U.S. CitiesCity-Data Forum Index
Covid-19 Information Page
Go Back   City-Data Forum > General Forums > Science and Technology
 [Register]
Please register to participate in our discussions with 2 million other members - it's free and quick! Some forums can only be seen by registered members. After you create your account, you'll be able to customize options and access all our 15,000 new posts/day with fewer ads.
View detailed profile (Advanced) or search
site with Google Custom Search

Search Forums  (Advanced)
Reply Start New Thread
 
Old 05-24-2020, 12:19 PM
 
2,591 posts, read 4,970,772 times
Reputation: 986

Advertisements

DC is mostly batteries, including car batteries. AC mostly means plugging something into a wall outlet.

But don't some appliances use DC although they are using an AC power cord? Like landphones or even internet routers?

I was a power cord for an internet router. It said "AC Adaptor" - not just AC power cord. Why would it be called that (it might be a mistake)?

I don't understand alternating current in general - if you are powering something like a vacuum cleaner, why would you want to the power to alternate directions instead of steadily going in one direction? I read the wikipedia articles about both forms of energy.
Reply With Quote Quick reply to this message

 
Old 05-24-2020, 12:46 PM
 
Location: Old Hippie Heaven
21,028 posts, read 9,657,687 times
Reputation: 12912
Quote:
Originally Posted by robertpasa View Post
DC is mostly batteries, including car batteries. AC mostly means plugging something into a wall outlet.

But don't some appliances use DC although they are using an AC power cord? Like landphones or even internet routers?

I was a power cord for an internet router. It said "AC Adaptor" - not just AC power cord. Why would it be called that (it might be a mistake)?

I don't understand alternating current in general - if you are powering something like a vacuum cleaner, why would you want to the power to alternate directions instead of steadily going in one direction? I read the wikipedia articles about both forms of energy.
Yes. Anything that has a "wall wart" - like your laptop, your camera, your router - actually runs on DC. The adapter just turns AC back into DC. (Do not ask me why that makes sense, I dunno. Maybe just because most homes don't have 12-volt outlets.)

I'm no expert, but I have always understood that AC was adopted as the standard for the grid because AC transmission is more efficient than DC over long distances. But if you want to wring every last bit of power out of your nearby power source, DC is better. Which is why truckers and RVers use DC appliances in their rigs - they can run their appliances (12v fridge, 12v cookers, 12v TVs) using smaller capacity batteries. Quite a few people who build out their own vans carry only DC appliances.
Reply With Quote Quick reply to this message
 
Old 05-24-2020, 12:47 PM
 
1,963 posts, read 503,478 times
Reputation: 3165
In a nutshell, AC power is both more "compact" and has far lower losses in transmission over the wires. All things being equal, AC delivers more usable energy than DC, especially when you get to the potent 3-phase type (used at higher voltages for things like compressors, large equipment, etc.)

While lots of things use DC as the final form, in their circuitry and motors, the voltage can vary from 1.5 to 90 volts, with most being maybe 5-24 volts. You could have a DC power bus in your house, but it would still have to be adapted to each device (or vice versa); the easiest way to convert voltages is by stepping down AC with a transformer and then converting it to DC. DC-DC conversion can be done, and a higher DC voltage can be limited and regulated to a lower one, but overall a relatively high-voltage AC source is the easiest and simplest way to power everything from your fridge to your phone charger.

DC also travels very poorly over transmission lines. I forget specifics, but a DC generating plant can only send power a few miles before losses become unacceptable; AC power can be transmitted thousands of miles with manageable losses.

A power cord usually carries wall-socket juice (125V AC) directly to the device, where it might be used directly to drive a motor or stepped down through a small transformer and converted to DC.

A power adaptor takes wall juice and sends only the converted (usually DC and much lower voltage) power to the device. Adaptors are used for two reasons: it means a suitable adaptor can be used to power the device anywhere in the world, regardless of local voltage or AC frequency, and by using an adaptor already certified as safe according to UL or TUV or other national safety agencies, you don't have to have the device itself certified as safe.

Just to confuse things, there are (or used to be) 32-volt DC appliances first intended for use in rural areas with a Wincharger wind-driven generator, and these were adapted to at least one generation of RVs. Not sure if anything like these still exists. Converting a battery rack to regular AC power using an inverter has become more common, I think,
Reply With Quote Quick reply to this message
 
Old 05-24-2020, 12:51 PM
 
2,591 posts, read 4,970,772 times
Reputation: 986
Thank you.

By the way, routers and similar devices have a metal cylindrical power plug. What is that plug called exactly?
It might be just 12V - but I've seen "12V 1A" or "12V 3A".
Reply With Quote Quick reply to this message
 
Old 05-24-2020, 01:25 PM
 
1,963 posts, read 503,478 times
Reputation: 3165
Quote:
Originally Posted by robertpasa View Post
Thank you.

