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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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2
votes
2answers
3k views

How to use Gas Discharge Tubes, Transils and other goodies together

I would like to make a good surge protector for a device that will have a hardwired mains connection. The protected electronics will consist of a ~10W SMPS and a low-power AC load (<100W) ...
4
votes
5answers
388 views

Is direct current really better for pumped-storage hydroelectricity facilities?

Currently the article equivalent to War of the Currents in Russian Wikipedia section says that direct current is beneficial to pumped-storage hydroelectricity plants and provides no reference to that ...
4
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2answers
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?
4
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6answers
7k 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 ...
2
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3answers
4k views

Is this a good “pure” sine wave inverter design?

I'm in the initial stages of designing a pure sine wave inverter. My design is as follows: Wien Bridge Oscillator (5V at 50 Hz) -> Class D Amplifier -> Output transformer My question is, is this a ...
31
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3answers
14k 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 ...
13
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5answers
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, ...
7
votes
3answers
2k 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 ...
6
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3answers
9k 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 ...
3
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4answers
30k views

What happens if an AC voltage is applied to a battery?

Today I was checking the voltage between charging terminals going to the battery of emergency lantern using a multimeter. The multimeter showed a DC voltage of 9V and an AC voltage of 4V. Could ...
5
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4answers
476 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 ...
22
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8answers
25k 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 ...
4
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3answers
2k 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 ...
5
votes
2answers
4k views

Actuator can use either 24V DC or 24V AC. Which should I choose?

I will be using a damper actuator which can have either an 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 ...
7
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1answer
3k views

Using a triac to switch on/off a single phase AC motor

I want to use a triac controlled by a suitable optoisolator such as a MOC3020 to switch a single phase AC motor on and off, like the ones you'd find in a typical desk fan or a blender or similar. I ...
11
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3answers
8k 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 ...
9
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1answer
6k 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 ...
10
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9answers
6k 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 don'...
2
votes
1answer
574 views

Common mode Choke for AC voltage measurement

I'm trying to measure Mains AC voltage of 230V RMS/50Hz with the ADC of a MCU. Therefore I need some isolation and voltage division (+/-325Vp down to +/- 1V). The voltage division is easy to solve, ...
26
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7answers
4k 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.
3
votes
1answer
3k views

220v AC Fan regulator

i need to regulate the speed of a noisy kitchen FAN from a microcontroller (arduino board), i have been looking around and checked a lot of websites and schematics, and i think the solution should ...
1
vote
5answers
345 views

Crude/inexpensive AC to DC transformer

I am working on a circuit that is completly powered by 5VDC from a USB port. The circuit uses SSR's to turn on and off 120VAC from a standard wall plug; the 120VAC powers a high-power heater of sorts. ...
7
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8answers
2k 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 ...
5
votes
4answers
11k views

120VAC 60Hz Zero Cross Detector

I'm designing a digital phase-controlled light dimmer, and I need a zero-crossing detector circuit. From what I've read, it's a bad idea to wire the AC main directly to the microcontroller through a ...
5
votes
4answers
3k 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... ...
5
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3answers
1k 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 ...
7
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2answers
43k views

How are LED Christmas Lights Wired?

I'm planning on building some dimmable lighting controller for Christmas lights, but with LEDs being all the rage nowadays, I was thinking that instead of using triacs and dimming at 60/120 Hz, ...
14
votes
5answers
5k 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 ...
3
votes
4answers
14k views

Controlling water pump speed

How can you control the speed of an AC water pump? In particular this one. My guess is that PWM won't work on an AC motor? I've heard that controlling the voltage will change it's speed...is this ...
4
votes
2answers
3k views

Measuring VPP and DC offset of a 1Hz - 1MHz signal using MCU

I need to measure the peak to peak voltage and DC offset of a 1Hz to 1MHz sine/triangle wave. The signals amplitude varies between 0 and 2Vpp and the offset can vary between -2v and +5v. I will be ...
1
vote
1answer
2k views

Measuring Voltage of Unknown Type

My circuit is almost identical to the Wikipedia but with 5V in, 1pF cap, 4 pieces of IN4004 diodes. I am not certain whether it is AC or DC here and there (actually I do but not want to break my ...