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.
19
votes
6answers
687 views
How precise is the frequency of the AC electricity network?
If I make a digital clock which first detects the AC frequency roughly (whether it is 50, 60, 100Hz, etc), then uses it as its clock pulse source, how precise would it be? Would it work world wide ...
16
votes
1answer
3k views
How can I detect a power outage with a microcontroller?
I have the following power supply configuration:
AC MAINS -> UPS -> 24V POWER SUPPLY -> 5V VOLTAGE REGULATOR -> PCB (microcontroller).
What's the best solution to detect the power outage on the mains ...
15
votes
1answer
433 views
Does this device which claims to reduce reactive energy from a house work?
I've opened a device that states that it can reduce the reactive energy from a house, by plugin it directly to the power outlet/wall socket. I think it is a con, so I've opened it and I saw this black ...
14
votes
5answers
3k views
What exactly are harmonics and how do they “appear”?
From reading so many sources online, I still cannot grasp why a different waveforms have harmonics.
For example: when designing a silly amplitude modulation (AM) circuit that puts a square wave from ...
11
votes
4answers
5k views
Creepage distance for PCBs handling line voltage AC?
What is the required creepage (e.g. trace-to-trace) distance for PCBs handling 240VAC rms? What about 120VAC?
This is for UL and CE certification.
The standards for PCB Creepage (e.g. the distance ...
10
votes
4answers
375 views
Burnt AC Bulb Failover
I have a 60W, 120 VAC incandecent bulb used as a heater. Today it burned out and resulted in a water system freezing. I would like to be able to hook up a spare bulb that can come on if the first bulb ...
10
votes
7answers
603 views
NEMA 5-15P blade holes
Why do most NEMA 5-15P (North America 125V 15A) line and neutral blades have holes in them? I've been wondering this for quite some time and haven't yet found a satisfactory answer.
10
votes
1answer
210 views
Is this LED fixture safe for use with its current fabrication?
My father is currently interested in investing into a Ukrainian LED fixture manufacturer, and after he bought home a sample, I'm scared. There are 94 LEDs paired up with diodes, all in series, ...
9
votes
5answers
1k views
detecting zero cross in ac?
I need to detect zero crossing for a soft starter. A long while ago, I have done it using a 1 Mega ohm resistor directly connected to micro controller at one side and live power at another side. I was ...
9
votes
3answers
1k views
Can you put a 120vac positive line into a breadboard?
Is there anything I need to know about putting a 120vac positive line in my breadboard? (Like, for example, if it's a bad idea to do that to begin with.) It will just be a christmas lights strand at ...
9
votes
4answers
591 views
Why are some AC outlets and plugs polarized?
This will show my naivety when it comes to alternating current... but why are some plugs and sockets on AC outlets polarized (one prong is taller than the other)?
(See this question on DIY.) (Or this ...
9
votes
5answers
2k 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, ...
9
votes
2answers
2k views
How do the tiny AC->USB power supplies work?
The iPhone and Kindle both come with tiny power supplies that take in 120v AC and output around 5V at 0.85 to 1 amp. They seem to be too small and light to have a transformer, and generate very little ...
9
votes
2answers
3k views
How do I select the accompanying components for an optocoupler?
I'm using an optocoupler (MOC3021) to sense the On/Off state of an electrial appliance using a microcontroller ATmega16L. How do i go about doing this? My mains supply specs are 230V, 50Hz. How do I ...
8
votes
7answers
772 views
how can I make a large transformer less loud?
I have a large 2600W 230V -> 28V transformer, and it makes a constant quite loud bzzzzzz sound while it works. Is there any way to make it more silent (other then buying an equivalent SMPS which I ...
8
votes
5answers
580 views
Why do AC-to-DC adapters have long cables on both ends?
Why do AC adapters have long cable on both ends? I believe that almost everyone using one would want it either directly next to the gadget it is powering (even possibly joined together with it if ...
8
votes
4answers
378 views
Is there a device that converts any AC frequency to 60 hz?
If I have something like a windmill generator that generates AC current, but at variable frequency, what device(s) would I need to convert that variable frequency into a constant 60hz frequency, so ...
7
votes
4answers
392 views
Does appliance wattage differ by country, since the voltage does?
As an example, I have an AC-DC "wall wart" that specifies an input voltage of 100-230 volts and an input current of 0.3 amps. Since my mains supply is 230v:
Does that mean that it uses 230*0.3=69 ...
6
votes
8answers
745 views
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 ...
6
votes
3answers
2k views
Why is high voltage AC more common than high voltage DC?
Why is that high voltage AC is more commonly found than High voltage DC? Example my battery powered fly swatter and fluorescent lamp both use high voltage AC. Why can't these devices increase the DC ...
6
votes
6answers
6k views
How electrons inside copper wire behave when source is ac or dc?
When a simple copper wire is connected to AC or DC, what actually happens to the electrons inside the wire?
I.e. What kind of path do they follow when they reach the end of the wire? If anyone can ...
6
votes
2answers
1k views
Transformer labeled 120v-60hz-35va-12v - What exactly does it do?
I have a pool light whose bulb physically broke, but I've found a way to open the water-tight bulb enclosure to get at the actual bulb. I'm trying to either hunt down a replacement bulb (rather than ...
6
votes
2answers
417 views
What keeps mains power at 60hz?
In a power plant, what keeps the power at a solid 60hz? It seems like turbines can't always be running at the exact same speeds, given that combustion doesn't always give the exact same temperature ...
6
votes
3answers
2k views
Control 220V AC line using MCU
I want to switch ON and OFF an incandescent bulb using MCU. Please suggest an electric switch (like relay or something) for 220V 50Hz AC line which can be used here. I would prefer something very ...
