Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!

 



Forgot your password?
typodupeerror

Comment Re:50% is lost in AC to DC conversion? (Score 1) 357

I once had a car lighter socket to USB power adapter that started to flake out on me. When I opened it I found ten diodes in series. That was the whole show. Turned out the "problem" was my car battery was about to die, which was why the "power adapter" was not producing 5 volts anymore...

Comment Re:It's nice to have ideals (Score 1) 357

Lets be honest, if Toyota were any good at building the electric part of a hybrid, they would be building the cars that tesla is building. There is a reason Tesla motors is king of the electrics and everyone else is playing second fiddle. You wont find an AC induction motor powering a teal any time soon. The only advantage that Induction motors have is that they are cheaper to build than DC brushless. That is the only real advantage. They are harder to control, have worse efficiency, the control electronics costs more. It is not at all surprising to me that an established auto company is doing things all crabbed when it comes to electric vehicles. They are still functionally retarded when it comes to electronics.

Comment Re:DC is more dangerous (Score 1) 357

AC has one significant advantage in that it generates much less heat on the wire, and the higher voltages, within reason, allow for smaller wires to do the same work, as wire size need is a function of amps.

That advantage is not intrinsic to AC vs DC, it is a result of the voltage involved. The transmission losses of a DC system running at 120V is pretty much the same as the losses from an AC system running at 120V. (I know that power factor and all that, but with more and more AC to DC converters pulling power from the AC lines, the power factors are getting royally borked anyways) In many ways DC has an actual advantage. AC transmission lines have a capacitance associated with them. This causes additional losses on the transmission lines that do not occur with DC. (Think of it this way: The line has a giant capacitor on it, and an AC source has to charge and then discharge that capacitor 60 times a second. With DC, the capacitor gets charged and stays charged.) This means that the *effective* resistance of a DC transmission line is lower than the same exact line transmitting AC power.

Comment Re:DC is more dangerous (Score 1) 357

the decision to use AC over DC was not random nor taken lightly, there are many factors involved (heck, it was a major engineering, corporate, and PR war between Edison and Westinghouse: https://en.wikipedia.org/wiki/... [wikipedia.org] ), but the right decision was made

The right decision was made for the time. At that time, no one could have envisioned modern electronics. The advent of the transistor marked the turning point at which DC power would eventually become the better option. It was just a matter of time after that until control electronics got good enough and efficient enough to make DC a better option. We are almost at that point now. DC power line transmission is a better alternative if one assumes that the technology exists to do voltage conversion at high voltages (its not currently there yet, but at the current rate of technological improvement, we will be there in 20 or so years). The conversion to DC is not even something that will need to be done all at once. Individual long haul lines can be converted one at a time until the power form the power company is HVDC all the way to you local transformer. At that point, it will make sense for the power company to offer a HVDC feed for those that want it. This would be advantageous for solar and wind installations because interfacing with these power system would not require complex and expensive phase matching equipment. It would be advantageous for those that have mostly DC appliances because they would save 10% on their electricity costs because they would no longer have to pay the 5% efficiency loss to convert to AC power at the pole, and they would save an additional 5% by not having to convert from AC back to DC inside the appliance. For power utilities it would be cheaper because of less transmission losses as well as less risk of power line phase issues causing transmission line faults and unexpected drop outs. We are still many decades away from HVDC power becoming a reality, but it will come. It will happen because it can happen and the advantages will eventually outweigh the cost of retrofit.

Comment Re:Stone Age... (Score 1) 357

an ac synchronous motor is much more efficient than DC alternatives.

Not any more. 30 years ago that was true, but DC brushless motors have seen a great deal of improvement in the last three decades. High power and high efficiency are pretty normal in DC induction and DC PM motors these days. The biggest contributing factor has been orders of magnitude improvements in power electronics (where most of the efficiency losses used to be). It is not uncommon to find motor / control electronics packages now that are pushing 95% efficient up to tens (or even hundreds) of horsepower. (Thats tens to hundreds of kilowatts for those of you who are so inclined).

Comment Re:He wasn't able to give it up. (Score 1) 357

HVAC uses 3-phase AC power which is actually pretty efficient for motors, especially if you want motors that are going to last a long time.

No, no it doesnt. Commerical and residential HVAC is almost all 240VAC (two phases 180 degrees out of phase). Only industrial HVAC is 3 phase, as 3 phase is generally only needed / installed in an industrial setting.

