Buy 2-3 APC UPSes, each 700VA or so [...] Wire one car battery to each UPS
I think this is asking for a fried UPS. Most UPS's of that size are designed for batteries of a specific capacity - their chargers and inverters are only designed to run for certain lengths of time.
To be safe, get a UPS designed to accept additional external battery packs, and don't attach (much) more capacity to it than the manufacturer allowed for.
And PLEASE don't use car batteries! You'd kill them dead in just a few full cycles! Only use deep cycle batteries.
Sandia's web site doesn't say what their cost per megawatt hour is
But this Department of Energy page does. They say such systems are currently at 9-12 cents/kWh, but expect 4-5 cents/kWh in a few decades. Which is certainly competitive.
Photoelectric won't work, won't solve even a small fraction of our power needs, not remotely.
Don't confuse photoelectrics with photovoltaics.
For example, Sandia Labs has a plant currently in operation that produces 5MW in 9 acres, by focusing light onto a tower that heats molten salt which drives turbines. It can produce energy 24 hours a day.
The United States' generating capacity a few years ago was 813 gigawatts, so at.55 MW per acre you'd need 1.4 million acres for all of the US's energy needs. That's about 2300 square miles or 6000 square kilometers, or about 1.5 Rhode Islands. We have many deserts that are larger than that.
Realistically, you don't need a power generation mechanism to be able to handle the entire United States energy needs before you put it in production. You just need it to be cheap (and cheap after the costs of fighting NIMBY lawsuits are factored in).
Sandia's web site doesn't say what their cost per megawatt hour is, but they do say the entire facility is currently worth $120 million. Since this type of system uses nothing exotic, I would expect economies of scale to change the numbers quite a bit. Assuming a life of 30 years, they'd have to be able to reduce the cost by about a factor of 10 to be competitive with today's rates. It could happen.
On a similar note - can anyone explain why the key to my car will lock and unlock the car at significantly greater distances if I hold it up to the side of my head (the key, not the car)?
Most key fobs operate with an electrically short antenna so that it can fit in your pocket. (for example, mine uses 433MHz but its loop antenna has a circumference of only a few centimeters. A proper loop antenna for 433MHz would be 70 centimeters long).
The performance of electrically short antennas can often be enhanced by adding capacitance to the antenna. Your body, even though it is not electrically in contact, is close enough to the antenna to be a little bit capacitatively coupled to it. The antenna is more resonant, more power is radiated, and your key fob works a little bit further away.
Same thing happens when you're adjusting the bunny ears on your TV. Chances are, the antenna is very poorly matched to the frequency you're trying to receive, because there are a lot of frequencies and only one antenna. Your body's capacitance helps reduce this mismatch, and as long as you stand right there and hold it just like you were doing a second ago, no, a little to the left your friends can enjoy the show.
We can see lightyears and lightyears away with Hubble, and other large telescopes. So how is it were still finding moons in the solar system?
Because we can only see light (well, electromagnetic radiation, to be more precise). While stars give off incredible amounts of light, moons only (poorly) reflect the light from those stars.
I suppose that's why they're lacking a fancy lumen number to throw around: because LEDs, as highly directional light sources, are measured in Candles (abbreviated "cd" or millicandles as "mcd") and not measured in Lumens.
LED's do isotropically radiate. It's just that a lot of them have mirrors and/or lenses molded in with the diode (much like a flashlight has a reflector around the incandescant bulb) to be directional.
Not to detract from your point about lumens vs. candelas, but with either system there is a certain amount of light radiated in all directions before the optics focus it. Whatever logic applies to defining the specifications for one applies to the other as well.
Basically, you need a certain signal to noise ratio for a digital radio connection to work at all at its lowest speed. Increased signal to noise ratios get you more speed and some margin of reliability.
Signal decreases with the square of the distance. If you double the distance you'll have one quarter the signal, or 6db less (decibels are logarithmic - 3db is a ratio of 2, 10db is a ratio of 10). So, everything else being equal, you'd need 6db more gain on the antenna at either end to get the same results.
