Why DC current is not used in Homes?
Why DC current is not used in Homes as it is more safer than AC current.
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There are two important factors that determine the use of AC instead of DC:
1) Power: Power is defined by the voltage x current (V x I = W). This equation indicates that the higher the voltage, the lower the current, and that the lower the voltage, the greater the current, for the same power (consumption). If using a very high current, the thickness of larger diameter wire must, therefore more expensive. The transmission lines would be very expensive, so high voltages are used (thousands of volts) to transmit from the generating plants, with relatively thin wires.
2) Transformers: These work only with AC power (for induction), and are necessary to lower the voltage and current to raise the nominal levels used in homes.
Both factors are complementary, DC cables using low voltages, it would be too expensive (cable diameter should be large), as could not be used transformers.
In the case of using their own sources of energy such as solar, wind, chemistry, etc.. The use of AC would only be for reasons of standards, and this is solved by voltage inverters (DC to AC),
1) Power: Power is defined by the voltage x current (V x I = W). This equation indicates that the higher the voltage, the lower the current, and that the lower the voltage, the greater the current, for the same power (consumption). If using a very high current, the thickness of larger diameter wire must, therefore more expensive. The transmission lines would be very expensive, so high voltages are used (thousands of volts) to transmit from the generating plants, with relatively thin wires.
2) Transformers: These work only with AC power (for induction), and are necessary to lower the voltage and current to raise the nominal levels used in homes.
Both factors are complementary, DC cables using low voltages, it would be too expensive (cable diameter should be large), as could not be used transformers.
In the case of using their own sources of energy such as solar, wind, chemistry, etc.. The use of AC would only be for reasons of standards, and this is solved by voltage inverters (DC to AC),
+1
The reason we use AC current in our homes is because AC can travel longer distances over the electrical grid (sometimes called stepping up the current)and the current changes polarity by cycles. Although DC could be used, it would require more infrastructure to provide electricity to every home. Also the current in the neutral wire would have to return to the generating station. The use of AC over DC was settled during the War of Currents between the American entrepreneurs Thomas Alva Edison and George Westinghouse. Nikola Tesla was in favor of using AC and he disagreed with Edison about the use of DC current. Tesla resigned working for Edison and later worked for Westinghouse. AC current prevailed and that is why most homes use AC current today.
The reason we use AC current in our homes is because AC can travel longer distances over the electrical grid (sometimes called stepping up the current)and the current changes polarity by cycles. Although DC could be used, it would require more infrastructure to provide electricity to every home. Also the current in the neutral wire would have to return to the generating station. The use of AC over DC was settled during the War of Currents between the American entrepreneurs Thomas Alva Edison and George Westinghouse. Nikola Tesla was in favor of using AC and he disagreed with Edison about the use of DC current. Tesla resigned working for Edison and later worked for Westinghouse. AC current prevailed and that is why most homes use AC current today.
I remember that Tramcars in Calcutta used to run on DC.
Does Electric Train run on DC? Or Diesel Train Engines run on DC as it has its own Generators.
It seems that Heavy Machinery run on DC.
Does Electric Train run on DC? Or Diesel Train Engines run on DC as it has its own Generators.
It seems that Heavy Machinery run on DC.
The speed of an AC motor is closely tied to the AC frequency, hence they are very poor for variable-speed like trams/trains.
There are modern trains that do use AC motors (because they are more efficient), they use big-silicon to produce the output AC via DC, from probably 25KV AC.
L
There are modern trains that do use AC motors (because they are more efficient), they use big-silicon to produce the output AC via DC, from probably 25KV AC.
L
No, it's not.
This is what Edison used to say about the Westinghouse system.
L
This is what Edison used to say about the Westinghouse system.
L
Just to add to what everybody else has said, -- DC works for transmitting data, both analog and digital. That is why your phone lines are DC. But AC works for transmitting power more efficiently. I think the reason for much of the home power stuff being 12 volt DC is that it is somewhat safer, BUT only AS 12 Volt. But you need a lot heavier cables to handle high amperage with 12 volt and thick copper wire is expensive. Its a lot cheaper and more efficient to use less wire with more insulation. I helped to set up a little wind generator and we had to pay a lot for the heavy cable that was needed, way more than it would have been for just regular house wire. The fact is they probably should be making those with 120 volt outputs, except that when you couple them up to storage batteries the batteries are all 12 volt based. What is really missing in this beginning industry is a set of standards that everybody will go with. Then the cost of all the stuff will come down and putting it all together to work correctly will become much simpler.
And yes, as the others brought out DC starts a lot more fires because people don't realize they need really heavy gauge cables to handle the amperage.
And yes, as the others brought out DC starts a lot more fires because people don't realize they need really heavy gauge cables to handle the amperage.
Jan 4, 2012. 4:20 PMBurf
says:
I don't know what makes you think DC is safer than AC; at normal household currents, either one will kill or injure just as easily as the other.
The myth that DC is safer than AC began when Thomas Edison (the patent holder for DC power generation systems) was attempting to discredit Westinghouse's AC system from being adopted as the model for municipal electric power.
The myth that DC is safer than AC began when Thomas Edison (the patent holder for DC power generation systems) was attempting to discredit Westinghouse's AC system from being adopted as the model for municipal electric power.
