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Electrical Engineering
Electrical engineering is a field of engineering that deals with the study and application of electricity, electronics and electromagnetism.
23,056 Questions
What is maximum voltage for residential low voltage circuits?
The answer to this question depends entirely on where you live. All voltages quoted are 'nominal', or 'named', voltages and not the actual voltage as you would measure it with a voltmeter. National regulations stipulate how much these nominal voltages may vary.
For example, in the UK, the nominal voltage is 230 V, and the allowable variation is between -6% and +10%. So, the maximum (actual) allowable voltage is 253 V.
In some residences, e.g. Cyprus, a three-phase supply is common for residences, in which case the maximum nominal line-voltage is 400 V, with a nominal phase-voltageis 230 V.
What is the current carrying capacity of 1HP single phase induction motor?
The current varies but a rule of thumb is to allow 7 amps per horse power on 240 v, that means 7.64 amps on 220v, which 1.68 kVA.
1 horse-power is 746 watts, and with a conversion efficiency of 0.85 the power drawn is 880 watts on full load.
What produces a direct current?
The main source of direct current is the conversion of alternating current. Typically, AC is a sinusoidal waveform. Using what is called a full-wave rectifier, one can make all of the negative halves of the waveform positive. This means the waveform will have a series of humps in the positive region. This, however, is not usable DC yet; one must use a filter, or a series of filters, to smooth out the waveform until it is roughly linear and constant. The resultant signal is direct current. This is roughly what is contained within power adapters that you plug into your electronics from the AC wall outlet; they convert the AC signals to DC so the electronics can use the electricity.
There are many reasons for doing it this way. Mainly, though, AC power is easier to produce and more efficient to transmit over long distance. DC, however, is often more usable, so the AC is converted after transmission.
Another example of a DC source are solar panels, or photovoltaic cells, which produce electricity when hit by light.
Is surge current the same as short circuit current?
Not usually, but it may depend on the context. For instance, surge current might be used for a generator that is going to start a motor. Motors draw high current as they start, then the current drops to a normal level, called RLA, or running load amps. Generators have a watt rating for continuous operation called running watts, but they also have a 'surge' rating. You might see a generator listed as a '6000/5200 watt. The 6000 watts is the 'surge' rating. This means the generator can supply 6000 watts for a few seconds, such as might be needed to start a motor, but cannot supply more than 5200 watts continuously. Short circuit current on the other hand simply means how many amps will flow instantaneously if you drop a wrench across the two wires! For a normal utility power service, the short circuit current, also called fault current, can be several tens of thousands of amps, even though the main breaker is only a couple hundred amps.
What is a over current trip relay?
It is the one type of coil in the electrical motor starters. It is used to release the switch, i.e. turns off the motor, when heavy load is connected to the motor. It is used for the protection purpose.
What is the formula for calculating transformer voltage?
There are two kinds of transformers, autotransformers and isolation transformers. An autotransformer has one coil, an isolation transformer has at least two. To find the output voltage of a transformer, you need to know three things. First is the input voltage. Next are the number of turns on the primary coil, and last is the number of turns on the secondary coil. So! Our input voltage is going to be 120 in all three of the cases I'll give, and the number of turns on the primary coil will be 120--this makes the math easy, although you aren't restricted to putting 120 turns of wire in a 120v primary. You can put a million turns on if you want, and I've seen it. If our secondary has 12 turns, the output voltage will be 12--there is a 10:1 primary:secondary ratio. Normally this is called a "stepdown" transformer. It's used when the device requires less than line voltage to operate. A secondary with 120 turns will give a 120v output voltage. This is an "isolation" transformer. You use this as a safety device. Secondaries with 2500 turns give a 2500v output voltage--perfect for radio frequency amplifying tubes like the 4CX250A. For extra entertainment let's talk about the autotransformer for a minute. As I said above, this has one coil. It's tapped. If you've got 220v coming into a 220-turn coil and there's a tap at 110 turns, you're getting 110v out of it. Every soldier stationed in a country that uses 220v power buys one of these from the local post exchange so he can use the TV set he brought from home.
