If you hook 120V AC to a four-diode rectifier bridge, and hook the rectifier bridge to a suitable capacitor, and hook a voltmeter to that capacitor, you will measure 120*2*sqrt(2)=339.4V DC. If you power it from 240V AC, you get 678.8V DC, and while SCRs are commonly available for such voltages, designers will use an SCR on each leg to keep the negative output at ground potential.
I am not sure where the confusion is but this is not correct. A full wave bridge with a capacitor produces 170 volts DC from 120 volts AC. Maybe you were thinking of 240 volt AC with a neutral?
There are lots of ways to design power supplies, and designers are free to use their own approaches, but that's probably the most common one. Most modern switching power supplies (ones without a 120/240 switch on the back) are rated to use any input voltage from 100 to 240V, without any hole in the middle of the range that would indicate a doubler being used.
I have not personally been burnt by this but you have to be careful. Some power supplies use a voltage doubler without an external switch and they will automatically choose between 120 or 240 volts but there is a range in the middle where they can fail. Unfortunately, they are often marked in such a way that it is not possible to discern if they have a hole in their input range or not.
I would think the opposite would be true - instead of merely adding some inductors to the input to keep current flowing, you'd have to use a boost regulator or a transformer to bump up the voltage. I doubt their initial AC to DC conversion uses 120V AC - commercial power is typically delivered to office buildings as 480Y/277V 3-phase, and they probably take it straight from there.
For 120 and 240 volt AC inputs they tend to use a non isolated boost converter which requires the output voltage equal to or higher then the peak voltage. This makes an easy replacement for existing capacitor input rectifiers producing 340 volts DC. The ideal situation would be to use the building's 3 phase distribution but no obvious topology come to mind to produce 380 volts DC from it. Maybe they were rounding 392 volts down to 380 which is why I said I am not completely confident in the reported voltage. There are some clever 3 phase power factor correction designs but I do not have much experience with them.
If they used 48 volts instead of 380 volts the wiring would have to be 63 times thicker to handle the increased current with the same power loss. It is also easier to do the initial power factor corrected AC to DC conversion if the DC voltage is slightly higher then the peak AC voltage.
Standard line voltage computer power supplies are designed to run on 240 volts AC and rectify that to 340 volts DC internally. When they are powered by 120 volts AC, they use a voltage doubler to generate the 340 volts DC. Conceivably most would work fine on 340 volts DC without any changes but it depends on the details.
They did not say why they choose 380 volts DC but my guess is that either the article was mistaken and it was really 340 volts DC or using a voltage higher then the AC peak made for an easier initial AC to DC conversion when doing power factor correction.
Epoxy can be tricky to use which makes it a poor choice for this type of critical application. Mix it at the wrong temperature or with the wrong contaminates or apply it to the wrong type of surface and its strength can be greatly compromised without any visual indication.
In large structures, the strength that the materials are loaded to is often dictated by how large a progressive deformation or crack would have to be to be seen during inspection to give warning of future failure. Use a high enough stress, and your inspection will not catch the early signs of failure because they will be too small.
It sounds like the panels needed to have a low Q (ability to absorb energy while flexing in this case) to prevent vibration problems when used in a simple mechanical design. Concrete would be the obvious material but the high mass has now been shown to be a big problem given how it was anchored.
The panels themselves are needed seperate from the structural surface they are mounted on to provide an area for air circulation.
Ceramic capacitors are all piezoelectric to an extent with some types being much worse then others. Inductors and transformers can also become sound transducers depending on how they are constructed.
Normally neither of these sources would be an issue because all of the switching power supplies involved run at frequencies well above the audio range but some types can suffer from sub harmonic oscillation. This is normally an issue with current mode topologies that lack slope compensation but occasionally it shows up in other designs.
The flaw is even worse than you think, because it can't be remedied through "proper" voting. No matter what your political affiliation, you have no choice but re-electing a caste of professional politicians, which differ only on superficial and relatively inconsequential issues like a constitutional amendment explicitly banning gay flag-burning.
Vote for minor party? Only if you want to throw away your vote, for the complete lack of enforcement of gerrymandering laws means even the most incompetent of incumbents win over 90% of the time.
Game theory still convinces me that the solution to this is approval voting for single office holders and the equivalent in places where proportional representation is appropriate. I have to qualify this however because I have not been able to prove to myself that this sort of cure is better than the disease. I am cynical enough that I have difficulty believing in any sort of good government. Perhaps occasional gridlock is the best that can be hoped for.
