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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Is this method of proving energy is conserved in an LC oscillator correct?

Assuming no energy loss due to heat or EM waves $$U=\frac{Q^2}{2C} +\frac{LI^2}{2}$$ differentiating both sides with respect to time, $$\frac{dU}{dt}=\frac{QdQ}{Cdt}+IL\frac{dI}{dT}$$ but we know that ...
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Three-phase AC motor LTspice simulation

I am wondering if anyone has an idea of how I can model a three-phase AC motor in LTspice. I have linked the characteristics of the motor below and it will be connected to a three-phase inverter.
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Does AC input polarity matter if you are connecting it to an LED fixture with its own AC-DC converter? [closed]

I was installing LED lighting in my garage, everything was going great. I connected one lamp and tested it. When I installed the second one, its capacitor blew out but it did not stop working. The ...
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1 answer
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AC signal switch with MCU [closed]

I need to switch an AC signal (0.3 to 1 V) with a 3.3 V MCU and I have no idea on how to proceed. Could someone point me in the right direction or propose a circuit? My last idea is to use a relay, ...
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1 answer
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Multiple AC-DC power supplies: one direct AC wall plug or two?

I'm building a data acquisition system that needs to power sensors and a high voltage contactor at 24Vdc, 12Vdc, and 5Vdc. After reading another post, it seems it is best to use separate AC-DC power ...
1 vote
2 answers
80 views

Externally sensing if AC current is being drawn over a power cord [duplicate]

For a DIY project, I would like to know the on/off state of a load (on being over around 200 mA, otherwise off). For example, a smart home app tells a smart switch to turn on a fan that's connected to ...
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2 answers
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Can 12V/9V DC source be used for Christmas Disco Light instead of 220V AC?

the Christmas disco lights up on 220V AC supply. Now, can I used 12V/9V DC at the points A and B (picture attached)? And, will the lights work as before in AC source supply? If not, please enlighten ...
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AC/AC power supply for PCB

I am trying to source the right setup for powering this PCB: I have found an 18 V AC/AC power supply but it has a barrel connector: I am struggling to work out how to connect the barrel connector to ...
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3 answers
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How to add a DOWN limit switch to a Harbor Freight (Pittsburgh) hoist [closed]

I am using a pittsburgh hoist to raise and lower a large curtain. The hoist has a built in limit switch to stop when it raises to a certain point. I need to add another limit switch to stop the hoist ...
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1 answer
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Problems running 110 V and 24 V PLC signals in same cable

Has anyone encountered issues running analog signals that are 110 VAC and 24 VDC together in the same cable on the way to their PLC inputs? Let's imagine each signal could be like 100 mA. I know with ...
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2 answers
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If the current has changed directions, why is it still positive in a negative half wave rectifier?

I have simulated a simple half wave rectifier circuit and plotted the current in the circuit and the voltage across the load resistor of 4 kilo ohms. The diode is an ideal one. The alternating voltage ...
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2 answers
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AC to DC 6 V for bicycle and super capacitors for lights

I’m trying to design a circuit to enable my bicycle lights and also have at least 2 minutes of standing lights coming from a bicycle 6 V AC hub. I thought about building a rectifier bridge with 4 ...
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"Pull-Down Resistor" in AC circuit

Background I have an Fridland AC doorbell that I am about to make "smart". My approach is to connect a device named a shelly uni inside the doorbell that ...
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Reading 2.5 VAC with Arduino analog pin - circuit review

I am trying to read AC voltage with an Arduino to be able to detect parameters such as phase angle, peak voltage on load and source sides for comparision. For this, I have a 230VAC to 15VAC ...
1 vote
1 answer
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Blower motor run capacitor connected to neutral instead of hot/line?

While troubleshooting an issue with my downdraft range vent external blower unit (Kitchenaid KPED829K. ~20 years old. Motor model: ebm-papst R4E310-AL15-10 ) I noticed that the start and run capacitor ...
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1 answer
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Three diodes in series AC detection

Why, in the circuit shown here, would you put three diodes in series with one another instead of using one diode?
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2 answers
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Is it safe to connect DC equipment to a charging battery?

