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Comment: Re:Even if you go DC, stay at 120V (Score 1) 474

Everything from your wall switches to your wires will cause you never ending problems.

Mechanical wall switches are still rated for DC. Houses USED to be wired for DC a lot. You only have to replace the stuff that was designed after AC was pervasive and wasn't engineered to handle DC.

(I forgot to mention that you'll also have to replace the light dimmers, too, along with most other electronic, rather than mechanical, switches. They usually use a current-zero-crossing turnoff device, and DC won't cross zero unless you force it to do so.)

Even if you replace your wall switches and outlets, your wires will degrade over time and develop holes and other blemishes that will cause a fire.

No they won't - unless they're wet (in which case you have bigger problems than galvanic corrosion). Electromigration at the current densities involved in house wiring is not an issue, nor is insulation breakdown. The wires and fittings will be just fine.

Comment: Re:Even if you go DC, stay at 120V (Score 1) 474

(DANG this stupid touchpad... )

An "inverter", by definition, actually has alternating voltage as a substantial output, or at least somewhere in the circuitry. A switching regulator has a cycling voltage, but it isn't an AC output, or even an AC intermediate.

But they're very similar.

(Also: I was going to mention, above, that the current supplied through the pull-down (or clamp-at-ground) switch is where the extra output current comes from, compensating for the lowered voltage with higher current for similar amounts of power. If the switches, inductors, capacitors, and wiring were all ideal, the driver and sensor circuitry didn't eat any power, and no energy was radiated away as radio noise, efficiency would be 100%.)

Comment: Re:Even if you go DC, stay at 120V (Score 1) 474

A down-stepping DC-DC converter is not an inverter?

Nope. But the pieces of the implementations are similar enough in function that it's close.

A typical DC/DC down converter involves two switches, an inductor, and both input and output filter capacitors, plus control circuitry to sense the output voltage and time the switches. (There may also be a VERY small resistor in series with the inductor to sample the output current if current regulation is necessary, but it's omitted for high efficiency if that's not an issue.) One end of the inductor is hooked to the output cap, the other through the switches to the input cap and to ground.

The pull-up switch is always active (typically a transistor). The control circuitry turns it on and the current in the inductor ramps up, charging the output capacitor at an increasing rate. After a while the pull-up switch is turned off and the pull down switch is turned on. The current through the inductor ramps down, but before it goes through a stop and reverses the pull-up switch is turned back on and the pull-down turned off. The pull-down switch may be a diode, which switches on as needed automatically, but for high efficiency it's usually another transistor, because it has a lower voltage drop and thus is more efficient.

The control circuitry varies the percent of pull-up versus pull-down time to keep the average output voltage at the desired level. The frequency may be controlled or may be allowed to vary somewhat.

So the waveform in the inductor is a sawtooth, and the current never reverses. An "inverter" by definition,

Comment: Re:Even if you go DC, stay at 120V (Score 4, Interesting) 474

(Continuing after brushing the touchpad posted it for me. B-b) ... equipment at that voltage. (Small systems are often 12V due to the availability of 12V appliances.)

But back to inverters:

Current inverter and switching regulator (they're pretty much the same stuff) technology is SO efficient that large PC boards in computing and networking equipment may run the power through as many as THREE DC-DC converters, because you lose less power to heat as losses in the inverters than you would to resistance running it a few inches through a printed circuit board power plane.

So the '"20-40% loss" number seems to me to be utterly bogus.

(Consider this: A Tesla automobile IS AC motors driven by inverters from batteries. A horsepower is almost exactly 750 watts. If they had 20-40% losses in the inverters, how do you keep the car from being on fire after a jackrabbit start? Let alone recover enough power on braking to reuse on acceleration to make a substantial difference?) If ANYBODY knows how to handle inverters it's Tesla. B-) )

Comment: Even if you go DC, stay at 120V (Score 4, Interesting) 474

This is strange. "20 to 40% power loss" seems to be an awfully poor inverter; existing inverters are 4-8 % loss.

Rather than rewire every house in America, wouldn't it make more sense to just design better inverters?

Or just run at 120V DC, as renewable energy systems did (and occasionally still do) before so many appliances were AC-only that it made sense to use an inverter.

Dropping voltage means you have to replace the copper wiring with MUCH HEAVIER wiring - by a square law - to carry a given amount of power with the same loss - and thus wiring heating inside the walls, where it can set the house of fire.

