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Old 05-26-2020, 11:52 AM
 
Location: Mars City
5,894 posts, read 2,766,526 times
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Some devices need AC (electrical current that oscillates back and forth in direction). Many others can go with the simpler, less energetic DC (current flows in one direction only).

Yes, many devices run off of converters, which take the 120 volts AC from the wall, and convert them down to not only DC (which is less dangerous), but also a lower and less dangerous voltage.

120 VAC offers a lot, so it makes sense to provide that maximum capability in the homes, offices, and buildings. For the many things that don't need that, we have an easy way to modify it down to something simpler and safer. It'd be completely ridiculous and inefficient to go the other way.
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Old 05-26-2020, 03:36 PM
 
1,402 posts, read 871,825 times
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It's all about power distribution and the electrical grid which is AC for a reason.
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Old 05-29-2020, 11:58 PM
 
Location: Myrtle Creek, Oregon
14,333 posts, read 13,895,434 times
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An alkaline battery is 1.2 vdc
Cell phone chargers are 5 vdc.
Vehicle electronics and appliances are 12 vdc
Battery power tools typically run at 20 vdc
Airplane instruments and many diesel starting systems are 24 vdc
Universal motors, the kind with brushes, will run on 120 vac or 90 vdc.
Chances are your house transformer is fed with 1200 vac, or a multiple of that voltage
Your power substation is probably fed with 115,000 vac
The high voltage long distance transmission lines run up to 1,200,000 vac
If the US ever builds a national electrical grid, it will need to run high voltage DC to avoid inductive losses. Stepping DC up and down is tricky and expensive, because you can't use transformers.
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Old 05-31-2020, 01:16 PM
 
Location: Not far from Fairbanks, AK
17,081 posts, read 30,221,884 times
Reputation: 12996
Lest not forget that a great number of devices at home use DC power. While the input power is AC, this power is converted to DC and is used by the electronic circuits inside of the device. For example, computers have a power supply that runs on AC power, this AC is transformed to DC and distributed to the rest of the computer. Then Once can plug-in the cellphone to the AC outlet to charge the battery, but the battery itself is a DC-power storage component (the cellphone uses this DC power to operate). Even TV's internal circuitries run on DC power.

https://computer.howstuffworks.com/power-supply.htm
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Old 06-06-2020, 05:02 PM
 
35,656 posts, read 18,394,808 times
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FWIW, there was a move towards DC in large data centers. Imagine a few thousand racks, all loaded up with servers, switches, storage arrays and whatnot. Each of these device - and there are tens of thousands in a large data center - has one or more converters from 240V or 120V AC to (typically) 48V DC. This is tremendously inefficient, there's a huge heat loss, and - as anyone will tell you - the damn power supplies keep breaking.

What if - we instead put some huge converters to 48V DC in central spots and provided 48V directly to the eelctronics? It's readily agreed that it works, but adaptation has been very half-hearted - there's a definite "the devil I know" attitude. Which is too bad, it's elegant engineering.
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Old 06-06-2020, 05:17 PM
 
1,972 posts, read 503,478 times
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Quote:
Originally Posted by Dane_in_LA View Post
FWIW, there was a move towards DC in large data centers. Imagine a few thousand racks, all loaded up with servers, switches, storage arrays and whatnot. Each of these device - and there are tens of thousands in a large data center - has one or more converters from 240V or 120V AC to (typically) 48V DC. This is tremendously inefficient, there's a huge heat loss, and - as anyone will tell you - the damn power supplies keep breaking.

What if - we instead put some huge converters to 48V DC in central spots and provided 48V directly to the eelctronics? It's readily agreed that it works, but adaptation has been very half-hearted - there's a definite "the devil I know" attitude. Which is too bad, it's elegant engineering.
Going from the very specialized situation of a server farm to the idea that we have to have a distribution network just for the electronics is... oddly entertaining. But, uh, on a par with running USB charging power city wide.
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Old 06-11-2020, 12:35 PM
 
Location: Portland, OR
1,223 posts, read 1,937,016 times
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Quote:
Originally Posted by RayinAK View Post
One thing about DC is that it produces less noise. That's a reason while DC is useful in aircraft circuitry.

https://www.electricaltechnology.org...ac-and-dc.html

It is? News to me.... As a pilot. Yes, small general aviation aircraft may use 12V, but all commercial aircraft use 115v 400Hz ac. 400Hz because the higher frequency means that power converters can use smaller, lighter transformers.
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Old 06-11-2020, 12:39 PM
 
Location: Portland, OR
1,223 posts, read 1,937,016 times
Reputation: 1637
Quote:
Originally Posted by Dane_in_LA View Post
FWIW, there was a move towards DC in large data centers. Imagine a few thousand racks, all loaded up with servers, switches, storage arrays and whatnot. Each of these device - and there are tens of thousands in a large data center - has one or more converters from 240V or 120V AC to (typically) 48V DC. This is tremendously inefficient, there's a huge heat loss, and - as anyone will tell you - the damn power supplies keep breaking.

What if - we instead put some huge converters to 48V DC in central spots and provided 48V directly to the eelctronics? It's readily agreed that it works, but adaptation has been very half-hearted - there's a definite "the devil I know" attitude. Which is too bad, it's elegant engineering.

Not really accurate. 48V was used as it would allow re-use of telecom related power and UPS backup technology. Each server still has a power supply to convert from 48V to 3.3V, 12V and other core voltages. Yes 48V was also chosen to reduce power conversion efficiencies.
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Old 06-11-2020, 12:41 PM
 
Location: Portland, OR
1,223 posts, read 1,937,016 times
Reputation: 1637
Quote:
Originally Posted by Larry Caldwell View Post
An alkaline battery is 1.2 vdc
Cell phone chargers are 5 vdc.
Vehicle electronics and appliances are 12 vdc
Battery power tools typically run at 20 vdc
Airplane instruments and many diesel starting systems are 24 vdc
Universal motors, the kind with brushes, will run on 120 vac or 90 vdc.
Chances are your house transformer is fed with 1200 vac, or a multiple of that voltage
Your power substation is probably fed with 115,000 vac
The high voltage long distance transmission lines run up to 1,200,000 vac
If the US ever builds a national electrical grid, it will need to run high voltage DC to avoid inductive losses. Stepping DC up and down is tricky and expensive, because you can't use transformers.

Eh? I think we already have a national electrical grid, and it runs on AC...
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Old 06-11-2020, 12:44 PM
 
Location: Portland, OR
1,223 posts, read 1,937,016 times
Reputation: 1637
Quote:
Originally Posted by Thoreau424 View Post
Some devices need AC (electrical current that oscillates back and forth in direction). Many others can go with the simpler, less energetic DC (current flows in one direction only).

Yes, many devices run off of converters, which take the 120 volts AC from the wall, and convert them down to not only DC (which is less dangerous), but also a lower and less dangerous voltage.

120 VAC offers a lot, so it makes sense to provide that maximum capability in the homes, offices, and buildings. For the many things that don't need that, we have an easy way to modify it down to something simpler and safer. It'd be completely ridiculous and inefficient to go the other way.

220VAC, as used in all of Europe, makes a lot more sense than 120V. Power distribution is more efficient and you can get a lot more power out of a 220V wall socket. I wish the US would get with the 21st century and use a more efficient voltage in the home, apart from the range and clothes dryer....
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