For your particular scenario you'd probably be fine with just a couple cantennas or other moderate-gain antennas.
One thing to watch out for when shooting through trees is that they may not have leaves now but they will in a few months!
I can also hook a 9V battery to a 10kohm resistor dunked in a cup of water and the cup of water won't get noticably warmer either.
I can't find any references on the web to electrolysis systems currently operating with greater than 75% efficiency. Most of the numbers I see are 65%.
For car usage, you also have to deal with the efficiency of the engine or fuel cell you're using. Either way you're limited to the Carnot efficiencies of the temperature differences utilizied. 50% efficiency may be an optimistic figure.
50%*65% = 32%
Compare that to NiMH batteries, which will give you 66% of the energy you put into them. They'll drive electric motors which are easily 90% efficient.
66%*90% = 59%
Granted, if you're of the notion that nuclear fusion will make energy so cheap that you won't care about those numbers, high-pressure hydrogen tanks have energy densities of 500-1000 watt hours/kilogram, as opposed to NiMH's 70 wh/kg. (Compare either with gasoline at 12000 wh/kg). This is at least partially offset by the relative weights of electric motors vs. engines.
Personally, I like the idea of using the sun and otherwise-unusable desert to farm a lot of high-oil-content algae, then pumping the biodiesel from that into our car engines.
There is a relationship between the size of the holes and the wavelengths that seep through so if you know which wavelengths you want to keep out, you can tailor your cage to match your requirements.
For those following along at home, you can use Google Calculator to help you with this.
1/10th wavelength is a generally accepted mesh size for blocking RF. You can be more paranoid if you want (for example the holes in your microwave oven door are about 1/50th wavelength).
To calculate 1/10th of a wavelength at 2.45GHz, type "c/2.45GHz/10" into Google. Bam, 1.22 centimeters. Anything conductive with holes no larger than that will function as a faraday cage for RF up to that frequency (and will probably significantly attenuate RF in higher frequencies as well).
So it is not in the best interests of the US society, or at least it's overlords, to teach people basic economy (or to be critical of commercials, or anything else that would make them harder to exploit).
No, but it is in the interests of the local community, of which the teachers are members.
Ask a teacher sometime what they're proud of - what has given them their greatest sense of accomplishment - and when they answer, consider taking them at their word.
I think I remember reading that about half of the revenue that the IRS takes in is used in IRS overhead.
If that were true, the IRS's overhead would be almost one trillion dollars for 2004.
Searching google for "united states budget" pulls up the Office of Management and Budget page. Clicking on the budget for 2005 and then "Department of the Treasury" reveals the Internal Revenue Service's overhead was more like $10 billion, or about $45 per tax return.
Compare that to the Department of Defense's $433 billion outlay for 2004 or Social Security's $492 billion.
BPL sends a radio signal not over the transmission wire, but inside the electro magnetic field surrounding a high voltage line, similar to how a light bounces inside of a FiberOptic Cable.
Clue: All signals are waves. (Fourier)
Clue #2: All electrical signals are electromagnetic waves. (Ampere)
Clue #3: Electromagnetic waves are not contained in fields, they are the fields and the fact that that energy has formed a field means that it is no longer in the wire. (Faraday)
Clue #4: To keep these waves from forming fields of radiation, we can place an opposing (balanced) wave near it, twisting it occasionally (twisted pair), or we can place it in a faraday cage (coax).
Clue #5: Neither of these methods are used with power lines.
How much interference is released appears to be very debatable.
Clue #6: How much interference is released can be calculated, or observed through experimentation.
Clue #7: "Reality must take precedence over public relations, for nature cannot be fooled." (Feynman)
Cable modems (using coax), due to the nature of coax, the more up you send, the less down you can recieve. iirc it's more of a technology limitation than most other things.
