Questions tagged [power]

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22 votes
4 answers
4k views

How does turning off electric appliances save energy

We all know if we use less electricity we save energy. But the energy we're getting is result of burning (not necessarily the literal meaning) the fuel. Even if we don't use that energy that fuel is ...
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20 votes
5 answers
11k views

Why does it take so long to restart a nuclear power plant?

I have heard a couple of times that an operating nuclear power plant which was shut down (non-emergency; e.g. for a regular check) needs over 24 hours (up to 72 hours?) to get up running again. Why ...
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11 votes
1 answer
3k views

How to calculate Power of motor when used as a generator?

How can you calculate how much power can be generated by a motor when used as a generator (like a motor used in a wind turbine)? Does the power depend on how fast the magnet is rotated? If so, is ...
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10 votes
4 answers
19k views

Does a transformer use power when output isn't under load?

I was reading about how AC to DC converters work with a step-down transformer and then a diode bridge to convert the lower, stepped down AC voltage into DC. What I don't understand is since the input ...
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9 votes
1 answer
4k views

What is the difference between Bluetooth Low Energy and Bluetooth BR/EDR in Park mode?

It is known that Bluetooth Low Energy transmits data only during short time intervals called Connection Events. Connection events occur regullary with predefined period. The rest of the time Bluetooth ...
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8 votes
2 answers
4k views

Why do hydroelectric plants use turbines instead of an efficient 'water wheel' configuration?

I have been thinking about hydroelectric plants and I have been wondering why they are built the way they are. As in understand it, a stream of water is sprayed at a turbine, located at the bottom of ...
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  • 189
7 votes
1 answer
115 views

What needs to be considered when configuring the clock system for a MSP430F5xxx micro-controller?

I need to configure the clock systems for a MSP430F5528 microcontroller. The current development board has a 24MHZ crystal attach to XT2 pins (XT2IN/XT2OUT). The current design will need to support ...
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7 votes
1 answer
122 views

How to apply power flow analysis?

I have an (AC) power grid topology with generators, consumers, power lines, tranformers, etc. I also have a "snapshot" of the system's state, i.e., I know how much real power the generators feed, how ...
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  • 315
6 votes
2 answers
4k views

How can I calculate the temperature rise of a circuit board for a given power dissipation and area?

I have a PCB of approximately 4" x 4". It has a single long spiraling trace on it. The trace is 50 mil 4 oz copper, so nominally it's good for something like twenty amps before it overheats. But this ...
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6 votes
2 answers
256 views

Having three heaters on single PCB

I posted this question on electronics SE, but was suggested that I post it here. I basically having three heaters (serpentine pattern) on a PCB (fiberglass board), as the following image shows: The ...
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5 votes
3 answers
4k views

Relationship between wind velocity, turbine rotor diameter, and power output

I'm trying to understand and identify the equations to use in defining the relationship between wind velocity, turbine rotor diameter, and power output for a wind turbine. To simplify my question, ...
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5 votes
1 answer
56 views

How to select a micro controller for a low power applications?

I am interested in a microcontroller for a low power application. I have been advise to look at MSP430 or Microchip PIC microcontrollers. I also wonder if ARM-Cortex-M0 is a good choice too. At a ...
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5 votes
1 answer
2k views

Alcohol as a working fluid?

Alcohols with their lower boiling point and overall non-toxicity, could they be used as a turbine working fluid instead of steam water?
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5 votes
1 answer
1k views

Third Rail vs Overhead Cable: which is more efficient in terms of electricity consumption?

I'm well aware that there are many different factors to be considered, such as ease of installation/maintenance, conversion from AC to DC, environment, distance, speed, frequency of turns, and so ...
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  • 299
5 votes
1 answer
2k views

Mathematical expression for power loss in a dielectric

I am trying to prove the equation $$ \frac{\bar{P}}{V}=\frac{1}{2}E_0^2\sigma_{AC} $$ which can be rewritten as $$ \begin{align} \frac{\bar{P}}{V} &= \frac{1}{2}E_0^2\sigma_{AC}\\ &=\frac{...
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4 votes
2 answers
181 views

Do 3 blade wind turbines generate more power than a 9 blade, all else being equal?

