Instructables

Why DC current is not used in Homes?

Why DC current is not used in Homes as it is more safer than AC current.

DrakerDG2 years ago
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
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.
Stepping DOWN the current, stepping UP the voltage.
Right! Thank you. I am still on your side!
lstookey1 year ago
My experience with DC power: I am a telecommunications engineer building central offices for some of the largest telcos in the world. In other words, I know what I'm talking about. Everything we have runs on DC. We don't do AC. I manage multiple DC plants with well over a thousand AMPs worth of juice.

DC power is not more dangerous than AC. Quite to the contrary, if handled correctly it is much safer. We have what we call breaker distribution frames. This is where multiple DC feeds terminate into what really is the equivalent of a "DC breaker box" in a rack if you think of the AC world. It's 7' tall and loaded with breakers. You can reach into the back of those, grab the copper bus bars and if you are not wearing metal, come out without injury.

On a AC breaker box this could easily end in death. Don't do it. I have seen people on accident take a hot DC lead and contact metal with it and not be injured. With AC that person most likely would have got knocked across the room. The one true thing about DC is you will have much larger cables. The longer the distance, the larger the cable (or the greater the number of circular mills as we like to call it). But we also run the voltage at -51.4 volts.

There are some very vague generalizations that people are making here that are incorrect. Please keep comments on safety accurate or don't comment. People feel like they have to know everything and just because a person does a quick google to pretend they know doesn't mean they do. I only joined to respond to this because there is misinformation being stated as fact here.
One correction on my prior post. Our rectifiers that convert AC to DC I guess run on AC. Thats it. Nothing else does. One other huge advantage to DC power is the amount of cooling required for DC is far less than that of AC. And Tesla himself was in fact trying to run DC to the home. The worst thing I have ever encountered in a DC power configuration: thermal runaway. But this is more due to the float voltage of the DC plant not being set correctly or not being checked over time to ensure it is still correct, which in turn overcharges the battery strings (we have batteries for everything) and explosive gas is released. But you could argue that is not really related to DC itself and I would agree. Thats more human error.

If you ever intend to run on a solar power configuration you will need to understand DC power and theory. Or it will be to your advantage to as the configuration for solar powered homes does use DC power. So if you want out of the AC rat race, go to solar when it becomes more cost effective.
King ZZ1 year ago
OK...

90% of my things run on DC current,
xbox, ps3, phones, TV(lcd etc), printers, everything I can see

Energy bulbs (these can run on dc or ac see youtube) /
LED household bulbs run on dc

i go into my kitchen and i think the toaster, kettle, microwave and fridge are all maybe 240vac

1) So why is the electric inside my home AC?
2) im not saying use 12VDC everywhere that would be ludicrous, but why is it not DC?
3) my xbox uses 12VDC and 5VDC same as my computer so obviously it can manage the change in voltage?
4) Could they not, with todays breakthroughs EITHER;
4a) Use High voltage DC to travel efficiently?
4b) or use the High voltage AC to travel, but when it reaches my home (or residential area) convert to 240VDC (or some ?VDC) instead of 240VAC

Then according to this really good youtube video ....

http://www.youtube.com/watch?v=xjHjFfp6PCg

There would be less loss,
Less heat coming from the laptop or the back of the TV....

and OMG maybe no more Red Ring Of Death on the xbox

(oops i forgot MS are scared you will not buy another, so the multi-billion dollar/pound company, that's been making processors and such things for a very long time and getting it right, seem to make an xbox that always goes wrong!!) Slightly off topic :-P
iceng King ZZ1 year ago
life must be tough for you
Dipankar (author) 2 years ago
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.
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
lemonie2 years ago
No, it's not.
This is what Edison used to say about the Westinghouse system.

L
Vyger2 years ago
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.
Ringing is AC.
Burf2 years ago
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.
Kiteman Burf2 years ago
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...
Dipankar (author) 2 years ago
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
Dipankar (author) 2 years ago
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
Re-design2 years ago
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).
framistan2 years ago
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.
Thermionic2 years ago
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":
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).
kelseymh2 years ago
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.
aelias362 years ago
Transformers only work with AC, so it's easier to use AC in the whole power grid.