No, it's a policy limitation. Because cable modems are connected with other cable modems in the same neighborhood, what they transmit is received by those other cable modems. Thus transmissions by cable modems must be limited to avoid interference with other things on the cable line, like downstream traffic to another user or TV channels. So the cable company dedicates a (usually smaller) chunk of bandwidth for these transmissions.
It has nothing to do with coax per se. Think about the other things that use coax - 10mbps ethernet, 45mbps T3's, 802.11 antenna feeds, etc.
If you pay $1000/year of heating by gas, you'll easily pay $2500/year for electric. That's a $1500 difference.
Or, in my experience, $800 for the total electric bill for the year with electric heating, and more like $400/yr for electric with gas heating and $150/yr for the gas bill.
Thermodynamics kick in again: it takes energy to move that heat around.
Not unless you need active circulation (such as a ceiling fan, which, come to think of it, I don't see people use much in winter). Entropy increases all by itself.
Your statement assumes that you use (inefficient) electric heat, and that your "energy wasting appliances" are nearly as efficient as your electric baseboard heating system.
Electric baseboard heating is 100% efficient. Every watt of energy put into a baseboard heater comes out as heat.
Similarly, every watt of energy put into a refrigerator comes out as heat. Likewise for your computer, entertainment system, washer/dryer, etc, etc. (although exceptions can be made for the hot water heater and dishwasher - a lot of that heat energy goes towards heating the sewer pipes.)
If your recessed ceiling lamps are decent at reflecting radiant heat (infrared light), a significant fraction of their heat output will go towards heating your room. If they aren't decent in such respects, why not use a little paint and make them so? They'll appear brighter as well.
You said you have recessed lighting and an attic above you... I'm guessing you don't live in an apartment. Why not fix the situation so that your attic insulation covers your recessed lighting too?
It's a shame how both of those links, especially the one about saving electricity in an apartment, fail to acknowledge the thermodynamics of the situation.
If you have electric resistance heating, and are using it, then most other changes simply will not have any effect. Any energy wasting appliances will simply cause your heater to turn on less often.
If you have natural gas heating, then by using energy-wasting appliances, you are choosing to use the more expensive electricity for part of your heating instead of gas. A pity, but not the end of the world.
During the winter, your methods of saving electricity are limited to allowing lower temperatures inside and finding ways to prevent heat loss to the outside (such as the suggested curtains).
Now, during the summer, when your apartment stays plenty warm on its own, all of this electricity is going to waste. In fact, for every watt you waste, you will spend another fraction of a watt moving that heat out of your apartment with a fan or with air conditioning.
Yes, and very nearly only human-readable. One gets the impression that METAR data is designed to be printed in a list so a pilot can review the weather on his flight path.
Here's an example of METAR data for Boeing Field, Seattle:
KBFI 060253Z 15007KT 10SM OVC017 05/02 A2967 RMK AO2 SLP045
T00500022 58003
It looks like a space-delimited flat file, but it's really not. METAR does not have a fixed number of fields (some columns only appear under certain weather conditions or may appear more than once, for example gusting conditions or multiple cloud cover ceilings). Sometimes you have to resort to looking at the next field to figure out through a process of elimination what the current field is.
Government documentation to explain how to read METAR data is several pages long. Code to fully parse it is similarly long, and I'm looking forward to retiring it.
Just a question, does anyone know how is light intensity measured? I've heard of a unit called a "lumin" or something like that. Is this the "output" that they are measuring? I was under the impression that a 100W bulb will consume 100W of electrical power, and depending on the efficiency of the bulb, you will get less than 100W of radiated power.
Yes, but it's spelled "lumen" (strictly speaking, output is measured in lumen, intensity upon an illuminated surface is measured in lux). A theoretical 100%-efficient lightbulb will convert 1 watt of electricity into 683 lumens, however no lightbulb approaches this. For example a 100 watt incandescent will typically output 1700 lumens for a 2.5% efficiency. The 14-watt compact flourescent bulbs I bought for $10/6 output 900 lumens for 9.4% efficiency. Enlux's neutral-white floodlight does 300 lumens with 15 watts input (no lumens data listed for their 22W nominal input) for 2.9% efficiency.