Pretty much all brushless motors are driven by AC

Again, no they aren't. A very large portion of brushless motors including those used in large appliances, automotive (drivetrain and otherwise), computers, etc... are AC/DC brushless motors that will function on any power source. There are plenty of DC brushless motors and AC/DC brushless motors available that are equal in efficiency, longevity and power to their AC only cousins.

3-phase is great for motors that run at a single RPM, such as what is used in compressors and pumps for HVAC.

This is probably the closest to correct you have been. For commercial and residential power, 2 phase AC motors have traditionally been used, but they are largely inefficient in their use of power compared to modern options because it is difficult to operate a fixed speed heat pump efficiently under a varying load. More recently, we are beginning to see modulating heat pumps that offer a variable power setting. These require the use of PWM drive DC motors, or expensive / inefficient AC inverters to drive the pump motors. These modulating systems are almost ideal for operation from DC sources like solar and wind drive because they can be designed to function directly from the DC feed without the need for DC to AC conversion, visa-versa, or both. They consequently have the lowest operating losses, transmission losses and conversion losses of any available options.

disclaimer: I work for an HVAC controls company

Comment Re:And it all comes down to greed (Score 2) 568

And the fact that "total wages and salaries last year amounted to $7.1 trillion, or 42.5 percent of the entire economy [...] lower than in any year previously measured" is also hardly surprising: given that the US government keeps on piling mandates on employers, employers are satisfying those mandates in lieu of raises.

Thats just plain crap. Regulation does not help wages nor hurt it. If that were the case, then deregulation of the airline industry would have increased wages for pilots and air crews. In reality wages for these groups have been declining just like everyone else. Deregulation of the utilities? Same effect, declining wages just like everything else. The reality is that regulation is the bogeyman that the wealthy have pushed to try to give the bottom 20% something other than corporate greed vis-a-vis capitalism to rail against. In effect, its a giant con. They dont actually expect to eliminate regulation, but on the off chance that they do succeed and regulation is reduced, it simply allows corporations to gain greater profits by sacrificing health and safety for employees and the general public: a double win for the rich and powerful.

Comment Re:And it all comes down to greed (Score 1) 568

That would be wonderful: all basic human needs met without any backbreaking work. You really have to be quite misanthropic to think that that is a bad thing.

It's not a bad thing. The bad comes from what humanity will do when it reaches that stage. Instead of sharing the freedom and wealth that this state of affairs will bring, a small percentage of the population will benefit from it and capitalism will work to effectively exclude the vast majority of the population. These excluded souls will be pushed to extinction and will either fight back or die.

Comment Re:File this under duh (Score 2) 568

Overall, people today have more job security than in the past, not less.

75% of American jobs are in the service sector. The vast majority of these job are jobs that no one wants, even the people filling them currently. Surety of keeping a crappy job is not job security, its indentured servitude. It may not carry the same contract, but in point of fact it is the same thing.

Comment Re:Nope... (Score 1) 511

Flying through the air above your property is not criminal trespass. What's your next guess?

If youd had read the link, you would have noticed that there is precedent for trespass to include a certain amount of the airspace above the property. Where the line is drawn is usually a function of what the trespasser was doing there in the first place.

Comment Re:What? (Score 1) 184

As an old tyme Windows hater, I'm not getting some of this. On the 29th I reserved my upgrade.

Huh? I find it unlikely that anyone who described themselves as a windows hater would upgrade to the latest version of the OS, much less on release day. You can turn in your card at the main office...

Comment Re: Windows sounds easier to update than Debian. (Score 0) 184

"Victim" is the right word.

I was under the impression that SystemD wasn't yet in the stable releases, and was still just in the advanced releases. I'm 100% certain this is true for Ubuntu, as the 14.04 LTS still uses upstart.

If it is in the stable releases, then some of the maintainers need to be shot for letting unstable components into the stable releases. If it is still just in the advance releases, then why are people complaining when all the bugs haven't been worked out? Thats the whole point of advanced releases... If you insist on being on the bleeding edge, then you're going to bleed.

All I know for certain at this point is that when SystemD has some maturity behind it, I *will* switch to it; probably when the next Ubuntu LTS is released with it turned on.

"Well, it don't make the sun shine, but at least it don't deepen the shit." -- Straiter Empy, in _Riddley_Walker_ by Russell Hoban

Working...