IIRC, the myth was debunked using the electric chair - convicts had a far greater chance of surviving electrocution by AC than DC.
Of course, I may just be recalling another myth...
Of course, I may just be recalling another myth...
It is very difficult for me to select the best answer because again I am hearing that DC is going to come back in Homes.
Dipankar, when I was very young (4 years old), 1949) in my village was an old DC power plant, 220 volts. It was very noticeable the voltage drop proportional to the distance to the plant. Nearby, lights bright normally, but at 6 or 7 blocks were dim. The motors was often burned as a result.
Its only "coming back" for very, very special, off grid applications. Like I said, you won't see it used in general because using AC is much more sensible, and safer.
Power = current x voltage, but wasted energy = current^2 x resistance - so the higher the voltage, the less you waste in your wires - or the lower the chance of a fire.
In the USA for example, electrical fires are MUCH more common, because they use 110V supplies than in the rest of the 220V using world - for a given power, we need 1/2 the current.
If we used 12V supplies routinely - AC or DC, I hate to think what the fire stats would look like.
Steve
Power = current x voltage, but wasted energy = current^2 x resistance - so the higher the voltage, the less you waste in your wires - or the lower the chance of a fire.
In the USA for example, electrical fires are MUCH more common, because they use 110V supplies than in the rest of the 220V using world - for a given power, we need 1/2 the current.
If we used 12V supplies routinely - AC or DC, I hate to think what the fire stats would look like.
Steve
I remember when I was about 9 years old, we had DC in our homes and then around the year 1955 they started converting the home current to AC. I think at that time Calcutta City had its own Generating Unit. That is why I was curious to know when we had DC in our home why was it converted to AC.
In ultra-large systems, AC is converted into HIGH VOLTAGE DC for transmission, and chopped up at the other end. This prevents energy loss by radiation and eddycurrent and dielectric losses too.
DC is considerable MORE dangerous than AC, because it can cause muscles to spasm, and make you grip a live conductor harder. AC will "release" you 50 x a second.....
Low voltage DC in the home would cause all sorts of issues with fire and line losses.
Steve
DC is considerable MORE dangerous than AC, because it can cause muscles to spasm, and make you grip a live conductor harder. AC will "release" you 50 x a second.....
Low voltage DC in the home would cause all sorts of issues with fire and line losses.
Steve
Jan 4, 2012. 6:07 PMRe-design
says:
I've read about this over the years. The numbers may be off, I'm just going from memory but the point if valid.
DC is hard to step down without losses. With AC you can use transformers. When you generate DC you can only transmit it 20 to 30 miles before the resistance of the wire starts to degrade it too much. You start out with 120 volts and at the end you only have 70 or 80. With AC you start out with 15,000 and even after several hundred miles you still have 14,500 volts. Using transformers along the way you convert the high voltage to 120 volts ac. so you can build generating stations far apart rather than every 50 miles or so.
In the beginning there wasn't an easy way to convert dc to ac as there is now. So the losses would be much more than they are today.
DC current is as dangerous as AC. There are some situations where ac may cause more damage but you can die from getting your self across a battery such as from a Prius (700 volts).
DC is hard to step down without losses. With AC you can use transformers. When you generate DC you can only transmit it 20 to 30 miles before the resistance of the wire starts to degrade it too much. You start out with 120 volts and at the end you only have 70 or 80. With AC you start out with 15,000 and even after several hundred miles you still have 14,500 volts. Using transformers along the way you convert the high voltage to 120 volts ac. so you can build generating stations far apart rather than every 50 miles or so.
In the beginning there wasn't an easy way to convert dc to ac as there is now. So the losses would be much more than they are today.
DC current is as dangerous as AC. There are some situations where ac may cause more damage but you can die from getting your self across a battery such as from a Prius (700 volts).
Jan 4, 2012. 5:40 PMframistan
says:
DC is making a comeback in homes using solar cells and wind power. Some of those solar-powered homes use 12 volts and power things directly rather than converting up to 120 volts to power many items. There are many appliances that are made for camping and RV'ing that work on 12 volts so it makes sense to use DC.
DC also tends to generate A LOT more heat. When DC was being used fires were common, and power lines would fall frequently. That's actually where the then, Brooklyn Dodgers got their name, dodging falling or fallen power lines. Even Edison admitted before he died, that Tesla was right, and AC was the way to go.
No, I'm sorry. The Brooklyn Dodgers derived their name from "Trolley Dodgers":
(see Wikipedia, and the primary source citations therein).
New Yorkers ... routinely called anyone from Brooklyn a "trolley dodger", due to the vast network of street car lines criss-crossing the borough as people dodged trains to cross the streets.
(see Wikipedia, and the primary source citations therein).
DC is no safer than AC. The problem is that most real devices need a substantial amount of power, and both current and voltage (the product of which is power) can be fatal.
As has already been noted, the electrical distribution grid needs to be consistent. Since Edison lost the war with Westinghouse, the grid is AC, not DC.
As has already been noted, the electrical distribution grid needs to be consistent. Since Edison lost the war with Westinghouse, the grid is AC, not DC.
Jan 4, 2012. 3:51 PMaelias36
says:
Transformers only work with AC, so it's easier to use AC in the whole power grid.
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