Spread the word? Anything you say can be countered by a bombardment of disinformation and distractions that prevent effective dissent. One would think that the alternative media/internet get around this, and it can--but they're going to change that. Plans for complete regulation of the internet are already in the works under the guise of "tiered-service". As John Devorak says, we're in the golden age of the internet--enjoy it while it lasts, because it's soon to end.
I do not believe regulation of the internet is necessary or even enough. In the same way that bad money displaces good money, the same happens with discussion even without overt censorship. Public key encryption would seem to be the deciding factor here because it allows authentication but unless used, it becomes irrelevant. The only serious evidence I have for the government blocking its adoption is by not encouraging it. Maybe ignoring it is all that is required. It could also be the case that no serious opposition has arisen because it has not been widely adopted. Why attract attention so something that is going your way?
It kills me that the people that set up our government 200+ years ago did it mostly right, but since WWII the federal government here has gotten completely (and unconstitutionally) out of hand.
I would argue it got out of hand before then but that is a difference of degree and not of kind. In retrospect, baring the unpredictable, I do not see how it could have been any different given where we started 240 years ago and what we know now.
Has there ever been a revolution that just reinstated what was already there? Or does it always start with a clean slate?
Every successful revolution that I am aware of attempted (or at least promised) to correct injustices implying that they all started on a foundation based in some way on the previous order. It is very difficult to see outside of ones experience even if it is consciously attempted.
Clients tend to be overpowered for HTTP anyway so using HTTPS is not really noticeable unless you have really low performance hardware.
Servers are more likely to be used to capacity so HTTPS can be a much larger factor. The one place where I have found it really noticeable is with embedded hardware that supports HTTP and HTTPS access for web configuration. m0n0wall and pfsense among other open source projects support both and the performance difference can be large enough to make HTTPS painful to use at the low end. I have never tested it on modern server class hardware but I would guess it can affect performance by 3 to 4 times which would be unnoticeable on a lightly loaded server.
Unfortunately at 2.4GHz if you want to remotely mount an antenna for better performance it takes a little more then just removing it to add an extension. The small diameter coaxial cable they use which is similar to RG-174 has about 3db of loss per 5 feet. RG-58 does better at 12 feet per 3db but any extension quickly gives diminishing returns. Satellite receivers use a preamplifier build into the antenna to make up for their line losses.
The patent office only checks selected published material for prior art so lots of it gets missed. This is especially bad for software because usually the source code is not openly published making it impossible to review. In theory open source should solve that particular issue but I am not aware that the patent office is even aware of it at a level where it would matter.
The part that always bothered me about this policy is that it shows just how fragile modern planes are to electromagnetic interference. Should not the planes be designed and built to withstand the largest credible threat in at least a way that prevents the possibility of any sort of fatal crash?
What happens when the rules about operating non intentional radiators are ignored by someone who deliberately powers up a wide band jammer or something even more sophisticated that is specifically designed to severely interfere with the operation of the plane?
I had a friend who though the same thing reguarding his car. He figured replacing his belt driven water pump with an electric one powered by the alternator would save him the horse power needed to drive the original pump because power taken from the alternator was "free".
Unfortunately, it does not work that way. Placing a load on a generator or alternator makes it more difficult to turn and there are real forces involved. In the case of a plane, the power taken by 100 passangers using 75 watts each for a total of 7500 watts is tiny compaired to the output of a jet engine which is going to be rated in thousands of kilowatts.
Designing a system such that no possible fault on the passanger power bus can affect the rest of the aircraft is not particularly difficult.
I do not mean to denigrate cashiers as most are fine people in a tough job situation when I say that any system that relies on them to do any security related task other then obey the transaction computer or count cash (and maybe not even that) is bound to fail simply because the cost of a security related failure is so low compared to the cost of human driven security.
shouldn't the issue then be that the school year in the US needs to be re-examined so that you don't have the holidays all lumped at once
Some areas have done this and switched to a continuous school year. My understanding is that the long summer vacations originated from the need to allow children time off to help on family farms. I can imagine a debate about the merits of both systems in the distant past being decided by the fact that the rural children would have been kept home in summer to help no matter what school year schedule was used. The farmers would have had too much to lose and the state's interest in universal schooling would have encouraged a compromise leading to a practical if suboptimal solution. I would guess it was applied equally to urban and rural schools for the sake of uniformity.
Keep in mind that while states like California are known for high technology, their agricultural output is considerable. In the specific case of California, huge would not be an exaggeration. You only have to look at how water is managed to gage the political power involved. Between a growing urban population and fewer small farmers summer vacation is certainly not as important as it used to be but like a lot of government enforced institutions, inertia leads to solving the problems of the past.
Personally I think the problem is how the mechanics of the U.S. political system lead to poor and inflexable policy but that is a different discussion.