Why PM-MC meters can't be used for AC measurements?
It wont work for AC measurements. Not designed for AC application
How do you find current using ohm's law?
In the ohm's law formula we have, volts (V), amperes (A) and ohms (omega). There is no time in it. Scroll down to related links and look at "Ohm's law - calculator and formulas".
Can a 12vac coil be operated by 24vdc?
no, in an ac circuit the coil provides impedance but the DC coil needs some resistance to limit the current
How to change light bulbs in dashboard 1998 ford f150?
Step by step:
1. remove the piece that goes directly on top of the steering column.. this is held by clips, no screws
2. remove the one screw that holds the dash piece that goes BELOW the steering column.. this can now drop down by pulling it - the rest is clips.
3. remove the 3 screws that are visible that hold the dash piece that goes ABOVE the instrument panel. that piece is NOT ready to be pulled off yet!!
4. begin to carefully pull that dash piece that goes ABOVE the instrument panel out until you can access a spot where the headlight switch is coming out with the panel - there will be a plastic piece that you need to push in that acts like a clip - then the headlight switch can be removed and you will see the final screw that holds the panel in place - remove that screw.
5. once you have removed the above, you can access the 4 screws that hold the instrument panel in place - remove them.
6. carefully pull the instrument panel out. if you want to completely remove the instrument panel for easier access to the lights, you will need to first remove the transmission indicator ( P N D 2 1).. this can be achieved by looking along each side of it for the clips, pushing them in and sliding the piece down off the instrument panel.
7. pull the instrument panel outwards until you can access the wire harnesses.. push the clip in and pull them out (there are 3 harnesses for the instrument panel).
8. the instrument panel can now be completely removed and you will need to flip it over to see the back of the panel. the small white plastic pieces are all labeled on the PC board - ford even throws in some extra free bulbs if you don't have 4x4 (they install the bulbs the indicate your 4x4 status even if it will leave the factory without 4x4!).. the larger black ones are for the backlighting for the gauges - these must all be turned counter-clockwise to remove and clockwise to put back in.. they can be tough to get out and pliers can aid in turning them to remove.
9. follow the instructions in reverse to reassemble.
Can use 7.5mfd capacitor for a 5mfd capacitor?
Yes and no. 7.5 microfarads is close to 5 microfarads, so it might be possible to substitute. It depends on the particular circuit design requirements. If you are talking de-coupling or power supply usage, then you can probably substitute. If you are talking filter applications, such as a high pass filter, then you probably cannot substitute without changing the frequency response curve.
What is electrical excitability?
I think you mean 'excitation'; this refers to the process by which a current sets up a magnetic field which, in turn, induces a voltage into a conductor or coil -usually applied to transformers, motors, and generators.
What is ULN2003 integrated circuit?
as a buffer circuit... means whenever u need a high current....
e.x-> if u wnat to run a 12V relay using a PC parallel port(DB-25) output, u kan use such a TTL IC.... if u just connect the relay it will never switch!! the current in a parallel port output will just be enough to light 2 series LEDs....
ULN**** ICs are used in circuits that use PIC ICs(micro controller)..... Also ULN**** series ICs has low power dissipation...
-R-
What is the voltage across a 60.0 ohm resistor with a current of 3 13 amp?
V = IR
Voltage (V, measured in volts) = Current (I measured in amps) times Resistance (R, measured in Ohms)
Is your current 3.13? I'm not sure what you wrote there, but just multiply your current times your resistance.
Who invented the series and parallel combination of cells?
- Current travels in loops. In series you have one loop, or path for current to take. With parallel connections, there's at least two. This is why current divides in parallel and not in series.
- The usual problem here is to find the equivalent resistance, or capacitance. In the following formulae, R is the value of the equivalent resistance, while R1, R2, and R3 are the values of the...
- It can be used in the connection of emf..to have the greater current that we desired.so that it can produced a current.
What happens to the capacitive reactance when the frequency is doubled?