The best low-pressure sodium lamps do 183 lumens per watt, or 26.8% efficiency, however like many high-efficiency lamps they produce only a single output color, meaning that your eye won't be able to distinguish colors of objects illuminated solely by such a bulb. A lamp's ability for it to produce a natural variety of colors is measured by its CRI (Color Rendering Index).
Umm, last time I checked, the UN gave us permission when the Security Council passed resolution 1441.
"There's no 'automaticity' and this is a two-stage process, and in that regard we have met the principal concerns that have been expressed for the resolution. Whatever violation there is, or is judged to exist, will be dealt with in the council, and the council will have an opportunity to consider the matter before any other action is taken."
-- John Negroponte, US Ambassador, on UN Resolution 1441
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I think this is asking for a fried UPS. Most UPS's of that size are designed for batteries of a specific capacity - their chargers and inverters are only designed to run for certain lengths of time.
To be safe, get a UPS designed to accept additional external battery packs, and don't attach (much) more capacity to it than the manufacturer allowed for.
And PLEASE don't use car batteries! You'd kill them dead in just a few full cycles! Only use deep cycle batteries.
But this Department of Energy page does. They say such systems are currently at 9-12 cents/kWh, but expect 4-5 cents/kWh in a few decades. Which is certainly competitive.
Don't confuse photoelectrics with photovoltaics.
For example, Sandia Labs has a plant currently in operation that produces 5MW in 9 acres, by focusing light onto a tower that heats molten salt which drives turbines. It can produce energy 24 hours a day.
The United States' generating capacity a few years ago was 813 gigawatts, so at .55 MW per acre you'd need 1.4 million acres for all of the US's energy needs. That's about 2300 square miles or 6000 square kilometers, or about 1.5 Rhode Islands. We have many deserts that are larger than that.
Realistically, you don't need a power generation mechanism to be able to handle the entire United States energy needs before you put it in production. You just need it to be cheap (and cheap after the costs of fighting NIMBY lawsuits are factored in).
Sandia's web site doesn't say what their cost per megawatt hour is, but they do say the entire facility is currently worth $120 million. Since this type of system uses nothing exotic, I would expect economies of scale to change the numbers quite a bit. Assuming a life of 30 years, they'd have to be able to reduce the cost by about a factor of 10 to be competitive with today's rates. It could happen.
For copyright infringement, yes that's the case. However, you have to actually do trade with a trademark to maintain your claim to it.
Most key fobs operate with an electrically short antenna so that it can fit in your pocket. (for example, mine uses 433MHz but its loop antenna has a circumference of only a few centimeters. A proper loop antenna for 433MHz would be 70 centimeters long).
The performance of electrically short antennas can often be enhanced by adding capacitance to the antenna. Your body, even though it is not electrically in contact, is close enough to the antenna to be a little bit capacitatively coupled to it. The antenna is more resonant, more power is radiated, and your key fob works a little bit further away.
Same thing happens when you're adjusting the bunny ears on your TV. Chances are, the antenna is very poorly matched to the frequency you're trying to receive, because there are a lot of frequencies and only one antenna. Your body's capacitance helps reduce this mismatch, and as long as you stand right there and hold it just like you were doing a second ago, no, a little to the left your friends can enjoy the show.
Because we can only see light (well, electromagnetic radiation, to be more precise). While stars give off incredible amounts of light, moons only (poorly) reflect the light from those stars.
LED's do isotropically radiate. It's just that a lot of them have mirrors and/or lenses molded in with the diode (much like a flashlight has a reflector around the incandescant bulb) to be directional.
Not to detract from your point about lumens vs. candelas, but with either system there is a certain amount of light radiated in all directions before the optics focus it. Whatever logic applies to defining the specifications for one applies to the other as well.
