Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [power]

Electric power is the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt (one joule per second). Use this tag where power is a primary concern for the design under discussion. Use the "low-power" tag when that applies.

Power is the rate of energy consumption, transfer, or storage. In general, power can be divided into real (or active) power and reactive power. Real power measures energy that is used to do useful work or lost as heat. Reactive power measures energy that is temporarily stored, generally in capacitance and inductance, before being returned to the grid. The combination of the two is complex power.

Reactive power is generally considered undesirable, as it is not used for useful work, but increases the design requirement of the transmission system.

Units of real power are watts (joules per second). Units of reactive power are VARs (volt-amp reactive). Units of complex power are VA (volt-amps).

See for questions on converting power.

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How much of a GPU's electrical usage is probably turned into a increase in air temperature?

I am trying to find a good rough guesstimate of how much of the maximum wattage usage of a graphics card is turned into hot air. Say a graphics card is rated at using X watts at maximum usage. How much of that is released as heat into the air via…
KDecker
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What happens when a device draws more current than the power supply can provide?

I am more of a software programmer, but I have a basic question on electronics. What happens when a device draws more current than the power supply can provide? And under what circumstance can it happen - bad board design or not determining the…
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Why don't we measure electrical consumption in joules, instead of kWh?

Why don't we measure electrical consumption in joules, instead of kWh? Aren't they the same measurements, but one is more "proper"?
Thomas O
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What do these two PNP transistors do in this power circuit?

I am a beginner in circuit design and I have been trying to understand the purpose of the Q2A and Q2B transistors in the above power circuit. Here is what I am able to understand so far. There are two power sources, +5V and +5V_USB. When +5V is…
adnan
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Are watts usually measured in watt-hours?

Pardon me, I'm a total newb to electronics. My question is, when a device is measured in watts, such as a 60-watt light bulb, is this ALWAYS supposed to be assumed to be watt-hours, i.e. 60 watts per hour?
stimpy77
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S = VI*/2 derivation

I was wondering Where I could find the derivation for the complex power formula, S=VI*/2, where S, V and I are complex phasors. I've seen a whole bunch of verifications where people sub stuff into the equation to show that it happens to work. Here's…
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Can you harvest electrical energy from the air?

I found a website recently about harvesting energy from the air, and I am wondering if someone could tell me why the following wouldn't work? Their "generator" is supposed to make electricity from the ionosphere (not UV, X-Ray, etc). Some claim it…
Arlen Beiler
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What is the correct spelling/capitalization of watt hour?

In some documentation I have commented that a field contains "the forward active power, in Wh". Which way should it be written (when I don't want to use the abbreviation)? the forward active power, in watt hours the forward active power, in Watt…
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Understanding electrical consumption

I have problems understanding the difference between electrical power and consumption. Can you help me understand what electrical energy consumption is? Let's say that I have a bulb, on which is written 100 W. How much does this bulb consume in 1…
ctp
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AC and DC devices

Why do home appliances like a light, TV, and fan use AC power directly from the supply, but a phone and laptop use an adapter to convert AC to DC?
user173707
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Does it make sense to use MWh/h as unit of measure?

Since MW is actually the rate of energy is being used, why would we use MWh/h as in Fingrid's electricity market Load and Generation forecast page? Wouldn't MWh/h be the same as MW???
L. Holanda
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How is the power factor part involved in wattmeter reading?

In a wattmeter, the current coil helps in measuring current and the potential coil is used for measuring voltage... but the real power that the wattmeter measures is \$V \times I \times \cos(\phi)\$. How is the power factor involved in the…
Yash Kumar
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What exactly is reactive power, in concrete terms?

I've been googling it for hours and frustratingly all I could find are vague hand-waving explanations. I get that \$\textbf{S}=\textbf{VI}^\textbf{*}\$ is useful because \$Re(\textbf{S})= P_{avg}\$, which is the average power used by the load. But…
Venuce
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Can I use a 3 pin kettle power lead instead of a 2 pin kettle power lead

I have a computer appliance that only accepts a 2-pin kettle power cord (UK plug type). I don't have a 2-pin available at the moment; only a 3-pin. The third pin that is missing is the ground connection. Would it be ok for me to use the 3-pin…
Ash2204
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ABCD to scattering parameters derivation

I'm currently studying microwave engineering as a subject. Everywhere on the internet and the books, they've only shown the derivation of S11 and S22 from ABCD parameters of a network. Yes, that's intuitive, since S11 is tau(in) and S22 is tau(out),…
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