127 views

### Question about AC servo motor driver

Does anyone know what means when AC servo motor driver displays error code for "regenerative discharge", and stops working. What this mean in practical situation. This happens from 1 to 10 minuts ...
46k views

### Why are home appliances and other devices made to operate on dc? [closed]

Why are home appliances not designed to work on ac?why cant we just stepdown the incoming 230V and design the systems to operate at low ac voltages,instead of converting ac to dc?
28k views

### Why use complex numbers to represent amplitude and phase of AC

Why is it that in AC circuits, sine waves are represented as a complex number in polar form? I don't logically understand from a physical perspective why there is an imaginary part at all. Is it ...
19k views

### Why do we use $s=j\omega$ in AC analysis instead of $s=\sigma+j\omega$?

In AC analysis, $s=j\omega$ when we deal with $sL$ or $1/sC$. But for a Laplace transform, $s=\sigma+j\omega$. Sorry for being ambiguous but I would like to connect the questions below: Why ...
29k views

### Why is sine wave preferred over other waveforms?

Why did scientists chose to go with sine wave to represent alternating current and not other waveforms like triangle and square? What advantage does sine offers above other waveforms in representing ...
82k views

### Difference between Line and Neutral in AC

I want to find out what is the difference between the AC (220 VAC) lines, (phase and Neutral). As I know that the Alternating Current (AC) has no polarity, so why do we have a "phase" line and a "...
8k views

### 24VAC/5VDC power supply design

I am planning to create a water valve controller using an MCU and a set of solenoid-controlled valves. The solenoids run on 24VAC (40mA inrush, 20mA holding). The MCU is on a board that draws ~100mA, ...
62k views

### AC to DC without transformer. How does this thing work?

I disassembled a Chinese-made flashlight and found they use just capacitors to bring down the voltage instead of a transformer. They are using it to charge small lead-acid battery. My question is how ...
33k views

### Does AC Power have Polarity?

When I run 24VAC into a full wave bridge rectifier followed by a 220uF electrolytic capacitor to turn it into ~32VDC, the source has two wires. Does it matter in what order I connect the AC wires to ...
18k views

### Reflecting impedance in a transformer

Please can anyone tell me what exactly is meant by reflecting of impedance in a transformer? I do not know much about transformers, but I want to know about its uses and phenomena behind it. I will ...
2k views

### Instantaneous vector sum of three phases 120 apart is not zero?

Vector sum of equal 3 phases 120 degree apart is zero and serves as a neutral. However, while drawing instantaneous vectors of the three phases, they summed up all together to give a vector. I have ...
16k views

### Schuko plug wiring

Why it is not important where we connect our hot and neutral wire when connecting them to our Schuko plug? Is it because current flows in both directions? It is only important that our ground wire is ...
3k views

### How can there be a current without a voltage?

Recently while trying to understand inductive AC circuits better, I got very confused with a question. Let's suppose we have a purely inductive AC circuit with ideal wires and a switch. Let's also ...
521 views

### What is the name for PCB mount AC power connectors

What is the search keyword for PCB mount AC power connectors? I'm looking for just the metal connectors (plug and receptacle) for solder to the PCB. I'm asking for the brass connectors shown above. "...