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Old 12-10-2014, 05:38 PM
 
7,281 posts, read 8,837,177 times
Reputation: 11419

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Quote:
Originally Posted by jeffrow1 View Post
12 volt wiring is MUCH larger than AC. The cost of copper alone would make it a non-starter in my opinion. The cables for the windlass on my boat were larger than my thumb to only go 50 feet from the batteries.
That is because of the amperage, not the voltage. In many cases though, what you're talking about looks like it adds up because it comes up with high load equipment.

There is an easy solution for eliminating that heavy gauge cable you have going from the batteries to the windlass but that is best posted elsewhere. You've got a design issue.

In a house though, using 12 volt appliances, you can easily wire it without breaking the bank. The largest cabling will come into play for the distances between the charge controller and battery bank and then if you have an inverter, between that and the battery bank.

If you invert from the stored source to appliances, you can use the same wiring you would for any AC wiring design because that is what it is, AC.

A complete DC system in a residential design isn't cost prohibitive. Proper design can mitigate a lot of the costs.
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Old 12-10-2014, 06:12 PM
 
12,672 posts, read 9,911,944 times
Reputation: 9451
Quote:
Originally Posted by yellowsnow View Post
Everything we plug in the wall is AC. Why?

If power was DC, we could use solar more efficiently. There would be no conversion loss. I did a little looking online and I could find some version of almost everything that works on DC.

I figure there must be some over whelming reason we use AC. What is it?

Please excuse this question for being so basic.
You cannot have induction-based transformers with DC. These transformers are used to step up voltage at the generating station and then step it down at a distributing station for the neighborhood. Without this stepping up and down of voltage, you have higher currents in the long power lines which cause a large amount of energy loss.
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Old 12-10-2014, 06:51 PM
 
Location: Nebraska
4,231 posts, read 7,243,410 times
Reputation: 6685
Quote:
Originally Posted by yellowsnow View Post
Everything we plug in the wall is AC. Why?

If power was DC, we could use solar more efficiently. There would be no conversion loss. I did a little looking online and I could find some version of almost everything that works on DC.

I figure there must be some over whelming reason we use AC. What is it?

Please excuse this question for being so basic.
AC can be moved to distant areas more efficiently. DC power sources must be sited close to their end use. Solar is great during daylight hours but until someone invents a heckuva lot better storage method both Wind and Solar cannot compete.
GL2
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Old 12-10-2014, 07:26 PM
 
Location: DC
6,509 posts, read 6,430,643 times
Reputation: 3112
Quote:
Originally Posted by yellowsnow View Post
Everything we plug in the wall is AC. Why?

If power was DC, we could use solar more efficiently. There would be no conversion loss. I did a little looking online and I could find some version of almost everything that works on DC.

I figure there must be some over whelming reason we use AC. What is it?

Please excuse this question for being so basic.
You can use traasformer s to step AC voltage up and down. That allows power to moved across a large distance with only modest losses.
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Old 12-10-2014, 08:34 PM
 
208 posts, read 279,495 times
Reputation: 172
Notice how the secondary voltage is approximately ten times less than the primary voltage (0.9962 volts compared to 10 volts), while the secondary current is approximately ten times greater (0.9962 mA compared to 0.09975 mA). What we have here is a device that steps voltage down by a factor of ten and current up by a factor of ten:
http://www.allaboutcircuits.com/vol_2/chpt_9/2.html
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Old 12-10-2014, 08:40 PM
 
208 posts, read 279,495 times
Reputation: 172
Quote:
Originally Posted by yellowsnow View Post
Everything we plug in the wall is AC. Why?

If power was DC, we could use solar more efficiently. There would be no conversion loss. I did a little looking online and I could find some version of almost everything that works on DC.

I figure there must be some over whelming reason we use AC. What is it?

Please excuse this question for being so basic.
it's possible to transport AC hundreds of miles.
DC cannot be transported very far.
if we were to use DC, we'd have to have power plants every few miles.

there are many applications in which DC is better.
the San Francisco trolley system uses 600V DC.
(and i lived for a while in a hotel that used power from the trolley lines for it's elevator.)

however, transformers require DC.
in addition, induction motors, also called brushless motors, use DC and require less maintenance.

generally, for light bulbs, it doesn't make much difference which you use.
for motors, DC is more powerful, but DC motors wear more.
in a TV or computer, there is a power supply that does 2 things.
a) makes various AC voltages.
b) then converts the AC to DC.
that ability to change voltage is used many places, and would likely be sufficient justification to use AC in general.

when you add the efficiency in power transmission, the case completely favors AC.
Source:
http://en.wikipedia.org/wiki/War_of_Curr...
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Old 12-11-2014, 12:44 AM
 
Location: the Permian Basin
4,193 posts, read 3,062,936 times
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Quote:
Originally Posted by yellowsnow View Post
Everything we plug in the wall is AC. Why?
Because DC does not travel well over transmission & distribution lines.
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Old 12-11-2014, 08:52 AM
 
Location: NE Mississippi
13,469 posts, read 8,483,183 times
Reputation: 19583
Quote:
Originally Posted by yellowsnow View Post
Everything we plug in the wall is AC. Why?