After doing some research, I have come to the realization that 3 blade design horizontal turbines have the greatest maximum coefficient of performance. Most sources seem to agree a Cp of ~0.45 at TSR=...
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4 votes
1 answer
1k views

What's the history of the 345 kV voltage level in power transmission?

I'm interested in the history of the 345 kV power level for high voltage transmission in the United States. I've got two (and a half) questions: According to this source 345 kV was first applied in ...
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3 votes
2 answers
113 views

Intuitive explanation for why doubling max speed is proportional to eightfold power

I read that when you want to double the max speed of e.g. a boat you would have to increase the power eightfold! I could understand that you have to square it (= fourfold) because you are working ...
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3 votes
2 answers
157 views

Planned power outage and backup generator

In a few days, there will be a power outage that will probably last for 8 hours. We had this issue before, but then only our part of de building was affected. It was temporarily resolved by using 2 ...
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  • 131
3 votes
2 answers
282 views

Motor selection [closed]

I am trying to build a linear actuator for which I am trying to select a appropriate motor. I need to move about 1 kg of weight at about 1.2 m/s using a stepper motor. What specifications of the ...
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3 votes
1 answer
136 views

What is the difference between a diffuser and a duct in turbines?

I have been reading this paper, which addresses the advantages of diffusers in cross flow turbines. The abstract says (emphasis is mine): A CP’s extraordinary improving resulted when yaw increased ...
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3 votes
1 answer
747 views

CUF v/s PLF of power plants

What is the difference between capacity use factor (CUF) of solar power plant and plant load factor (PLF) of coal based power plant? Can we compare both since they seem analogous?
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3 votes
1 answer
170 views

Does electricity go through non-metal materials or not?

Ever since I was a little boy, I've always had this idea that electricity can only go through metal materials. For example, if I put a 100% metal screwdriver into the socket in the wall, I'm going to ...
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3 votes
1 answer
60 views

Power a microcontroler with a motorcontroller?

I have a motor controller that operates at 10-50V and draws 5A controlling a 3V motor that draws less than 1A. I had a an idea where I want to try to use a microcontroller to control this set up. The ...
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  • 331
3 votes
1 answer
54 views

Power formulae without phasors

I wanted to derive the formulae for active, reactive and apparent power. While I understand the concept of phasors, I think I would find an analytical proof that doesn't involve phasors, more ...
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3 votes
2 answers
127 views

Is it Possible to Generate Power From Sewage Sludge?

I have read about the application of sewage sludge incinerators1 but they do not have a net-positive power-generation. Is there a way to generate net-power from sewage sludge? What are the processes ...
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3 votes
0 answers
127 views

PMDC Motor Characteristic Graph

I am trying create a graph similar to as shown below. However, I am confused as to how the torque is related to the characteristics. The graph that is to be replicated for certain parameters: The ...
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3 votes
0 answers
41 views

Understanding transformer secondary winding

I purchased a step down transformer from a junk yard. I tested the transformer and it works but I am confused as to the secondary winding. The primary side has these markings G 0V 100V The secondary ...
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3 votes
1 answer
586 views

Basetech BT-305 missing resistor

I just modded my Basetech BT-305 laboratory power supply to become an IoT device. Everything works as planned, except the volt display in the multimeter-part of the supply, which is directly shown ...
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3 votes
0 answers
63 views

clockwork motor output in joules formula

I'm trying to understand the output of clockwork coils in joules or watts for different coils. You know the pullback car or windup pocket watch mechanism. I have heard it also called power in the ...
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  • 131
2 votes
2 answers
6k views

What is the difference between shaft power and brake power?

I know little about internal combustion engines and I feel a little confused about brake and shaft powers. I read a book that only talks about shaft power, and other that only talks about brake power, ...
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2 votes
1 answer
436 views

How much power does it take to supply a laser which delivers 100 watts? [closed]

To enable the functioning of a laser which delivers--on average--100 watts of energy in its beam, how much power does it take? (Does the 2nd law of thermodynamics dictate that the average power ...
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  • 141
2 votes
2 answers
224 views

Torque Problems vs Motor Problem?

I want to preface this by saying I am software engineer so each part of this robot build has been a lesson on its own. From welding, to CAD design, pillow block bearings, etc, etc.... I am working ...
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2 votes
3 answers
2k views

How to determine the compressor power in a refrigeration system?