I have an off-grid house with a central 24 V setup of batteries and solar panels. During the day, the voltage of those batteries changes quite a lot, based on power consumption and the solar panels' ...
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7 votes
6 answers
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How to know if this is a band-pass filter?

I have the circuit below. How can I see that it is a band-pass filter? I tried calculating the equivalent impedance for the parallel part of the circuit: $$\bar{Z}_{parallel} = \frac{\bar{Z}_C\bar{Z}...
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2 votes
1 answer
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Phasor calculation doubles frequency?

When working with phasors we have $$\bar{Z} = A\cos(\omega t + \phi) = Re(Ae^{j(\omega t + \phi)}) = Re(Ae^{j\phi}e^{j\omega t})$$ where $$\bar{P}_1 = Ae^{j\phi}$$ is the phasor. But when we multiply ...
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3 answers
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AC voltmeter circuit

I was searching a way to get the VRMS of an AC voltage. The main transformer drops down the 230 VAC to 15 VAC and with a potentiometer I'd like to display it on a DC digital voltmeter (the AC ...
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How do you find the inductance in this AC circuit?

So far I can think of only one equation for a) So XL=2.(3.14)fL Then rearrange L=2.(3.14).50.XL If I know L then I can do the rest of this problem
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Isolation problem in AC current sensing circuit

I am working on an electronic project where I have to measure AC current. While searching, I often encountered a term called "isolation", especially when using the shunt resistor. What is ...
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Shunt resistor for AC current measurement

I am working on a power meter project where I want to measure an AC current using a shunt resistor. After research, I found that the use of this resistance is rarely. Is it possible to know the reason ...
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1 answer
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Speed control of a PSC induction motor, how does it actually work?

I'm trying to understand the physics and engineering behind speed control on PSC induction motors, usually seen in fans/HVACs. I have come across this link, but I don't quite understand everything ...
6 votes
2 answers
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Mains frequency meter using an optocoupler

I built a frequency counter using an ESP32 to measure frequency in Hz. To measure mains frequency, I used a PC817 optocoupler. First I drove the LED of the optocoupler using 3.3 V PWM signal and ...
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How do I derive the equation for current as a function of time \$I(t)\$ through resistor in this CLCR circuit schematic with a sine wave AC source? [duplicate]

How do I derive \$I(t)\$ through the resistor for the circuit schematic below? What method should be used. So far, I have tried mesh analysis for the 3 meshes using KVL but the system of equations ...
2 votes
2 answers
433 views

Can a non-invasive AC current sensor measure DC current? [closed]

Can a non-invasive AC current sensor measure DC current? What is the theory behind it?
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8 votes
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Why doesn't an AC solenoid coil change magnetic polarity on each cycle?

I am trying to figure out how an AC solenoid coil maintains its N and S magnetic polarity. Since in a sinusoidal AC, current alternates in both directions. How does the solenoid not change polarity (N ...
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How can I regulate 220 Vac fans with a microcontroller?

I need to control some 220 Vac fans. The fans are PAPST 4650N and I would like to control the speed using a simple MCU like an ATmega328P. I'm not interested in fine speed control, I only need to have ...
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3 answers
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Simple transformer construction help

I’m trying to construct a small transformer to step up the audio of a crystal radio to line level. I can actually hear the radio faintly using a conventional earbud (not piezoelectric), but I’d like ...
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Can high frequency AC show as DC on a multimeter?

If a high frequency AC (4kHz) is measured with the DC option on a multimeter, will it show a DC value?
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How does neutral in single phase AC work?

How does neutral in a normal one-phase outlet work? I looked on the internet and I know it carries the current back to the source, but does it do that in the inverse of the phase or does it provide no ...
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Using AC solenoids with rectified DC [closed]

If one wanted to avoid triac opto-couplers for AC solenoids, would it be OK to rectify the AC, without filter capacitance or regulation, then drive from a transistor opto-coupler? I would think the ...
1 vote
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High-voltage resistors versus anti-surge resistors

I am making a voltage divider with four 1M 1206 thick-film resistors and a single 2.7k resistor. The input to this voltage divider will be mains line and neutral. I want to measure the voltage at line ...
2 votes
2 answers
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What's the purpose of the form b in 4a1b relay?