They really do exist but consider the context. The camps they are talking about are for urban grade school children who would be unlikely to work anyway during the 3 months of summer vacation and are considered too young to supervise themselves while their parents work. They spend 1 or 2 weeks in small groups sorted by age and gender living in a cabin with a counselor who is young enough for them to identify with and not be what they would consider an adult. The movie Meatballs was actually pretty close to what I remember if exaggerated. The best time I had was the year several members of my cabin were gamers and we played D&D every day.
Modern 3.5" hard drives are quiet enough that I do not notice them anyway. Although they are a little larger then needed, I like the half height enclosures from www.american-media.com. They have internal power supplies, stack flat, and do to the relatively large size provide good cooling and easy maintanance. The 5.25" ones also have a pass through standard AC power socket on the back.
No doubt added power conditioning could be included on the controller board that connects between the USB and the hard drive but I have not seen any that bother. There is not much room for a large capacitor in a 2.5" form factor enclosure.
That spare "power only" USB connector is suggestive about the USB power issue. Mine has a similar auxilary power cable but uses the PS/2 port. I have not lost any data either using mine but I would never rely on them for anything except temporary storage and transfer.
All of the USB 2.5" drives I have tested have been unreliable when powered using USB 5 volt power. USB only supports 5 volts at 0.5 amps which is marginal for directly powering a 2.5" drive. When they are externally powered, they have worked better but dealing with an external power brick for every drive is annoying.
Firewire should not have the power issues but drive cases with the necessary internal power conditioning are rare to nonexistent. They would need a small internal regulator for converting 12 to 36 volts from Firewire to 5 volts which is not difficult at all but my guess is it is not economically competitive with using an external brick power supply. The best solution I have found so far are the 3.5" half height and full height cases that have internal switching power supplies and use a standard computer AC power cable.
All of the systems I have used since USB2 became standard support booting from USB however I have never gotten it to work on anything except BSD or Linux. Windows XP tries but blue screens even if I go through heroic efforts to install it.
Slashdot Mirror
If you hook 120V AC to a four-diode rectifier bridge, and hook the rectifier bridge to a suitable capacitor, and hook a voltmeter to that capacitor, you will measure 120*2*sqrt(2)=339.4V DC. If you power it from 240V AC, you get 678.8V DC, and while SCRs are commonly available for such voltages, designers will use an SCR on each leg to keep the negative output at ground potential.
I am not sure where the confusion is but this is not correct. A full wave bridge with a capacitor produces 170 volts DC from 120 volts AC. Maybe you were thinking of 240 volt AC with a neutral?
There are lots of ways to design power supplies, and designers are free to use their own approaches, but that's probably the most common one. Most modern switching power supplies (ones without a 120/240 switch on the back) are rated to use any input voltage from 100 to 240V, without any hole in the middle of the range that would indicate a doubler being used.
I have not personally been burnt by this but you have to be careful. Some power supplies use a voltage doubler without an external switch and they will automatically choose between 120 or 240 volts but there is a range in the middle where they can fail. Unfortunately, they are often marked in such a way that it is not possible to discern if they have a hole in their input range or not.
I would think the opposite would be true - instead of merely adding some inductors to the input to keep current flowing, you'd have to use a boost regulator or a transformer to bump up the voltage. I doubt their initial AC to DC conversion uses 120V AC - commercial power is typically delivered to office buildings as 480Y/277V 3-phase, and they probably take it straight from there.
For 120 and 240 volt AC inputs they tend to use a non isolated boost converter which requires the output voltage equal to or higher then the peak voltage. This makes an easy replacement for existing capacitor input rectifiers producing 340 volts DC. The ideal situation would be to use the building's 3 phase distribution but no obvious topology come to mind to produce 380 volts DC from it. Maybe they were rounding 392 volts down to 380 which is why I said I am not completely confident in the reported voltage. There are some clever 3 phase power factor correction designs but I do not have much experience with them.
If they used 48 volts instead of 380 volts the wiring would have to be 63 times thicker to handle the increased current with the same power loss. It is also easier to do the initial power factor corrected AC to DC conversion if the DC voltage is slightly higher then the peak AC voltage.
With a good design and implementation, a simple isolated step down converter should be able to get 95% efficiency.
Standard line voltage computer power supplies are designed to run on 240 volts AC and rectify that to 340 volts DC internally. When they are powered by 120 volts AC, they use a voltage doubler to generate the 340 volts DC. Conceivably most would work fine on 340 volts DC without any changes but it depends on the details.
They did not say why they choose 380 volts DC but my guess is that either the article was mistaken and it was really 340 volts DC or using a voltage higher then the AC peak made for an easier initial AC to DC conversion when doing power factor correction.