The picture below represents a refrigeration unit In order to calculate the power produced by the motor, two quantities must be measured Angular speed of the motor. This parameter can be observed ...
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2 votes
1 answer
7k views

Specific energy vs Specific power in batteries

When looking at the Wikipedia page for Lithium-ion batteries, one can see that there are some technical details such as Specific Energy and Specific Power, but I don't know how to connect them. For ...
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  • 604
2 votes
1 answer
45 views

What happens if current provided to mono phase motor is less than rated power

I have a 0.5 kW single-phase AC motor. What happens if the supply is 220 V but can't supply the full current needed? Will the motor torque be lower? Or will it be slower? Will it be any ...
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2 votes
2 answers
2k views

How to estimate power consumption for an oven given volume?

Is there a good way to estimate the power consumption of an oven/heating device given the volume of the oven? I'm trying to do really, really dirty/quick math - I know that the average oven uses ...
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  • 23
2 votes
2 answers
89 views

Sun as water pump in underpressure water power circle

Introduction A water storage power plant pumps water up to a reservoir when there is more power available than needed and lets the water flow down when power is needed. For pumping water up, ...
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  • 125
2 votes
1 answer
24 views

AC Harmonics on a system appearing as DC

I have a theoretical question about harmonics and DC. Given I have a circuit which has a power supply providing an AC input(230Vrms @ 50Hz), this then goes into a load which, takes this supply ...
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2 votes
1 answer
36 views

What are the characteristics of a motor that will generate current and is powered by a 30 cc, 2-stroke small engine?

Problem: I am trying to hobby-build a generator using a (old, working, throw-away gas, yard blower) 30 cc, 2-stroke engine. The 2-stroke engine will spin a motor and I want the motor to generate DC ...
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2 votes
1 answer
17 views

Maximum amps from a switching voltage regulator

Looking at a part like this LM2596 It is rated for 3Amps with a voltage range from 3.3-12 volts. Does that mean that this voltage regulator will only output a maximum of 3amps?
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2 votes
1 answer
2k views

What kind of signal is the signum function? A power signal or an energy signal?

I'm studying "signals and systems". We can indentify two kinds of signals: power signal and energy signal. The definitions are: Energy of a time-continous signal $$ E_x = \int_{-\infty}^{+\infty}{|x(...
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2 votes
1 answer
35 views

Transformer Phase Fault

I have a transformer for troubleshooting. It is a 3 phase DELTA-WYE Step down (11KV/400V) transformer, the low side voltages (secondary) are Line to line voltages: RED-YELLOW : 400 V YELLOW - BLUE :...
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2 votes
4 answers
516 views

Measuring shaft torque of a small motor

I would like to determine the mechanical output torque and power of a small motor without using expensive strain guages and similar and have come up with the idea of determining the maximum mass that ...
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2 votes
2 answers
1k views

Calculate maximum acceleration of a car from rest (optimum launch)

First disclaimer: I have a background in math, but I'm no expert in engineering or physics. This is the first question I've ever posted and I think it belongs here, but please let me know if belongs ...
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2 votes
1 answer
97 views

Short power outage, deliberate?

The power went out in my block just now, so I got in my car and drove around and found a utility truck next to a pole that is at the junction between the block circuit and an adjoining circuit (which ...
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  • 1,615
2 votes
2 answers
91 views

how much power is needed to move a linear axis

Ι need help calculating the power usage for a linear axis motor. it must move up and down at a maximum speed of 0.5 m/s a load of 50 kg What I did so far: The load (i.e. weight) acting on the motor ...
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  • 23
2 votes
0 answers
50 views

Overcurrent protection, limit for nominal current or stall?

Background: I'm currently working on a robotics design that will drill through soil. I have selected a 48V motor who's nominal current is 3.17A and has a stall current of 42A. I will be driving the ...
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  • 331
2 votes
3 answers
89 views

Relation between armature voltage and mechanical power in electrical Engineering

I am searching for an effect chain that leads to the mechanical power $P_{mech}$ of a DC motor, starting with the applied armature voltage $U_{A}$. My request also includes all the electrotechnical ...
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  • 41
2 votes
0 answers
32 views

Why 'battery storage power stations' use mainly liion batteries?

As I understand liion batteries have lower lifetime, than LiFePO4. Why would such big stations use liion batteries then? Wouldn't replacement cost large amount of money? And how long those liion ...
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