AC vs. DC ?

[GigaCluster]

I hear that DC power is better for most devices, and they'd be able to take advantage of DC much better than of AC. (perhaps that's why most expensive devices come with DC converters.)

Is that true?

If so, why not have a special transformer that converts from AC to DC going to each house? I can see how DC would be horrible to transmit over long distances and with such high voltage, but if DC is so much better than AC, I think it would be nice for DEFAULT current in the house to be DC.

Any thoughts?

 

[Monel Funkawitz]

<< I hear that DC power is better for most devices, and they'd be able to take advantage of DC much better than of AC. (perhaps that's why most expensive devices come with DC converters.)
>>



No. Devices that use IC's ALWAYS use DC. You can't create a binary signal with AC. Some items have a DC "wall wart" and others use a AC "wall wart". Only difference is the recifier bridge/diodes/filters/etc are in the power supply and not the unit itself, usually to save room.

AC is more efficient to send over long distances, and to run motors with.



<< If so, why not have a special transformer that converts from AC to DC going to each house? I can see how DC would be horrible to transmit over long distances and with such high voltage, but if DC is so much better than AC, I think it would be nice for DEFAULT current in the house to be DC.
>>



Why? Who is going to pay for this added expense? You know how inefficient a 250 amp AC/DC converter is? Plus added heat, parts, another thing to fail, etc. and for what? What gain? There is none. What sense does it make for me to take AC, convert it to DC, then convert it to AC to run my motors and lights? How are you going to make a flourescent light work on DC? How are you going to make a alarm clock stay accurate on DC, and keep the cost down? I am going to have to buy all new appliances in my house to run on DC then.

A "Whole House" AC to DC converter is a really bad investment idea, to say the least.

 

[Demon-Xanth]

AC does voltage conversion so much easier than DC that not using it in homes would be stupid. Also many applications are better with AC motors than DC motors (torque curves). Any AC/DC conversion should be done at the device level as it is now.

And not all ICs require DC. Just the vast majority of them.

 

[GigaCluster]

Okay. Thanks for enlightening me.

 

[ViperMagic]

Ain't got no gun... ain't got no knife...... but don't you start no fight, cuz im TNT, i'm dynamite

 

[Androck99]

Well, if you want to transmit DC over long distances, you have to have an insane about of Current to do this and you encounter a large amount of I^2*R(current squared times resistance) loss. With AC on the other hand, you can transmit over long distances with high Voltage and relatively low Current. High Voltage is much safer than high Current too...

 

[jhu]

she's got big balls, but he's got the biggest one of them all

 

[db]

Aside from the above issues, is there a safety advantage of one over the other (talking house current)?

 

[jthsmak]

this sums it up
(AC power) DONE DIRT CHEAP

 

[rival]

DC does some mean damage to you, some people get only a minor shock from 120v ac, while 90vdc (which i *think* is the voltage running in your phone lines when it rings) gets you pretty bad...DC at higher voltages is alot more dangerous, AC is safer...no link on this info however

 

[Theslowone]

AC is more efficient and easy to produce, The main place i see large amounts of dc being used is in large drives and brakes, where the chattering is less in dc then ac. But the rest of the system that they are on is still ac. They just convert just as it goes out.

And rival is right ac will hurt you but dc is a lot more apt to kill you.

 

[Midnight Rambler]

Ol' Thomas Edison sure wanted DC too ...

 

[Bozz]

To correct a few posts -

DC is better for long distance transmission specifically. Loss through inductance is minor yet measurable with 50 or 60Hz AC current over mass distance and DC does not produce alternating magnetic fields that many blame for cancer and other genetic and health problems. DC has a constant magnetic field that does not alternate, I dont consider myself an expert on human tissue reaction with electromagnetic fields but I would think that walking into a field and staying there for a period of time would be less harmful than walking into an alternating field that rises and collapses 100 or 120 times per second.

Like posted, AC is easier to create. Your car's alternator generates AC then rectifies it to DC then uses the battery as a smoothing capacitor to supply the electrical circuits

The big difference is what can be done with AC. The only active way to convert voltages is to create a changing current, hence AC. DC voltages can be reduced using passive components (resistors, diodes, transistors etc) but you cannot increase a DC voltage. I occasionally think to myself it would be better to have DC going through the house wiring for health reasons and to have a small shielded switchmode power supply wherever different voltage is required.

It is not feasable however to have a mass distribution of DC around a continent.

Cheers

 

[Androck99]

Hey Bozz, what the hell do you mean DC is better for long distance transmission? And if it's so much better than AC why do you say that it's "not feasable however to have a mass distribution of DC around a continent"?

 

[Bozz]

<< Hey Bozz, what the hell do you mean DC is better for long distance transmission? And if it's so much better than AC why do you say that it's "not feasable however to have a mass distribution of DC around a continent"? >>



Take it easy, I mean DC is better for long distance transmission SPECIFICALLY, re-read my post. DC is not affected by inductance. DC is good for long distance transmission but it is simply not feasable because at the end of the transmission line it would have to be converted to AC again.

The reason it is not feasable to have mass distribution of DC around a continent is because of voltage drop across wiring, if you re-read my post you will see I wrote that AC voltage can be increased and decreased, DC can only be decreased. Welcome to the world of regulation, to regulate the voltage you have coming into your house the power substations do that with AC, it cannot be done with DC. That is why it is not feasable. Hence why we have AC instead of DC. I could go on but I suggest you read a book instead that explains what inductance is (not a 2 page description, i mean a BOOK on inductance) and you will learn the many different reasons AC is a preferable choice for a continental electricity distribution grid.

DC is still better for long distance tranmission though

Cheers

 

[UNIX72]

I worked for a hugh telecomm company. All of our equipment runs on DC but why? Engineers told me its better to use DC in our enivornment but why? Thanks