Epoxy can be tricky to use which makes it a poor choice for this type of critical application. Mix it at the wrong temperature or with the wrong contaminates or apply it to the wrong type of surface and its strength can be greatly compromised without any visual indication.
In large structures, the strength that the materials are loaded to is often dictated by how large a progressive deformation or crack would have to be to be seen during inspection to give warning of future failure. Use a high enough stress, and your inspection will not catch the early signs of failure because they will be too small.
It sounds like the panels needed to have a low Q (ability to absorb energy while flexing in this case) to prevent vibration problems when used in a simple mechanical design. Concrete would be the obvious material but the high mass has now been shown to be a big problem given how it was anchored.
The panels themselves are needed seperate from the structural surface they are mounted on to provide an area for air circulation.
Ceramic capacitors are all piezoelectric to an extent with some types being much worse then others. Inductors and transformers can also become sound transducers depending on how they are constructed.
Normally neither of these sources would be an issue because all of the switching power supplies involved run at frequencies well above the audio range but some types can suffer from sub harmonic oscillation. This is normally an issue with current mode topologies that lack slope compensation but occasionally it shows up in other designs.
The Wikipedia article is accurate if brief:
http://en.wikipedia.org/wiki/V-chip
I have never actually seen it used but mostly because I do not know anyone's children who watches broadcast TV except for cartoons.
The flaw is even worse than you think, because it can't be remedied through "proper" voting. No matter what your political affiliation, you have no choice but re-electing a caste of professional politicians, which differ only on superficial and relatively inconsequential issues like a constitutional amendment explicitly banning gay flag-burning.
Vote for minor party? Only if you want to throw away your vote, for the complete lack of enforcement of gerrymandering laws means even the most incompetent of incumbents win over 90% of the time.
Game theory still convinces me that the solution to this is approval voting for single office holders and the equivalent in places where proportional representation is appropriate. I have to qualify this however because I have not been able to prove to myself that this sort of cure is better than the disease. I am cynical enough that I have difficulty believing in any sort of good government. Perhaps occasional gridlock is the best that can be hoped for.
Spread the word? Anything you say can be countered by a bombardment of disinformation and distractions that prevent effective dissent. One would think that the alternative media/internet get around this, and it can--but they're going to change that. Plans for complete regulation of the internet are already in the works under the guise of "tiered-service". As John Devorak says, we're in the golden age of the internet--enjoy it while it lasts, because it's soon to end.
I do not believe regulation of the internet is necessary or even enough. In the same way that bad money displaces good money, the same happens with discussion even without overt censorship. Public key encryption would seem to be the deciding factor here because it allows authentication but unless used, it becomes irrelevant. The only serious evidence I have for the government blocking its adoption is by not encouraging it. Maybe ignoring it is all that is required. It could also be the case that no serious opposition has arisen because it has not been widely adopted. Why attract attention so something that is going your way?
It kills me that the people that set up our government 200+ years ago did it mostly right, but since WWII the federal government here has gotten completely (and unconstitutionally) out of hand.
I would argue it got out of hand before then but that is a difference of degree and not of kind. In retrospect, baring the unpredictable, I do not see how it could have been any different given where we started 240 years ago and what we know now.
Has there ever been a revolution that just reinstated what was already there? Or does it always start with a clean slate?
Every successful revolution that I am aware of attempted (or at least promised) to correct injustices implying that they all started on a foundation based in some way on the previous order. It is very difficult to see outside of ones experience even if it is consciously attempted.
Clients tend to be overpowered for HTTP anyway so using HTTPS is not really noticeable unless you have really low performance hardware.
Servers are more likely to be used to capacity so HTTPS can be a much larger factor. The one place where I have found it really noticeable is with embedded hardware that supports HTTP and HTTPS access for web configuration. m0n0wall and pfsense among other open source projects support both and the performance difference can be large enough to make HTTPS painful to use at the low end. I have never tested it on modern server class hardware but I would guess it can affect performance by 3 to 4 times which would be unnoticeable on a lightly loaded server.
Unfortunately at 2.4GHz if you want to remotely mount an antenna for better performance it takes a little more then just removing it to add an extension. The small diameter coaxial cable they use which is similar to RG-174 has about 3db of loss per 5 feet. RG-58 does better at 12 feet per 3db but any extension quickly gives diminishing returns. Satellite receivers use a preamplifier build into the antenna to make up for their line losses.
What's your point?
The patent office only checks selected published material for prior art so lots of it gets missed. This is especially bad for software because usually the source code is not openly published making it impossible to review. In theory open source should solve that particular issue but I am not aware that the patent office is even aware of it at a level where it would matter.