DATE: 17-MAY-12
THE CAPACITIVE REACTANCE VARIES INVERSELY WITH THE AMOUNT OF THE PRODUCT OF MAGNITUDE OF THE SUPPLY FREQUENCY, TWICE THE VALUE OF CONSTANT PI AND THE MAGNITUDE OF CAPACITANCE. IN OTHER WORDS, EVERY
TIME YOU INCREASE ANY OF THESE FACTORS OR IF SAY YOU FIX THE VALUE OF CAPACITANCE TO SAY 1 MICROFARAD AND OTHER FACTOR (i.e. 2 x PI) AS CONSTANT ALSO, BUT THEN WHEN DOUBLING THE FREQUENCY, SO THEN THE EFFECT TO THE CAPACITIVE REACTANCE WILL BE INVERSELY OR HALVED. THE MORE YOU INCREASE THE FREQUENCY, THE SMALLER THIS VALUE WILL BE. WHICH IN EFFECT ALLOWING MORE HIGH FREQUENCY CURRENT OR VOLTAGE TO PASS THRU THE CIRCUIT. AND THE REVERSE IS TRUE, MEANING ONCE YOU ALLOW LOW FREQUENCY CURRENT, THEN THE CAPAICTIVE REACTANCE WILL INCREASE AS A RESULT.
BY FMSJr. / ABU DHABI, UAE
Explain how load sharing is effective?
I want to install 4 sets of generator with synchronising system. During main goes off, the first set will start and the subsequent sets will start upon demand of load. Likewise, when load requirement goes lower, genrastor will start stop on the basis of demand.
What is the difference between a technician and electrician?
The technologists design, and draft the electrical network from the ground to each outlet. The technician and the artisan are the same. They install and repair the electricity in the building.
What is the difference between a square wave and a sine wave?
Inverter Tutorial and Frequently Asked Questions:
Q: What is an inverter?
A: An inverter takes DC power (battery or solar, for example) and converts it into AC "household" power for running electronic equipment and appliances.
Q: How is an inverter different than a UPS?
A: A UPS typically includes the battery and battery charger in one stand alone unit. However, there are UPSs that use external batteries, and PowerStream makes inverters with battery chargers, so the differences blurr as features proliferate.
UPSs also can have communication with the equipment that it is powering letting the equipment know that it is operating on standby, giving it shutdown warning, or communicating with the human in the loop. Inverters typically don't have this communication.
Q: Why are they called inverters?
A: Originally converters were large rotating electromechanical devices. Essentially they combined a synchronous ac motor with a commutator so that the commutator reversed its connections to the ac line exactly twice per cycle. The results is ac-in dc-out. If you invert the connections to a converter you put dc in and get ac out. Hence an inverter is an inverted converter. For more information about such converters see http:/www.nycsubway.org/tech/power/rotary.HTML (thanks to Karl W.Berger, PE for this answer).
Q: What if I want a DC output to run such things as a laptop from a car cigarette lighter, or telephone equipment at -48 volts?
A: Then you want a DC/DC converter. PowerStream has some DC/DC converters just for those purposes. http:/www.powerstream.com/dcdc.htm
Q: What is the difference between sine wave and modified sine wave?
A: Alternating current (AC) has a continuously varying voltage that swings from positive to negative. This has great advantages in power transmission over long distances. Power from your power company is carefully regulated to be a perfect sine wave, because that is what naturally comes out of a generator, and also because sine waves radiate the least amount of radio power during long distance transmission.
On the other hand, a sine wave is expensive to make in an inverter, and many sine wave techniques use heavy, inefficient transformers. The most inexpensive way to make AC is to switch the DC on and off--a square wave. A modified sine wave is scientifically designed to simulate a sine wave in the most important respects so that it will work for most appliances. It consists of a flat plateau of positive voltage, dropping abruptly to zero for a while, then dropping again to a flat plateau of negative voltage, back to zero for a while, then returning to the positive voltage. This pause at zero volts puts more power into the 60HZ fundamental than a simple square wave does, so it is called "modified sine wave" instead of "square wave."