6
votes
1answer
2k views
what will happen if i apply 220 dc voltage to 220 ac system (load) like lamp?
Please help me. Let say if I have a lamp which is operated on 220 V ac. Instead of applying 220 AC voltage I apply 220 DC voltage then what will happen? And if i want to convert this 220V dc to 220V ...
6
votes
3answers
193 views
What difference does it make to an appliance whether the supply is sinusoidal, or any other shape?
Just what the title states.
I understand some appliance/s may be damaged if the supply is any shape other than sinusoidal. E.g. sawtooth, square ...
Why is this the case? How does the shape of the ...
6
votes
1answer
739 views
Current limiting at mains voltage
I am driving a BTB16-600BW triac using a MOC3052 exactly as suggested in the MOC3052 datasheet:
The current into the power triac gate is limited using the highlighted resistor. My triac requires at ...
6
votes
4answers
370 views
Validate Triac circuit
I'm designing a device to switch a heating device driven by mains power. I've done quite a lot of research and realize there's a lot of information out there but as i'm dealing with potentially deadly ...
5
votes
3answers
308 views
High frequency mains transmission
Someone told me that if we used something like 1 kHz AC instead of 50 or 60 Hz AC, it would end up being much cheaper and efficient, because we could use smaller transformers. Is this true? It seems ...
5
votes
2answers
148 views
What is the difference between VA and W for a relay
I am trying to choose a relay to control a compressor.
The compressor alimentation is 230V (50Hz), the max intensity is 0.9A and the power needed is 130W.
Then i found two relays: the ALD112W and ...
5
votes
4answers
443 views
I want to build a DC powered computer, what are the gotchas, where are the parts?
Google builds its servers with a Battery in the box so that they don't need a UPS. I'm wanting to do the same, but I'm wondering what all the gotchas might be for doing this, and where I'll find the ...
5
votes
3answers
863 views
How does DC transmission require several times less wire than AC?
In this YouTube video (scrolled to 5:55) there's a claim that replacing an AC high voltage transmission line with a high voltage DC transmission line allows for having seven times fewer powerlines ...
5
votes
2answers
410 views
How does an inverter affect the computer?
I have rampant power failure in my country. So to mitigate, we have an inverter that basically converts the charge from a big lead-acid battery to AC. But as far as i know this doesn't produce pure ...
5
votes
4answers
1k views
Why isn't it dangerous to put finger in light socket?
This is in reference to "Why three prongs?".
Why does this hold true: "Curious kids might still stick their finger in a light socket and receive a shock, but the unwanted current was directed through ...
5
votes
3answers
2k views
2 Phase to 3 Phase conversion
I have seen some boxes (with some capacitor circuits inside) which do 2 Phase PS to 3 Phase PS conversion. The problem was the motor gets heated up, exact 120 degree was not acheived. (only 90 ...
5
votes
3answers
1k views
Combining multiple AC/DC adapters
Many of us have lots of devices that uses AC mains (110V/220V) to DC (typically 12VDC) adapters. There's my LED table lamp, my Wi-Fi router, my Gigabit switch, my powered USB hub,.....
Such AC/DC ...
5
votes
2answers
2k 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 ...
5
votes
3answers
963 views
How can the capacitor be connected in reverse polarity?
If the polarity changes every time the AC switches, then why doesn't the capacitor explode?
5
votes
7answers
1k 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 ...
5
votes
4answers
297 views
First mains-powered project - best practices?
I'm about to commence building a project that's basically a USB-controlled dimmer. I think the main components will be:
Velleman K8064 voltage-controlled dimmer
Phidget 1018 usb interface board
...
5
votes
1answer
159 views
What is the Thévenin equivalent of the mains power supply?
Thévenin's theorem says that any voltage source can be modeled as an ideal source in series with some complex impedance. How does one quantify this model for AC mains supplies? What parameters are ...
4
votes
4answers
1k views
Can a 2-prong AC/DC converter switch polarity based on inverting the plug?
I got an electrical engineering degree 15 years ago that I barely use. Although I bought a fairly fancy multimeter, I will freely admit to having only a vague recollection of what I did back then... ...
4
votes
2answers
271 views
Will a 3 phase induction generator fight its own rotation?
So in a 3 phase induction generator with coils for the stator and magnets for on the rotor, I am wondering if the the current induced in the coils would create a magnetic field that would oppose the ...
4
votes
2answers
352 views
Actuator can use either 24V DC or 24V AC. What should I chose?
I will be using a damper actuator which can have either a AC or DC power supply. I do not have any strong preference for either, so what would you recommend? I assume that transforming 230V AC to 24V ...
4
votes
3answers
798 views
Why is power supply from electrical utility referenced to earth?
In response to the question Basic Training for working with 120V AC zebonaut had replied that "A regular wall outlet is referenced to earth" and this provides the close loop for the circuit to ...
4
votes
3answers
654 views
High power three phase ac motor controller
I have come across this question a lot in the design of a special 3 phase motor controller I plan to build this summer and I think I need to ask it directly to solve it.
I need to be able to ...
4
votes
3answers
171 views
Driving Permanent Magnet DC Motor via PWM
SUMMARY:
I am currently trying to finish up a DIY project I've been working on for a while: Building an electric potters wheel. I acquired a treadmill and salvaged quite a few good parts from it, and ...
4
votes
2answers
529 views
Can we remove the neutral wire?
If we have the connection shown below (star connection of the secondary part of a TX), the load per each phase is equivalent (balanced load), then the vector sum of ...
4
votes
1answer
672 views
DC power supply simulation trouble
I'm trying to simulate a relatively simple AC->DC power supply in LTSpice, but it's not quite cooperating with me. I've followed this schematic:
only replacing potentiometers with resistors due to ...
4
votes
1answer
528 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 ...
