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 \$ W = IR = I^2 * R = V^2/R \$
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1answer
45 views
How to calculate battery capacity required for home applications?
The issue I'm facing is calculating current draw from different household items. Like, if a fan is rated at 75 Watts, its current draw would be A = W/V so A = 75/220 and A = .34 amperes.
That doesn't ...
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3answers
67 views
Interpreting the power rating of the refrigerator [closed]
My refrigerator is rated as 130W of power. I need to know how to interpret this. Does that mean if the compressor works for a whole hour then only it consumes 130W? Or is 130W the average power ...
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2answers
71 views
Get current wattage from an electronics plugged in
Firstly, I'm not really an electrician or an electrical guy with lots of knowledge about electronics but I'm always interested learning to it.
Yesterday, I asked my wife to help me out determining ...
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4answers
99 views
Heating wire filament with low voltage / amps
Is it possible to heat either nichrome or copper wire (both 40 awg) with the following low-power delivery of 3.5 Volts, 7.4mW and 2.11mA?
This is very low power delivery and we're wondering if 3 ...
2
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3answers
112 views
Calculate wattage of incandescent bulb
I'm trying to find out the wattage of some bulbs supplied to a company I'm working for.
The product is a set of garden lights (Cheap Chinese) which is 10x small bulbs in parallel, powered by a 12Vac ...
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5answers
245 views
If watts is power and amps is current, what is volts
I know power is measured in the terms of watts, current is measured in amps, so is there an X for voltage?
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1answer
99 views
Kilowatt Hour Definition
This is a very simple question but something that I'm not able to wrap my head around. This Energy report states generated electricity. But what does "generated killowatthours" mean? I know that ...
34
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6answers
5k views
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 ...
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2answers
213 views
Combining Left and Right Hook Speaker Wires Into One Speaker
So I have an mp3 player, http://dx.com/p/94814, and the mp3 player comes with a left and right speaker output. For my equipment, I only have one speaker, not two. Can I just combine the left and right ...
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1answer
321 views
Mobile/Cell Phone Power consumption?
I'm trying to work out the amount of watts my mobile phone uses and thus how much power it needs to charge back to full power. My handset is the Nokia 820 Lumia and the specs are as follows:
Battery ...
0
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2answers
104 views
How do I find out power requirements from AC / DC specs?
I have a device with the following AC / DC specs:
100—240V, ~2 amps,50—60 Hz
24V DC @ 6.25 amps
click to see device
How to get power in Watts from this information?
Also, for a second device:
...
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1answer
232 views
Confusion between MW and MWh
A 1MW power plant producing power constantly for 24 hours will produce 24 MWh a day. Is that right?
If it is, I don't understand when it says, in ...
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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 ...
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4answers
103 views
Looking for a better understanding of a kilowatt hour and trying to size an electricity supplier using it
I am trying to design a fuel cell that can provide enough energy for 1 day's use a maximum capacity but I am having trouble sizing the fuel cell because I need a better understanding of kilowatt ...
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2answers
502 views
What is the formula for working out the volts, amps and watts of a DC Motor?
Can anyone remind of the correct way of working out the volts amps and watts on a DC motor?
I know it is something like:
\$ V=I \times R \$
\$ I=\dfrac{V}{R} \$
\$ W=\dfrac{V}{I} \$
or something ...
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2answers
172 views
High wattage speaker using low wattage amplifier [closed]
If I have a 250W amplifier and I want to use a set of speakers:
subwoofer x 1, 4 ohms x 1
mid-rage x 1, 4 ohms x 1
tweeters x 2, 8 ohms x 2
with a combined handeling wattage that surpasses 250W. ...
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2answers
342 views
Comparing A to Kwh, can it be done?
I have read this page: How to convert amps to kilowatts
I often purchase electricity from a supplier to power computing equipment within a data centre. Some sell me 10 amps, some sell me 2.16 kWh.
...
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2answers
478 views
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 ...
3
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2answers
945 views
Powering 10watt light bulb for 24 hours using solar power
I am a total noobi to solar power and even electricity so I appologies if I am asking a silly question.
Imagine I have a 10watt light bulb which I want to leave on for 24 hours a day. Will I just ...
4
votes
3answers
3k views
How to determine the best diameter for a cable?
In my understanding having a cable that has a too large diameter can lead to power dissipation, having one that is too small can lead to the same result.
apparently the second case is much more ...
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3answers
334 views
Plugging a 65W computer power plug into a 45W step down transformer [closed]
Is it safe? Would it only charge slower, or could it damage anything?
Here is the setup in more detail:
I'm in Europe, where plugs are 230V.
My computer was bought in the US, so it's a 110V ...
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votes
5answers
505 views
Cheapest way to dissipate energy (discharge battery)
What is the cheapest way to burn a lot of energy? Say I want to burn 800W (4V, 200A). How should I do that?
Ugly suggestions like: use a pot of water and a cable are welcome :)
It should be easy and ...
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1answer
301 views
Impedance for Helmholtz Coil Connected to Audio Amplifier
I am trying to design a Helmholtz coil, that will have an impedance of about 2 ohms (the reason for this being that I am going to hook it up to a audio power amplifier, so to get the same wattage ...
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1answer
428 views
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 ...
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3answers
299 views
How does electrical devices consume power?
I'm curious to know how does an electrical device can consume any amount of power it is required? Suppose the voltage here is 220V. How can you get any amount of electrical power say. 1000 watts out ...
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2answers
146 views
Calculating maximum wattage
If we get 220V from outlet, would it be possible to tell the maximum power (wattage)?
Since,
Power = Voltage (V) x Current (I)
Also, Is it possible to get the ...
11
votes
5answers
4k views
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 ...
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1answer
2k views
Converting Power/Watts in DC to Power/Watts in AC?
How can we convert Watts in DC to Watts in AC? for e.g A device needs 1A and 12V DC input i.e (1A x 12V = 12 Watts) 12 Watts DC. If we use an AC to DC adapter/converter to generate 1A,12V (12Watts) DC ...
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votes
2answers
345 views
How To Calculate Fluorescent To Incandescent Wattage? [closed]
This is simple mathematical question but I cannot figure it out:
Compact fluorescent lamps consume 75% less wattage and still deliver equal power of incandescent lamp. If 15W compact fluorescent lamp ...
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1answer
519 views
Audio: 2 Speakers * 200 Watt versus 1 Speaker * 400 Watt?
What is the difference between 1 speaker of 400 watt and 2 speakers of 200 watt? All the speakers are 12 inch.
Of course, I know the difference is mono/stereo. But I want to play in a little band ...
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1answer
91 views
Basic household energy consumtpion math
ok this is just for me to understand basic household economics.
let's say my electricity provider charges me 1 dollar for a kilowatt hour.
and let's say i have a device which claims to consume 100 ...
2
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1answer
120 views
How does a dual-wattage (automotive) bulb work?
I have a motorcycle headlamp bulb on my desk here. I notice the bulb has a rating of "60/55W" and has three connectors instead of the usual two.
Evidently these correspond to the high/low beam ...
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3answers
236 views
Negative effects of using underrated chargers
I was wondering what the effects of using a lower rating power rated supply for device would be. For example using a 1.52A supply at 19V to power a device where the charger that comes with the device ...
26
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1answer
1k views
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?