Q: Can I use a modified sine wave inverter for my medical equipment?
A: For Medical equipment, oxygen generators, etc. talk to the manufacturer of the equipment. PowerStream inverters are never tested or rated with medical equipment, and we don't guarantee that they will work to save your life. For such applications please find inverters that are rated and tested for such applications.
Q: What about square wave inverters?
A: These old-fashioned inverters are the cheapest to make, but the hardest to use. They just flip the voltage from plus to minus creating a square waveform. They are not very efficient because the square wave has a lot of power in higher harmonics that cannot be used by many appliances. The modified sine wave is designed to minimize the power in the harmonics while still being cheap to make.
Q: How do I know if I need a sine wave, or if I can live with a modified sine wave?
A: The following gadgets work well with a modified sine wave: computers, motor-driven appliances, toasters, coffee makers, most stereos, ink jet printers, refrigerators, TVs, VCRs, many microwave ovens, etc.
Appliances that are known to have problems with the modified sine wave are some digital clocks, some battery chargers, light dimmers, some battery operated gadgets that recharge in an AC recepticle, some chargers for hand tools (Makita is known to have this problem). In the case of hand tools, the problem chargers usually have a warning label stating that dangerous voltages are present at the battery terminals when charging. We would like to add to this FAQ any appliances that you have had trouble with, or had success with, using modified sine wave inverters.
Q: Why do I hear buzzing on my stereo when using a modified sine wave inverter?
A: Some inexpensive stereos use power supplies that cannot eliminate common-mode noise. These would require a sine wave inverter to operate noise-free.
Q: Why don't I measure rated voltages when using a multimeter on my modified sine wave inverter?
A. The rated voltage is an RMS (root mean square--they square the value to make sure it is always positive, then average it, then take the square root of the average to make up for having squared it in the first place) measurement. Most multimeters are designed to give correct RMS readings when applied to sine waves, but not when they are applied to other waveforms. They will read from 2% to 20% low in voltage. Look for a voltmeter that braggs about "True RMS" readings.
Q: How should I select the right size inverter?
A: First add up the power ratings of all the appliances, then buy the next larger inverter! At least that is the simple answer. Note, however, that some appliances, such as table saws, refrigerators, and microwaves have a surge requirement. PowerStream inverters are designed to supply such surges, but since every appliance has its own requirements sometimes you will need to get a bigger inverter than you would otherwise think. Note that the inverter isn't the only consideration when you are pondering the mysteries of start up surges. The battery must also be able to supply the surge power, and the cables must be able to supply the increased current without dropping the voltage too much.
Q: How is a microwave rated for wattage?
A: When you buy a microwave oven you want to know how intense the microwave field is, not how much the oven draws from the wall. So a microwave oven that boasts 600 watts on the box, will have 1200 watts on the boilerplate in the back. Don't be fooled!
Q: Are stereo amplifiers rated the same way?
A: Stereo manufacturers are bigger liars than politicians. Some times they use peak output power (milliseconds), sometimes they use power drawn from the wall, but often they just look at the competition's carton front and add 10%. However the truth is available: look at the boilerplate sticker, which has been evaluated by UL.
Q: Why do I need such humongous cables to the battery when a small cord takes the AC output fine?
A: Power is volts times amps (Watts = V x A). So if you have a lot of voltage you don't need many amps. Roughly you need 12 times as much current from the 12 volt battery as you need from the 110 volt AC outlet. Current is what causes cables to heat up, not voltage. That is why they use thousands of volts in power transmission grids. The thing to do when you have lots of current is to lower the resistance of the cable. The larger the wire the lower the resistance. Think of the cable as a water pipe. A big pipe (wire) can carry more water (current or amperage) with less pressure (voltage), and will present less pressure (voltage) drop from one end of the pipe to the other.
Another consideration is how far the cable has to run from the battery to the inverter. Long cable runs are expensive, either in copper or efficiency, or both.
Q: Why would you use a 24 volt inverter instead of a 12 volt inverter?