This relay AHER4191 has contact arrangement 4formA + 1formB. I know the 4formA (pin 9~12 pin 1~4) are for L1/L2/L3/N lines but don't quite understand in which scenario the 1formB (pin5, 8) may be used?...
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Determine the absorbed complex power (AC Circuit Power Analysis)

I've been trying to solve a book problem from Hayt, et al. Engineering Circuit Analysis (8th Ed.) —Practice Problem 11.9. And here's my latest attempt, I just can't see what I'm doing wrong, why I ...
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2 answers
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Sizing a RC Snubber - microcontroller restarting when switching off an inductive load

I'm trying to drive an 220 V solenoid water valve with a relay, but I'm having problems: when I turn off the solenoid, the microcontroller reboots. I believe the source of the problem is the spike ...
1 vote
2 answers
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What is the electrical circuit symbol for an "AC ground lifter" or "cheater plug"?

This is also known as a "three-prong/two-prong adapter." What is the electrical circuit symbol for this item? Here is an example: EDIT: To be clear, I am not using, nor endorsing the use ...
1 vote
1 answer
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Designing AC kick solenoid lock

I am making a kick solenoid lock with AC. I designed the circuit to run on 220 V, 50 Hz (household plug.) The inductor (coil) is air core 500 turns, 150 meter (500 ft) in length with inductive ...
1 vote
1 answer
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Why does PSPice invert this AC current?

I'm running a simulation on a simple circuit in PSPice 9.1: This voltage supply is set to provide a 1V AC signal with a frequency of 60 Hz. As the load is only resistive, the current should not have ...
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Why does this split-phase generator allow more current for line-to-neutral voltage than for line-to-line voltage?

I understand thoroughly the power equations for balanced sinusoidal three-phase circuits. I haven't studied split-phase systems that much, but I think I understand how the power equations would be. I ...
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10 votes
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What's the use of the 100 kΩ resistors in this schematic?

I saw a schematic for measuring AC voltage on a 3-phase mains supply (R/Y/B are the 3 phases and N is the neutral) I understand that the 1 MΩ and 2.7 kΩ resistors are for stepping down the voltage (...
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What's the difference between AC and DC and why do we need them both? [closed]

I read so many articles on the subject and still can't get the difference between AC and DC. I know that, for example, light bulbs in my house glow using AC. Why don't they use DC? Why does our house ...
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1 answer
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How does a 120V wall outlet accommodate to a 240V electric dryer? [closed]

I am beginner learning electronics and I started to learn AC. I've learnt that a US wall outlet provides 120V, however, I've googled that electric dryers are usually rated at 240V. So how would a US ...
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1 vote
2 answers
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What is this strange harmonic content present in a resonant circuit output waveform?

The following is an LC circuit excited at resonant frequency 15.915Hz (L=10mH, C=10mF.) I would expect the output to have only the resonant frequency (constantly increasing in amplitude) since the AC ...
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Find capacitance such that voltage and current are in phase

I just cannot solve this exercice, any help? This is what I have tried:
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Pure Sine Inverters and Transformer Selection

So I'm trying to design a 24V to 110V pure sine wave inverter, which I'd like to be able to do 2000W to handle running my portable A/C on battery. I get the whole H-Bridge MOSFET concept, and even ...
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How to visually display 3 phase output

We have inherited a PCB and must redesign it. Unfortunately, only the PCB was provided, no schematics or documentation. I know the PCB controls a VFD (which we have been given) and whilst I know we ...
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What ohm readings should be expected when testing the input terminals on a 3 speed blower motor that has been separated from all attachable wires

GENTEQ ECM 3.0 MOTOR WITH MODULE MODEL:5SME39SXL3019 1 PH 60/50 Hz 3/4HP 120/240 V 9.6/5.6 A 1050 RPM Cust. Model 51-102603-01 GC09
1 vote
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Why can I use an AC power supply to spin DC PC-fans?

This question might seem a bit alarming and it did come up because of an inadvertency on my part. I tried to reuse old PC fans for cooling and grabbed an old phone power supply that wasn't being used ...

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