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...
Originally posted by ePharaohI'm guessing line loss across looooong wire lengths would make this idea really impractical. AC allows the use of transformers for load isolation, too.
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...
Originally posted by ePharaohDC is really dangerous, or so I have heard. Supposedly if you electrocute yourself with AC your heart will beat at the frequency of the AC, but if you electrocute yourself with DC your heart will just stop.
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...
Wikipedia has an interesting article on this topic:
http://en.wikipedia.org/wiki/War_of_Currents
EDIT - Actually, that article claims AC is more dangerous. Guess I don't know what I am talking about!
It would be cool if hearts could synchronise with the AC supply. Then all hearts could be synchronised together. And when somebody had high BP, the extra power could be used to power the heart of someone with a low BP.
š
Hmm.. looking at the wikipedia article...
It seems like AC is good for macro distribution. But perhaps at the micro-level, say a single block or locality, we could have a single transformer for AC->DC rather than tens of them in every home.
current is the key, fatal current is 100-200 mA, below that there's no fibrillation, above that the heart clamps and there's no fibrillation, in between you get fibrillation.
fatal voltage can be as low as 42 volts DC ... skin resistance plays a role, wet skin being less resistant ...
http://www.google.com/search?hl=en&ie=ISO-8859-1&q=%22the+fatal+current%22
Originally posted by XanthosNZcould not find the original paper, "The Fatal Current" by the Fluid Controls Company, this contains a portion:
I took 150VAC at 0.3A with no ill effects once I could move my legs again.
I didn't realise a motion sensor buzzer would pack that much punch.
http://www.colorado.edu/physics/phys3330/phys3330_fa02/Syllabus.pdf
300 mA at the buzzer, but your skin resistance unless wet could be as much as 500K.
"From a practical viewpoint, after a person is knockedout by an electrical shock it is impossible to tell how much current passed through the vital organs of their body. Artificial respiration must be applied immediately if breathing has stopped. ... The skin resistance may vary from 1000 Ω for wet skin to over 500,000 Ω for dry skin."
so in your case the current could have been 0.3 to 150 mA. unless a wire poked through your skin.
Originally posted by ePharaohWow, never heard of a heart beating at 50 or 60 beats per second.
It would be cool if hearts could synchronise with the AC supply. Then all hearts could be synchronised together. And when somebody had high BP, the extra power could be used to power the heart of someone with a low BP.
š
Hmm.. looking at the wikipedia article...
It seems like AC is good for macro distribution. But perhaps at the micro-level, say a si ...[text shortened]... locality, we could have a single transformer for AC->DC rather than tens of them in every home.
That would be some sync!
Your second point about the transformer, transformers only change
the voltage or current of AC, they never ever put out DC.
You could have power supplies after the transformer but some
gadgets REQUIRE AC to work. Like Flourescent lighting for instance,
they have rather stringent voltage requirements like a high peak to
strke an arc then a lower voltage to run, done by a beast called
the Ballast. Likewise with the light bulb sized flourescents, the spiral
ones. They have electronics inside that depends on the voltage
being ac. Then there are air conditioners, refrigerators, oil burners,
TV's. They all require ac inputs because they have really disparate
voltage requirements for differant circuits. Oil burners for instance,
use the ac and up-convert it to about 10,000 volts so it can
strike an arc continuously and safely. Thats what keeps the oil
burning. It would be possible to do all of the above job starting with
DC but it would require retooling, reengineering EVERYTHING.
There are only two gadgets that don't give a crap about ac or dc:
incadescent lights and electric heaters. Even there, running them on
DC may lower the life. There are effects that happen in vacuum
where using dc to power stuff causes differant build-ups of ions
on the positive electrode vs the negative electrode. That can
lead to selective corrosive effects lowering the lifespan of certain
gadgets. Running them on AC ensures there will be no selective
build up on each electrode, both electrodes will have just about the
same amount of crud on each one.
Originally posted by zeeblebotPretty good analysis for a software engineer! Shows you got more
could not find the original paper, "The Fatal Current" by the Fluid Controls Company, this contains a portion:
http://www.colorado.edu/physics/phys3330/phys3330_fa02/Syllabus.pdf
300 mA at the buzzer, but your skin resistance unless wet could be as much as 500K.
"From a practical viewpoint, after a person is knockedout by an electrical shock it ...[text shortened]... in your case the current could have been 0.3 to 150 mA. unless a wire poked through your skin.
classes than just running bits around, eh! I was going to jump on
that one if you hadn'tš You can't just assume 150 V ac or dc will
cause X amount of current to flow unless you know the resistance,
which as you pointed out could be less than 1000 ohm or hundreds
of times higher. It would only draw 300 MA at 500 ohms, pretty
low for skin, even wet skin. Possible though.
Originally posted by sonhouseMSEE working as a software engineer š ...
Pretty good analysis for a software engineer! Shows you got more
classes than just running bits around, eh! I was going to jump on
that one if you hadn'tš You can't just assume 150 V ac or dc will
cause X amount of current to flow unless you know the resistance,
which as you pointed out could be less than 1000 ohm or hundreds
of times higher. It would only draw 300 MA at 500 ohms, pretty
low for skin, even wet skin. Possible though.
Originally posted by PullhardThat comes from the specs on a power supply or electric gadget,
How do you know it was 0.3 A ?
IT takes 150 VAC at 0.3 amps to run.
A lot of people assume then thats what they absorb in energy,
150 volts, 1/3 amp about, = 50 watts. Its the skin resistance
that says what the current rating is, that and the impedence of the
power supply. If the supply was putting out its max of 0.3 amp
and could pump no more at 150 volts then the impedence would
be 50 ohms. So if for some reason the skin resistance went to
25 ohms, the voltage would drop in half to about 75 volts but
still equal 0.3 amps. However, now you have an impedence
mismatch and the max power cannot be transmitted. Now the
supply is only putting out 25 watts instead of 50 watts.
But with a skin resistance of 1500 ohms, the supply could
put out 150 volts but the 1500 ohms would ensure only 0.1 amp
would be flowing so now your body would be absorbing only
15 watts. At 3000 ohms, your body would only absorb 7 watts.
Etc.