Switching to 120V just means using DC-capable appliances and replacing the breakers (DC is harder to interrupt) and must-be-GFCI outlets (normal GFCI devices use a transformer to sense unbalanced load).

The 48V standard was about having a voltage that was low enough that touching it was typically survivable, so working on or near it is (relatively) safe. The boundary between the hard part and the easy, "low-voltage", part of the electrical code is 50V (BECAUSE of phone companies B-) ). Medium power (>1KW) home Renewable Energy systems tend to be at 48V so much of the wiring falls under the easier part of the code, and because of the availability of

Comment: Re:faster than light never violates Relativity (Score 5, Interesting) 201

by catmistake (#49789667) Attached to: Ways To Travel Faster Than Light Without Violating Relativity

You're at a very straight, very long beach. Imagine parallel waves striking the shore at a vanishingly slight angle. The point that the wave meets the shore moves along as the intersection of wave and beach occurs. As the waves get closer and closer to parallel with the beach, but not quite parallel, eventually that intersection point will be moving much faster than c.

But the interesection point between waves and shore doesn't have mass, isn't really a "thing" that's moving.

Comment: Re:faster than light never violates Relativity (Score 4, Informative) 201

by catmistake (#49789507) Attached to: Ways To Travel Faster Than Light Without Violating Relativity

Relativity requires that nothing can move through space faster than light.

Relativity requres that nothing can move through space as fast as light (c). Nothing with mass moving slower than c can reach c by moving faster, due to increase in mass and infinite energy required to reach c, and nothing moving faster than light can slow down to c, for the same reasons. The quote from teh article is at best misleading and at worst, false.

Comment: Not if they think they can get more work out of us (Score 1) 131

by Ungrounded Lightning (#49788985) Attached to: Scientists Reverse Aging In Human Cell Lines

If this works, the monied and in-power will make this as illegal as LSD and heroin.

Not necessarily.

If the anti-aging drug(s) make people healthier, reducing the drain on the government pensions and enabling the government to push the retirement age out over the horizon, so the people will be working and taxed, they might prefer to have the drugs put into use.

Heck, they'd probably add them to the water.

Comment: Re:Twenty five years of science destruction... (Score 1) 118

Maybe you're right. Hey, did you see this?. For all we know, the reasonable budgets of a national space program with a Moon mission are a bargain for the new technology this mission might discover, and someday provide to prevent mass population die-offs due to poverty. But I really doubt it and I can't agree. India's space program is a bad idea considering they have such severe national problems. If the US in the 1960's was half as bad as India is today, the Moon missions would probably not have happened, even if Russia's program was putting pressure on US dominating races to every possible technical achievement. First feed your kids, istartedi... THEN you can go to the Moon.

Comment: Re:You know what would REALLY motivate kids? (Score 1) 203

You are clinging to your misconception about what CS is by arguing something entirely new: there are no CS "jobs." You are mistaken, btw. And what we are talking about is not a negligible chunk of change, as outside academia the starting salary of a B.S. computer scientist with zero experience is close to $70-80K these days, while I think you know any software developer graduating with any degree with zero experience won't touch that. Your ignorance of any positions for an actual, bone fide "computer scientist" is not a good foundation to argue from, IMO.

My point really simply was (sorry for the feigned ignorance) that maybe the Clinton Foundation, certainly Slashdot editors, and obviously you, mistakenly believe that the purpose of "Computer Science" in society in practice, is to fill the jobs for software developers. This is absurd on its face, and your academia-vs-real-world strawman does not change this.

Please refrain from limiting computer scientists to the labor of developers. All developers can do is code. Computer scientists have a much larger bag.

Comment: Re:Amazing (Score 1) 203

they're going for more people being able to understand CS and possibly do CS

Do you really think that not teaching a subject to kids will get more of them to learn it?

I truly believe they have misnamed the subject in question, and couldn't possibly be talking about CS, but perhaps skills, incidentally related, often attributed to CS incorrectly. IT WOULD BE AWESOME if some CS got into lower education. It shouldn't be expensive... no PCs necessary. But symbolic logic corses would be just as useful. Again, I don't think this is their (Clinton Foundation's) intention, but (perhaps slashdot editors) are misusing CS to mean either programming or confident graphic interface operation and document creation, or both. It is maddening the damage Slashdot has done to Computer Science, relegating it to "the stuff you can do with computers," instead of what it is, the science of computating.

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