5 ms·

>AC is much better in the home. There is no way to get around the fact that you need massive wires to supply low voltage at high amps. That's orthogonal. What

by Arizhel 10y ago

>AC is much better in the home. There is no way to get around the fact that you need massive wires to supply low voltage at high amps. That's orthogonal. What you really mean is that you want high(ish) voltage to distribute power in a home, in order to mimimize losses due to wire resistance over distances of dozens of meters. You don't need AC to do that. In fact, with modern power electronics, the switching converters we now use for supplying LVDC to our devices can work just as well with DC as with AC input power. The primary advantage of AC over DC is that it can be converted between voltage levels easily with transformers. But today, we can do the same thing with DC using DC-to-DC converters. These didn't really exist in an economical way before a couple decades ago, maybe even more recently. If for some odd reason, western society decided to re-engineer and replace the whole power grid, it's quite likely I think they would simply switch to DC for everything. With deployment at that scale, the cost issues with the equipment should go away, making it no more expensive to replace everything with DC converters than transformers. DC is more efficient than AC because it stays at its peak voltage, and because it has no skin effect. But the technology needed to make it inexpensive to use for power transmission has only been around for a somewhat short time (namely, modern power electronics). Up until recently, it was simply a no-brainer to use AC because of its simplicity in generation, transmission (with transformers for stepping up the voltage), and usage (with AC motors).

taeric 10y ago
I'd be interested in you two debating this more, since you both clearly know the topic better than I do. This post is reflecting what I thought I had heard. But, I am not in this field.
- Arizhel 10y ago
  There's really nothing to debate; the guy I replied to was totally correct about everything except the bit about "AC is much better in the home", where I pointed out that he really meant that a high voltage roughly where our current AC systems are (120V-240V) is much better in the home than some kind of low-voltage DC system, and that with modern technology, it would probably actually be better to have a DC system. But realistically, that's not going to happen because the gains (probably very minimal) aren't worthwhile compared to the enormous cost of conversion, given how standardized our current AC system is and how all our infrastructure, point-of-use devices, etc. are all designed around that. Basically, he was assuming practical real-world considerations, I'm going off on a tangent about ideal conditions. His argument is about whether it's better to stick with the current AC system that your house has, or if it's better to install a low-voltage DC system to supply 5V, 12V, etc. to all your devices from a single, central, whole-house power supply as many people who don't understand electricity will frequently suggest. He's completely correct: low-voltage DC is a terrible way to supply power over any distance more than a meter or two because of resistive losses, so it'd require massively large copper cables or busbars. And power supplies are generally very low-efficiency when operated at low load. So our current approach (separate little optimized power supplies for every device, plugged into a higher-voltage AC supply) is actually optimal.
  - taeric 10y ago
    I was never arguing that an individual should replace the AC in their house. My argument was, with current technology, the AC setup can be seen as tech debt. Which seems compatible with what you are saying, but the parent was specifically claiming I was wrong. That is, you seem to be echoing my point. But seem to be claiming it is different. What am I missing?
    - Arizhel 10y ago
      I wouldn't call it "tech debt". Present-day AC systems may not be completely optimal (given current electronics technology), but they do work well. As I understand it, "tech debt" is something that has to be reckoned with at some point, or else you're going to have real problems in the future (just like refusing to pay off a money debt will generally cause you real problems at some point when the creditor sues you and gets a judgment). You can't just let it go on forever; eventually you need to "pay it down" (by cleaning up the codebase, migrating to newer technologies, etc.), or else catastrophe happens (the company is unable to compete and goes under). One common factor cited in these stories is that the code becomes too unmaintainable and unreliable: too many weird changes for customers pile up and introduce serious bugs which cause the product to not work properly. This isn't like that at all. We can go on with our current household AC power systems indefinitely. Maybe we could get a 1% improvement by switching to DC systems (at an enormous cost because most of your appliances and devices won't work with it without adapters), I don't really know exactly how much better DC would be (not much really), but what we have now works fine. Furthermore, it's not like the whole electric grid system needs to be changed: it's entirely possible, for instance, to switch distribution systems to DC and leave household systems AC. Instead of distributing the power at 30-something kVAC in your neighborhood and using outdoor transformers to step it down to 240VAC for your house, it could be distributed in DC form, and those transformers replaced by modules which convert the 30-something kVDC to 240VAC. In the old days, this was hard and expensive to do, but with modern power electronics it's not. But even here, the question is: are the gains worth the expense? And the answer is very likely "no". (For reference, I'm not a power engineer, I just studied it in college as a small part of my EE curriculum.) So this does not, to me, resemble "tech debt" at all. It's just a system that we use for legacy reasons and which is extremely reliable and works well, even though it might not be the absolute most efficient way to solve the problem. This is no different than many other engineered systems. Perhaps you have a decent and extremely reliable car. Could it be better? Sure: you could build the chassis out of carbon fiber, use forged aluminum wheels instead of cast, etc. all to save weight and improve fuel economy. Are you going to do that? Of course not, because the cost is astronomical. There's cars like that now, and they cost $1M+. So for AC systems that we're talking about, the question is: what is wrong with them that we want to consider replacing them with something else, instead of just sticking with them even if they're not quite as efficient as they could be? Because the cost to upgrade them would be enormous, so you need to have a very good reason.
bluGill 10y ago
> it's quite likely I think they would simply switch to DC for everything I'm not sure. AC has some important safety considerations that would make it better even if the efficient was significantly worse. Switches, fuses and circuit breakers that work with DC are more expensive than AC. When a circuit opens there is a spark, and this spark can in some cases create a conductive plasma. With AC the wave goes to zero and the plasma disappears, while with DC it continues. There are cases where a DC fuse blew but the fuse continued to conduct. Of course this can be engineered around, but generally with larger and more expensive parts. When someone touches power accidentally, AC is slightly safer. With DC your muscles will grab and never let go. AC gives you a chance to let go. This is a low probability thing, but is a factor. The guy who wanted us to debate is wrong for one other reason though: I'm approaching the limits of what I know on the subject, while you seem to have a lot more knowledge.
- taeric 10y ago
  The desire for debate was to increase our collective knowledge. Not to prove someone right. I am fully comfortable with the idea that I was wrong. You both have knowledge I find interesting.

