22 Sep 05
I have been wondering whether it would be cheaper for governments to supply DC electricity to homes, perhaps alongside AC power.
I suppose the only home appliances that *need* AC supply are AC motors in pumps, and compressors in AC/Refrigerators.
Most lighting systems and displays should work with DC. Further, most digital systems invariably run on DC and have a rectifier (SMPS) to convert AC into DC.
The benefit would be the savings from eliminating these huge amount of rectifiers. Imagine all computers, LCD displays, cable modems, home stereo systems, mobile phone chargers, etc, directly being plugged into a DC power outlet, without a SMPS in-between.
The biggest savings might be from better UPS (Uninterrupted Power Supply) designs. At present, they have to convert from AC to DC to store the charge into their capacitors. At the output side, the power from the battery has to be reconverted to AC, which finally gets converted back into DC when it reaches your computer! Three stages of conversion AC->DC->AC->DC can be eliminated in one go...
22 Sep 05
1 edit
Interesting idea. Long-distance transmission lines are only efficient at really high voltage. I'm not sure how practical it is to step kilovolts DC down to mere volts DC at the substation where the transmission line enters a municipality, or what sort of equipment would do this. I seem to remember Edison himself pushing for DC powerlines early on.
22 Sep 05
Originally posted by Paul Diraci agree
Interesting idea. Long-distance transmission lines are only efficient at really high voltage. I'm not sure how practical it is to step kilovolts DC down to mere volts DC at the substation where the transmission line enters a municipality, or what sort of equipment would do this. I seem to remember Edison himself pushing for DC powerlines early on.
22 Sep 05
2 edits
Originally posted by ePharaohhttp://print.google.co.uk/print?id=lwTpCFh8S-EC&lpg=PA8&dq=why+is+mains+electricity+ac+not+dc&prev=http://print.google.co.uk/print%3Fq%3Dwhy%2Bis%2Bmains%2Belectricity%2Bac%2Bnot%2Bdc%26oi%3Dprint&pg=PA8&sig=JKrjImaLxhBPKrE2FlJJJ2BveN8
I have been wondering whether it would be cheaper for governments to supply DC electricity to homes, perhaps alongside AC power.
I suppose the only home appliances that *need* AC supply are AC motors in pumps, and compressors in AC/Refrigerators.
Most lighting systems and displays should work with DC. Further, most digital systems invariably run on DC ...[text shortened]... reaches your computer! Three stages of conversion AC->DC->AC->DC can be eliminated in one go...
Read the last paragraph of page 8 and the first two paragraphs of page 9.
Oh, the link's too blooming long. Generally what it says is that, DC power stations could only produce low voltage output. This meant, that to achieve the same power out put, the current had to be larger.
P = IV.
This required big fat cables which were totally impractical.
Also, long cable runs cause big voltage drops, which in turn means that DC cables can only be very short. This situation requires that lots of small power stations, built locally to where the power needed to be delivered. Meaning pollution close to houses.
AC power stations are capable of generating much higher voltages. These higher voltages make any voltage drop less dramatic, and also allow the usage of a much smaller current and thus, smaller cable. It also allows for long cable runs, and therefore, allows for a big ugly power stations pumping out pollution into the local countryside rather than on your doorstep. 😛
22 Sep 05
Originally posted by Paul DiracThe Edison vs. Westinghouse debate.
Interesting idea. Long-distance transmission lines are only efficient at really high voltage. I'm not sure how practical it is to step kilovolts DC down to mere volts DC at the substation where the transmission line enters a municipality, or what sort of equipment would do this. I seem to remember Edison himself pushing for DC powerlines early on.
Edison's idea was to generate DC power locally at the voltage it was to be used. Local generation would avoid excessive power line loss at the relatively low voltage.
Westinghouse favoured AC central power generation and distribution at high voltage with step-down transformers supplying the customer's end needs.
22 Sep 05
Originally posted by KneverKnightI think it was an Edison v Tesla debate. Tesla was a showman and a brilliant eccentric who was hooked on AC. A bit of a kook <sp?>.
The Edison vs. Westinghouse debate.
Edison's idea was to generate DC power locally at the voltage it was to be used. Local generation would avoid excessive power line loss at the relatively low voltage.
Westinghouse favoured AC central power generation and distribution at high voltage with step-down transformers supplying the customer's end needs.
I'm a techno-peasant when it comes to electricity, so can't discuss further.