By the way, routers and similar devices have a metal cylindrical power plug. What is that plug called exactly?
It might be just 12V - but I've seen "12V 1A" or "12V 3A".
No special name, usually just "power connector." There is an entire taxonomy of those round, coaxial connectors based on outside diameter, inside diameter and insertion length, in millimeters. In theory they are supposed to be sorted according to the supplied voltage (and current rating), but in practice it's almost completely random and driven by every engineering and marketing reason except anything sensible.

The marking near the port is the nominal supply voltage and required current. Although the device probably has internal regulation and limiting, it's best to stay as near that voltage as possible when using a replacement power adaptor. Lower voltage might not work; higher voltages could damage the unit or at least generate a lot of heat from the power limiting circuitry.
Reply With Quote Quick reply to this message
 
Old 05-25-2020, 11:41 AM
 
Location: Not far from Fairbanks, AK
17,078 posts, read 30,221,884 times
Reputation: 12991
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
Reply With Quote Quick reply to this message
 
Old 05-25-2020, 12:06 PM
 
1,963 posts, read 503,478 times
Reputation: 3165
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.
Well... AC is very rarely used in 'circuitry' unless it's for the somewhat circular purpose of controlling AC power. And within a compact vehicle, DC losses are so low there's no good reason to use an AC power bus. And, just to be really persnickety, AC power tends to run at a low and very precise/stable frequency; I can assemble a simple 60Hz+harmonics filter behind my back while half asleep.

Even in most modern cars, an alternator generating AC power is used only for its exceptional weight/power advantage over a DC generator... and the AC does not leave the unit, but is rectified to DC right at its terminals.

But true. DC essentially generates no noise except when (like all power) it's switched on or off.
Reply With Quote Quick reply to this message
 
Old 05-25-2020, 08:39 PM
Status: "Trump is orange buffoon" (set 13 days ago)
 
Location: Berkeley, Denver, CO USA
14,925 posts, read 22,237,947 times
Reputation: 25243
Quote:
Originally Posted by Therblig View Post
While lots of things use DC as the final form, in their circuitry and motors, the voltage can vary from 1.5 to 90 volts,
Not true.
Most tram systems use DC voltages at 600-900.
Reply With Quote Quick reply to this message
 
Old 05-25-2020, 09:37 PM
 
1,963 posts, read 503,478 times
Reputation: 3165
Quote:
Originally Posted by davebarnes View Post
Not true.
Most tram systems use DC voltages at 600-900.
You have a tram system in your house?

(I was referring to the range of DC voltages in household stuff. Otherwise I'd bring up 100-300kV DC transmission lines. )
Reply With Quote Quick reply to this message
 
Old 05-25-2020, 10:18 PM
 
Location: Not far from Fairbanks, AK
17,078 posts, read 30,221,884 times
Reputation: 12991
Quote:
Originally Posted by Therblig View Post
Well... AC is very rarely used in 'circuitry' unless it's for the somewhat circular purpose of controlling AC power. And within a compact vehicle, DC losses are so low there's no good reason to use an AC power bus. And, just to be really persnickety, AC power tends to run at a low and very precise/stable frequency; I can assemble a simple 60Hz+harmonics filter behind my back while half asleep.

Even in most modern cars, an alternator generating AC power is used only for its exceptional weight/power advantage over a DC generator... and the AC does not leave the unit, but is rectified to DC right at its terminals.

But true. DC essentially generates no noise except when (like all power) it's switched on or off.
In aircraft communication systems, DC power is used because it does not interfere with nearby electrical systems. AC power is too noisy.

https://www.electricaltechnology.org...ac-and-dc.html
Quote:
In DC System, there is no interference with other communication lines and systems.
That said, the primary aircraft generators produce AC power. Ac power is also used for the landing lights, strobe lights, and so on. But numerous aircraft systems depend on DC power. If you look at most aircraft wire harnesses, you will notice that the wires ave very thin (16-22 gauge). If you were to use AC power only, these wires would be quite heavy because of the layer of insulation they would need.
https://www.falconups.com/Optimizing_Aircraft_Power.pdf
-----------

I would like to apologize to the OP since his questions was related to DC power for home use. However, if he wants to see what the pros and cons of AC power versus DC power at home are, then just read what is said it the first link I posted above. The second link is about aircraft power.

Last edited by RayinAK; 05-25-2020 at 10:49 PM..
Reply With Quote Quick reply to this message
Please register to post and access all features of our very popular forum. It is free and quick. Over $68,000 in prizes has already been given out to active posters on our forum. Additional giveaways are planned.

Detailed information about all U.S. cities, counties, and zip codes on our site: City-data.com.


Reply

Quick Reply
Message:

Over $104,000 in prizes was already given out to active posters on our forum and additional giveaways are planned!

Go Back   City-Data Forum > General Forums > Science and Technology
Similar Threads
Follow City-Data.com founder on our Forum or

All times are GMT -6.

© 2005-2020, Advameg, Inc. · Please obey Forum Rules · Terms of Use and Privacy Policy · Bug Bounty

City-Data.com - Contact Us - Archive 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37 - Top