If power was DC, we could use solar more efficiently. There would be no conversion loss. I did a little looking online and I could find some version of almost everything that works on DC.

I figure there must be some over whelming reason we use AC. What is it?

Please excuse this question for being so basic.
An inquisitive mind! I love it.

Interesting piece of history about that subject. The story involves Thomas Edison, Nicholas Tesla (the car named in his honor) and a man named George Westinghouse.

Westinghouse won, thanks to Edison's treatment of Tesla when Tesla worked for Edison. Well, that, and pure physics.

It's all great stuff, part of American History and the best way to put it all together is by watching the series "The Men Who Built America". I am such a fan of that series that I give the volume to someone every year for Christmas.
http://www.amazon.com/dp/B00A2XTJI4/...l_6816ztiyg0_b
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Old 12-11-2014, 10:10 AM
 
Location: Somewhere in northern Alabama
17,753 posts, read 53,902,796 times
Reputation: 30012
Some of the responses are "entertaining" to put it politely.

First, electronic appliances don't convert to DC for "convenience." Most electronics circuits operate only on DC and cannot operate on AC.

Second, a lot of posts confuse the attributes of AC vs DC with the attributes of voltage and amperage. High voltage transmission power can be (and sometimes is) transmitted as DC. While induction transformers can't be used to convert DC, motor-generators can, by using rotational energy as an intermediary.

It is largely irrelevant if power is AC or DC when deciding wire gauge. Voltage times amperage equals wattage. The higher the voltage, the lower the amperage needed to achieve the same wattage. If DC voltage was 120 volts, the same gauge wire would be used as in a comparable AC circuit using 120 volts.

Three phase motors are efficient for certain applications, but the DC traction motor is inherently FAR superior in others, and most homes only have split single phase power available anyway. A single phase AC motor can stall and "buzz" and provide little or no rotational thrust as it slowly cooks. A DC motor that is over-loaded will "lug down" and increase torque as the incoming voltage drops and amperage goes up. There is a reason that locomotives and streetcars normally use traction motors.

DC voltage will cause a muscle to strongly "lock up," making it impossible to break away from a gripped circuit unless an outside force is applied. AC is less likely to cause that reaction.

Primary reasons for using the higher voltages in home wiring are:
Increased efficiency
Reduced materials cost
Reduced fire risk
Increased safety

Last edited by harry chickpea; 12-11-2014 at 10:18 AM..
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Old 12-11-2014, 11:01 AM
 
12,672 posts, read 9,911,944 times
Reputation: 9451
Quote:
Originally Posted by harry chickpea View Post
Some of the responses are "entertaining" to put it politely.

First, electronic appliances don't convert to DC for "convenience." Most electronics circuits operate only on DC and cannot operate on AC.

Second, a lot of posts confuse the attributes of AC vs DC with the attributes of voltage and amperage. High voltage transmission power can be (and sometimes is) transmitted as DC. While induction transformers can't be used to convert DC, motor-generators can, by using rotational energy as an intermediary.

It is largely irrelevant if power is AC or DC when deciding wire gauge. Voltage times amperage equals wattage. The higher the voltage, the lower the amperage needed to achieve the same wattage. If DC voltage was 120 volts, the same gauge wire would be used as in a comparable AC circuit using 120 volts.

Three phase motors are efficient for certain applications, but the DC traction motor is inherently FAR superior in others, and most homes only have split single phase power available anyway. A single phase AC motor can stall and "buzz" and provide little or no rotational thrust as it slowly cooks. A DC motor that is over-loaded will "lug down" and increase torque as the incoming voltage drops and amperage goes up. There is a reason that locomotives and streetcars normally use traction motors.

DC voltage will cause a muscle to strongly "lock up," making it impossible to break away from a gripped circuit unless an outside force is applied. AC is less likely to cause that reaction.

Primary reasons for using the higher voltages in home wiring are:
Increased efficiency
Reduced materials cost
Reduced fire risk
Increased safety
Transformer with moving parts = lots of wear and tear...
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