The part that always bothered me about this policy is that it shows just how fragile modern planes are to electromagnetic interference. Should not the planes be designed and built to withstand the largest credible threat in at least a way that prevents the possibility of any sort of fatal crash?
What happens when the rules about operating non intentional radiators are ignored by someone who deliberately powers up a wide band jammer or something even more sophisticated that is specifically designed to severely interfere with the operation of the plane?
I had a friend who though the same thing reguarding his car. He figured replacing his belt driven water pump with an electric one powered by the alternator would save him the horse power needed to drive the original pump because power taken from the alternator was "free".
Unfortunately, it does not work that way. Placing a load on a generator or alternator makes it more difficult to turn and there are real forces involved. In the case of a plane, the power taken by 100 passangers using 75 watts each for a total of 7500 watts is tiny compaired to the output of a jet engine which is going to be rated in thousands of kilowatts.
Designing a system such that no possible fault on the passanger power bus can affect the rest of the aircraft is not particularly difficult.
I do not mean to denigrate cashiers as most are fine people in a tough job situation when I say that any system that relies on them to do any security related task other then obey the transaction computer or count cash (and maybe not even that) is bound to fail simply because the cost of a security related failure is so low compared to the cost of human driven security.
Urban grade? Do they taste better or worse than so-called premium grade?
I am not aware of a premium grade. The rural grade is a little gamey for my taste.
I probably could have phrased my original post better to deal with the inevitable U.S. to U.K. translation.
shouldn't the issue then be that the school year in the US needs to be re-examined so that you don't have the holidays all lumped at once
Some areas have done this and switched to a continuous school year. My understanding is that the long summer vacations originated from the need to allow children time off to help on family farms. I can imagine a debate about the merits of both systems in the distant past being decided by the fact that the rural children would have been kept home in summer to help no matter what school year schedule was used. The farmers would have had too much to lose and the state's interest in universal schooling would have encouraged a compromise leading to a practical if suboptimal solution. I would guess it was applied equally to urban and rural schools for the sake of uniformity.
Keep in mind that while states like California are known for high technology, their agricultural output is considerable. In the specific case of California, huge would not be an exaggeration. You only have to look at how water is managed to gage the political power involved. Between a growing urban population and fewer small farmers summer vacation is certainly not as important as it used to be but like a lot of government enforced institutions, inertia leads to solving the problems of the past.
Personally I think the problem is how the mechanics of the U.S. political system lead to poor and inflexable policy but that is a different discussion.
They really do exist but consider the context. The camps they are talking about are for urban grade school children who would be unlikely to work anyway during the 3 months of summer vacation and are considered too young to supervise themselves while their parents work. They spend 1 or 2 weeks in small groups sorted by age and gender living in a cabin with a counselor who is young enough for them to identify with and not be what they would consider an adult. The movie Meatballs was actually pretty close to what I remember if exaggerated. The best time I had was the year several members of my cabin were gamers and we played D&D every day.
Modern 3.5" hard drives are quiet enough that I do not notice them anyway. Although they are a little larger then needed, I like the half height enclosures from www.american-media.com. They have internal power supplies, stack flat, and do to the relatively large size provide good cooling and easy maintanance. The 5.25" ones also have a pass through standard AC power socket on the back.
s /Venus_single.html
http://www.american-media.com/Products/VenusSerie
No doubt added power conditioning could be included on the controller board that connects between the USB and the hard drive but I have not seen any that bother. There is not much room for a large capacitor in a 2.5" form factor enclosure.
That spare "power only" USB connector is suggestive about the USB power issue. Mine has a similar auxilary power cable but uses the PS/2 port. I have not lost any data either using mine but I would never rely on them for anything except temporary storage and transfer.
All of the USB 2.5" drives I have tested have been unreliable when powered using USB 5 volt power. USB only supports 5 volts at 0.5 amps which is marginal for directly powering a 2.5" drive. When they are externally powered, they have worked better but dealing with an external power brick for every drive is annoying.
Firewire should not have the power issues but drive cases with the necessary internal power conditioning are rare to nonexistent. They would need a small internal regulator for converting 12 to 36 volts from Firewire to 5 volts which is not difficult at all but my guess is it is not economically competitive with using an external brick power supply. The best solution I have found so far are the 3.5" half height and full height cases that have internal switching power supplies and use a standard computer AC power cable.
All of the systems I have used since USB2 became standard support booting from USB however I have never gotten it to work on anything except BSD or Linux. Windows XP tries but blue screens even if I go through heroic efforts to install it.