Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [watts]

The unit of measurement and SI unit for power, named after James Watt. It is equivalent to energy flow per second or joules/second. In electrical terms: \$ P = I\cdot R = I^2 \cdot R = \frac{V^2}{R}\$

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What is the practical difference between watts and VA (volt-amps)?

I have seen one inverter rated at 300W, and another at 300VA. What is the practical difference between them, if any?
Thomas O
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Does turning a lighbulb on and off repeatedly use more energy than just leaving it on for hours?

Let's say I have a 60W bulb in a lamp in my bedroom. If I kept the lamp on for 2 hours straight but the next day, I switched it on and off 10 times in intervals of 5 minutes. Which scenario would use more energy?
Christopher Chipps
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What causes a fuse to blow, the current or the power?

Fuses and circuit breakers are often specified at a certain current they will 'blow'. Increasing the current will also increase the power. So if a fuse is rated for 12V DC and 20 A, this would be equal to 240 watts. If a different voltage is…
Jackson Harvey
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Why are batteries measured in ampere-hours but electricity usage measured in kilowatt-hours?

I was reading about energy usage in batteries and don't quite understand why it is measured in different units than home electrical usage. An ampere-hour does not include a measure of volts. But my understanding though is that a battery has a…
Alexis K
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Whats does "hr" mean among "V" and "Ah" in batteries?

I have a battery which indicates 12V25Ah/10hr. What does 10hr mean here? I guess "hr" stands for "hour". But 25Ah already means if battery is fully charged and if I load 12V 25A (=300W) to it, it should last for an hour (correct me if I am…
Farrukh
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Why is the power consumption of electrical lamps specified in kWh/1000h?

This is the box of a LED spot I just bought. I'm wondering why the power consumption is measured in kWh/1000h and not simply in Watts. Edit: The labeling standard can be found here. (Guide for the application of the commision regulation (EU) No.…
Lior Kogan
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What is the ⎓ symbol (which looks similar to an equals sign) called?

What is the ⎓ symbol called, which looks similar to an equals sign with the bottom line broken into 3 dashes, and is used in consumer electronics?
Boulab
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Multiple resistors in series instead of using a single resistor has any advantage: heat produced by the resistors of diffent watts are different?

I have two doubts, requesting you to answer my doubts separately. :) 1) I need a resistance of 'X', so is it better to use a single resistor of 'X' value or multiple resistance of r1+r2+r3='X'? What I mean is using multiple resistors in series…
Kiran
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Why is 10W resistor getting hot with only 6.5W running through it?

I am running about 6.5W though a 10W resistor. The ohm rating is 220 ohms, which is correct for the circuit ohms which is calculated to about 225 ohms. Here is what is running through my 220 ohm 10 watt resistor: 38.4 volts 0.17 amps 225.88…
hbsrnbnt
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Why is electricity consumption billed in watts and not amperes?

Basically the subject. Why would companies bill for wattage instead of amperes?
A. Munir
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Is it possible to step-up the output of a laptop USB port to 12 watts?

I've got a USB device that requires 12 watts to charge. My laptop appears to output less that that. My question is: Is it possible to step-up the output of a laptop USB port to 12 watts?
hawkeye
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What is the valid capacity ranges of Lithium Ion 18650 batteries?

I'm seeing wildly varying capacities that are seemingly fake on 18650 cells, such as these "9,800 mAh" ones on eBay, but are ~$1 / cell. However, 'genuine' cells from Panasonic and similar name brands seem to top out around 3,500 mAh or so, but cost…
Ehryk
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Watts - I think I'm getting free energy from a circuit?

Imagine I have a 10V battery with a capacity of 1Ahrs connected to a 100 Ohm resistor. I'll get 0.1A (V/R) at a power of 1W (current x voltage) for a total of 10hrs. As a watt is defined as J/s my battery produces 3,600J (1x60x60) in total. Now,…
user122374
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Wattage calculation for resistors in series

I need the formula for calculating resistor wattage when the resistors are in series. For example, say I have 3 1/4 watt 10 ohm resistors in series. What is the potential power dissipation for the entire circuit?
Matt Ruwe
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Why don't power meters measure volt-amps

When large inductive or capacitive loads are applied, the power meter will not indicate and bill you as the electricity gets lost in the lines. Why don't power companies just charge for this?
skyler
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