DNS is not case sensitive. The filename portion of the URL is very much case sensitive.
(Even on a Windows web server with a case-insensitive filesystem, CGI scripts can distinguish uppercase vs. lowercase.)
Use a link budget calculator. (The link is one I just found with google).
Basically, you need a certain signal to noise ratio for a digital radio connection to work at all at its lowest speed. Increased signal to noise ratios get you more speed and some margin of reliability.
Signal decreases with the square of the distance. If you double the distance you'll have one quarter the signal, or 6db less (decibels are logarithmic - 3db is a ratio of 2, 10db is a ratio of 10). So, everything else being equal, you'd need 6db more gain on the antenna at either end to get the same results.
For your particular scenario you'd probably be fine with just a couple cantennas or other moderate-gain antennas.
One thing to watch out for when shooting through trees is that they may not have leaves now but they will in a few months!
I can also hook a 9V battery to a 10kohm resistor dunked in a cup of water and the cup of water won't get noticably warmer either.
I can't find any references on the web to electrolysis systems currently operating with greater than 75% efficiency. Most of the numbers I see are 65%.
For car usage, you also have to deal with the efficiency of the engine or fuel cell you're using. Either way you're limited to the Carnot efficiencies of the temperature differences utilizied. 50% efficiency may be an optimistic figure.
50%*65% = 32%
Compare that to NiMH batteries, which will give you 66% of the energy you put into them. They'll drive electric motors which are easily 90% efficient.
66%*90% = 59%
Granted, if you're of the notion that nuclear fusion will make energy so cheap that you won't care about those numbers, high-pressure hydrogen tanks have energy densities of 500-1000 watt hours/kilogram, as opposed to NiMH's 70 wh/kg. (Compare either with gasoline at 12000 wh/kg). This is at least partially offset by the relative weights of electric motors vs. engines.
Personally, I like the idea of using the sun and otherwise-unusable desert to farm a lot of high-oil-content algae, then pumping the biodiesel from that into our car engines.
For those following along at home, you can use Google Calculator to help you with this.
1/10th wavelength is a generally accepted mesh size for blocking RF. You can be more paranoid if you want (for example the holes in your microwave oven door are about 1/50th wavelength).
To calculate 1/10th of a wavelength at 2.45GHz, type "c/2.45GHz/10" into Google. Bam, 1.22 centimeters. Anything conductive with holes no larger than that will function as a faraday cage for RF up to that frequency (and will probably significantly attenuate RF in higher frequencies as well).
No, but it is in the interests of the local community, of which the teachers are members.
Ask a teacher sometime what they're proud of - what has given them their greatest sense of accomplishment - and when they answer, consider taking them at their word.
If that were true, the IRS's overhead would be almost one trillion dollars for 2004.
Searching google for "united states budget" pulls up the Office of Management and Budget page. Clicking on the budget for 2005 and then "Department of the Treasury" reveals the Internal Revenue Service's overhead was more like $10 billion, or about $45 per tax return.
Compare that to the Department of Defense's $433 billion outlay for 2004 or Social Security's $492 billion.
Clue: All signals are waves. (Fourier)
Clue #2: All electrical signals are electromagnetic waves. (Ampere)
Clue #3: Electromagnetic waves are not contained in fields, they are the fields and the fact that that energy has formed a field means that it is no longer in the wire. (Faraday)
Clue #4: To keep these waves from forming fields of radiation, we can place an opposing (balanced) wave near it, twisting it occasionally (twisted pair), or we can place it in a faraday cage (coax).
Clue #5: Neither of these methods are used with power lines.
How much interference is released appears to be very debatable.
Clue #6: How much interference is released can be calculated, or observed through experimentation.
Clue #7: "Reality must take precedence over public relations, for nature cannot be fooled." (Feynman)
No, it's a policy limitation. Because cable modems are connected with other cable modems in the same neighborhood, what they transmit is received by those other cable modems. Thus transmissions by cable modems must be limited to avoid interference with other things on the cable line, like downstream traffic to another user or TV channels. So the cable company dedicates a (usually smaller) chunk of bandwidth for these transmissions.