A. At a given power rating a 24 volt inverter will need half the current as a 12 volt inverter. This makes the entire system more efficient, and since high current transistors are expensive, the inverter will be cheaper.
Q: Should I use aluminum wire, or must I use copper?
A: Aluminum is cheaper and lighter, but it also has higher resistance for a given gauge and is more difficult to connect to. If you are an expert in such things, or know one, and need the advantages that aluminum gives, go ahead. If not, why not use the best conductor, copper? (Silver is slightly better, but it is cheaper to use a larger diameter copper). To compare the two look at our web page http:/www.powerstream.com/Wire_Size.htm .
Make sure to use good insulation, 90°C rated or better. Also, running two sets of parallel wires instead of one can cut down on the wire heating due to more surface area.
Make sure to follow all applicable electrical codes. Inverters must be grounded properly, and treated with respect, since they put out potentially lethal voltage. A lot of smart people have worked for 100 years to develop rules which will keep you out of trouble if followed. These rules are called the national electrical code, and your friend the electrician has it memorized (or knows where to look it up).
Q: Should I use a laser printer with an inverter?
A: Only if you must. Laser printers use up a surprising amount of power (due to the heated rollers), and will discharge your battery faster than you expect, even on standby. If you do, make sure the inverter is rated for the power of the printer plus computer plus monitor. It doesn't do any good to have your computer brown out as soon as the the printer starts to print. Ink jet printers, on the other hand, use a surprsingly low amount of power.
Is high power factor good or bad to the power company or consumer?
The power required by the appliance is directly proportional to the current,voltage, power factor. If the power factor is low, more current is required to supply the rated power of the appliance hence the ohmic losses increase. Therefore the efficiency decreases and the voltage regulation increases which is bad for the power company as well as the consumer.
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In the study of alternating current [that which supplies our homes and businesses in the United States], it will be observed that there are alternating waves of both voltage and current.
In a circuit with purely resistance load, the waves of current and voltage are in exact phase relationship to each other. This means that when the voltage is at it's peak, the current flow is at it's peak as well.
An inductive load [coil] causes the current wave to lag or fall behind the voltage wave, so that the peak current flow is some time after the voltage wave is at it's peak level.
A capacitive load [capacitor] causes the current wave to lead or advance ahead of the voltage wave, so that the peak current flow is some time in advance of the peak of the voltage wave.
The consequence of this is that the AVAILABLE REAL POWER is the relationship between the current and voltage waves.
Resistive circuits have a power factor of 1.0, or unity, because the waves are in phase.
The more out of phase the relationship between voltage and current, the less efficient the use of available power, the more "waste" energy.
The less efficient the use of energy, the larger the size of transmission and generating equipment required to provide for energy needs, and the more costly the operation of utilization equipment.
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The power factor of a device is what determines how much useful power is used out of the total amount of power which is supplied to it from the source.
A power factor as close to 1 as possible is desirable because then most of the power transferred from the source to the load is useful power.
1. If a device has a power factor much less than 1, that means more total input current must be supplied for a given output power dissipation and a more powerful source is required to deliver the required output power. This means the device must draw a higher amount of volt-amps (VA) compared to the actual load power it is delivering, which means its conversion of input power VA to output power VA is inefficient.
2. The closer to a power factor of 1 that a device has, the better the total current which has to be supplied will match the output from the device, and the more efficient it will be in its conversion of input power VA to output power VA.
For more information see the Related Link shown below.
What is the purpose of using Pulse Width Modulation?
A; PWM is extensively used in PWM power supply whereby a fix frequency is setup but the duty cycle change to transfer power. Actually the maximum power is transferred during the rise and fall of the square wave
What is FLA in electrical terms?
FLA =
full load amps
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It is a term that is associated with motors. It is the amperage of the motor when it operates at its full rated horsepower under load.
What is relationships of capacitive reactance to resistance?
when ever current passing through any two parallel transmission line than due to the dieletric property of conductor some what capacitance effect will be generate between them that phenomina called as capitance reactance/////////////////// that symply we can called capitance reactance is measure of capitance
The reactance of a capacitor is its resistance.