22 Sep 05
Originally posted by buffalobillYes it was tesla-edison, tesla 1 edison 0 except it cost tesla his job,
I think it was an Edison v Tesla debate. Tesla was a showman and a brilliant eccentric who was hooked on AC. A bit of a kook <sp?>.
I'm a techno-peasant when it comes to electricity, so can't discuss further.
Edison does not like to be made to look wrong.
Enter the 21st century, great strides have been made in the
efficient conversion of AC to DC and back, and at extreme voltages,
one million volts so if we want to bad enough we can do DC to the
house if we want but that would require DC to DC converters in every
device not at the house voltage. The plus side to that is there should
be no debate over DC fields around powerlines and no buzzy crap
in our radios since DC does not emit RF, that by itself means more
efficiency over AC lines but I don't think the power companies
give a crap over how much RF buzz is foisted on an unsuspecting
public. BTW in the 1940's when car radios first started to be
popular, they found out they had to convert the 12 volts DC from the
battery to about 150 volts to run the radios which were made with
tubes long before modern transistor radios. The way they converted
the dc to ac was with a vibrating reed which alternately contacted
two lines to a transformer and you then had a form of AC, kind
of RF noisy but it worked. Now we do basically the same thing, send the
DC through two or more alternate paths and it does about the same
thing but with a lot less noise (there still is some) and no moving
parts just transistors, SCR packs and so forth, pretty efficient, some
of them running at 10 MHZ, the higher the frequency you make the
conversion the more efficient the whole process becomes. Anyway
thats the 50 cent tour of DC to DC conversion. Tesla would have
freaked out.
22 Sep 05
Originally posted by buffalobillWestinghouse was "inspired" by Tesla.
I think it was an Edison v Tesla debate. Tesla was a showman and a brilliant eccentric who was hooked on AC. A bit of a kook <sp?>.
I'm a techno-peasant when it comes to electricity, so can't discuss further.
"Edison was less than thrilled with the emergence of Westinghouse’s technology, which threatened his own dominance in a field he virtually created. He also had genuine concerns about the safety of AC. The two men engaged in a public relations battle to determine which system would become the dominant technology. In an attempt to discredit AC power Edison stooped to some low tricks. He paid schoolboys a quarter for each dog or cat they delivered to him and then he electrocuted the animals in deliberately gruesome public experiments. In another desperate attempt to sway public opinion against AC, Edison recommended that the state of New York use electrocution by means of AC power as its method of capital punishment. He even suggested calling the electric chair the “Westinghouse Chair” and recommended that the verb “Westinghoused” be used to describe electrocution."
from
http://www.ieee-virtual-museum.org/collection/event.php?id=3456872&lid=1
22 Sep 05
Originally posted by KneverKnightIn the electrical standards battle, Edison lost and probably was wrong. He obviously would not have enjoyed this. Here's another reference which looks pretty good:
Westinghouse was "inspired" by Tesla.
"Edison was less than thrilled with the emergence of Westinghouse’s technology, which threatened his own dominance in a field he virtually created. He also had genuine concerns about the safety of AC. The two men engaged in a public relations battle to determine which system would become the dominant technology. ...[text shortened]... trocution."
from
http://www.ieee-virtual-museum.org/collection/event.php?id=3456872&lid=1
http://en.wikipedia.org/wiki/War_of_Currents
22 Sep 05
Originally posted by KneverKnightTesla went off the deep end with his powering the ionosphere with
Westinghouse was "inspired" by Tesla.
"Edison was less than thrilled with the emergence of Westinghouse’s technology, which threatened his own dominance in a field he virtually created. He also had genuine concerns about the safety of AC. The two men engaged in a public relations battle to determine which system would become the dominant technology. ...[text shortened]... trocution."
from
http://www.ieee-virtual-museum.org/collection/event.php?id=3456872&lid=1
voltage meant to make the upper atmoshere one side of a gigantic
earth sized capacitor with high towers supposedly able to tap
energy off the ionosphere anywhere on earth, maybe it would have
even worked to a certain extent but I don't think he ever thought
past any possible consequences to this harebrained scheme.
He did design three phase ( I think he even tried 6 phase) electric
motors and generators and a guy named Stanley designed the
transformers when they wired up Niagra in 1879. No matter what
else people think of Tesla they have to recognize his brilliance in
the field of multiphase motors and generators.