It has nothing to do with coax per se. Think about the other things that use coax - 10mbps ethernet, 45mbps T3's, 802.11 antenna feeds, etc.
No, that's agnosticism.
20 END
Can't come up with ten holes in this code? You fail.
Crap. With a Courier or Times font, I can't count more than nine. Can I change the line numbers?
Zigbee uses AES for authentication and encryption.
Or, in my experience, $800 for the total electric bill for the year with electric heating, and more like $400/yr for electric with gas heating and $150/yr for the gas bill.
Thermodynamics kick in again: it takes energy to move that heat around.
Not unless you need active circulation (such as a ceiling fan, which, come to think of it, I don't see people use much in winter). Entropy increases all by itself.
Electric baseboard heating is 100% efficient. Every watt of energy put into a baseboard heater comes out as heat.
Similarly, every watt of energy put into a refrigerator comes out as heat. Likewise for your computer, entertainment system, washer/dryer, etc, etc. (although exceptions can be made for the hot water heater and dishwasher - a lot of that heat energy goes towards heating the sewer pipes.)
If your recessed ceiling lamps are decent at reflecting radiant heat (infrared light), a significant fraction of their heat output will go towards heating your room. If they aren't decent in such respects, why not use a little paint and make them so? They'll appear brighter as well.
You said you have recessed lighting and an attic above you... I'm guessing you don't live in an apartment. Why not fix the situation so that your attic insulation covers your recessed lighting too?
If you have electric resistance heating, and are using it, then most other changes simply will not have any effect. Any energy wasting appliances will simply cause your heater to turn on less often.
If you have natural gas heating, then by using energy-wasting appliances, you are choosing to use the more expensive electricity for part of your heating instead of gas. A pity, but not the end of the world.
During the winter, your methods of saving electricity are limited to allowing lower temperatures inside and finding ways to prevent heat loss to the outside (such as the suggested curtains).
Now, during the summer, when your apartment stays plenty warm on its own, all of this electricity is going to waste. In fact, for every watt you waste, you will spend another fraction of a watt moving that heat out of your apartment with a fan or with air conditioning.
Yes, and very nearly only human-readable. One gets the impression that METAR data is designed to be printed in a list so a pilot can review the weather on his flight path.
Here's an example of METAR data for Boeing Field, Seattle:
KBFI 060253Z 15007KT 10SM OVC017 05/02 A2967 RMK AO2 SLP045 T00500022 58003
It looks like a space-delimited flat file, but it's really not. METAR does not have a fixed number of fields (some columns only appear under certain weather conditions or may appear more than once, for example gusting conditions or multiple cloud cover ceilings). Sometimes you have to resort to looking at the next field to figure out through a process of elimination what the current field is.
Government documentation to explain how to read METAR data is several pages long. Code to fully parse it is similarly long, and I'm looking forward to retiring it.
Yes, but it's spelled "lumen" (strictly speaking, output is measured in lumen, intensity upon an illuminated surface is measured in lux). A theoretical 100%-efficient lightbulb will convert 1 watt of electricity into 683 lumens, however no lightbulb approaches this. For example a 100 watt incandescent will typically output 1700 lumens for a 2.5% efficiency. The 14-watt compact flourescent bulbs I bought for $10/6 output 900 lumens for 9.4% efficiency. Enlux's neutral-white floodlight does 300 lumens with 15 watts input (no lumens data listed for their 22W nominal input) for 2.9% efficiency.
The best low-pressure sodium lamps do 183 lumens per watt, or 26.8% efficiency, however like many high-efficiency lamps they produce only a single output color, meaning that your eye won't be able to distinguish colors of objects illuminated solely by such a bulb. A lamp's ability for it to produce a natural variety of colors is measured by its CRI (Color Rendering Index).
But ultimately not more important than customers.