by Arizhel 10y ago

taeric 10y ago

I'd be interested in you two debating this more, since you both clearly know the topic better than I do. This post is reflecting what I thought I had heard. But, I am not in this field.

Arizhel 10y ago
There's really nothing to debate; the guy I replied to was totally correct about everything except the bit about "AC is much better in the home", where I pointed out that he really meant that a high voltage roughly where our current AC systems are (120V-240V) is much better in the home than some kind of low-voltage DC system, and that with modern technology, it would probably actually be better to have a DC system. But realistically, that's not going to happen because the gains (probably very minimal) aren't worthwhile compared to the enormous cost of conversion, given how standardized our current AC system is and how all our infrastructure, point-of-use devices, etc. are all designed around that. Basically, he was assuming practical real-world considerations, I'm going off on a tangent about ideal conditions. His argument is about whether it's better to stick with the current AC system that your house has, or if it's better to install a low-voltage DC system to supply 5V, 12V, etc. to all your devices from a single, central, whole-house power supply as many people who don't understand electricity will frequently suggest. He's completely correct: low-voltage DC is a terrible way to supply power over any distance more than a meter or two because of resistive losses, so it'd require massively large copper cables or busbars. And power supplies are generally very low-efficiency when operated at low load. So our current approach (separate little optimized power supplies for every device, plugged into a higher-voltage AC supply) is actually optimal.
- taeric 10y ago
  I was never arguing that an individual should replace the AC in their house. My argument was, with current technology, the AC setup can be seen as tech debt. Which seems compatible with what you are saying, but the parent was specifically claiming I was wrong. That is, you seem to be echoing my point. But seem to be claiming it is different. What am I missing?
  - Arizhel 10y ago
    I wouldn't call it "tech debt". Present-day AC systems may not be completely optimal (given current electronics technology), but they do work well. As I understand it, "tech debt" is something that has to be reckoned with at some point, or else you're going to have real problems in the future (just like refusing to pay off a money debt will generally cause you real problems at some point when the creditor sues you and gets a judgment). You can't just let it go on forever; eventually you need to "pay it down" (by cleaning up the codebase, migrating to newer technologies, etc.), or else catastrophe happens (the company is unable to compete and goes under). One common factor cited in these stories is that the code becomes too unmaintainable and unreliable: too many weird changes for customers pile up and introduce serious bugs which cause the product to not work properly. This isn't like that at all. We can go on with our current household AC power systems indefinitely. Maybe we could get a 1% improvement by switching to DC systems (at an enormous cost because most of your appliances and devices won't work with it without adapters), I don't really know exactly how much better DC would be (not much really), but what we have now works fine. Furthermore, it's not like the whole electric grid system needs to be changed: it's entirely possible, for instance, to switch distribution systems to DC and leave household systems AC. Instead of distributing the power at 30-something kVAC in your neighborhood and using outdoor transformers to step it down to 240VAC for your house, it could be distributed in DC form, and those transformers replaced by modules which convert the 30-something kVDC to 240VAC. In the old days, this was hard and expensive to do, but with modern power electronics it's not. But even here, the question is: are the gains worth the expense? And the answer is very likely "no". (For reference, I'm not a power engineer, I just studied it in college as a small part of my EE curriculum.) So this does not, to me, resemble "tech debt" at all. It's just a system that we use for legacy reasons and which is extremely reliable and works well, even though it might not be the absolute most efficient way to solve the problem. This is no different than many other engineered systems. Perhaps you have a decent and extremely reliable car. Could it be better? Sure: you could build the chassis out of carbon fiber, use forged aluminum wheels instead of cast, etc. all to save weight and improve fuel economy. Are you going to do that? Of course not, because the cost is astronomical. There's cars like that now, and they cost $1M+. So for AC systems that we're talking about, the question is: what is wrong with them that we want to consider replacing them with something else, instead of just sticking with them even if they're not quite as efficient as they could be? Because the cost to upgrade them would be enormous, so you need to have a very good reason.

bluGill 10y ago

> it's quite likely I think they would simply switch to DC for everything I'm not sure. AC has some important safety considerations that would make it better even if the efficient was significantly worse. Switches, fuses and circuit breakers that work with DC are more expensive than AC. When a circuit opens there is a spark, and this spark can in some cases create a conductive plasma. With AC the wave goes to zero and the plasma disappears, while with DC it continues. There are cases where a DC fuse blew but the fuse continued to conduct. Of course this can be engineered around, but generally with larger and more expensive parts. When someone touches power accidentally, AC is slightly safer. With DC your muscles will grab and never let go. AC gives you a chance to let go. This is a low probability thing, but is a factor. The guy who wanted us to debate is wrong for one other reason though: I'm approaching the limits of what I know on the subject, while you seem to have a lot more knowledge.

taeric 10y ago
The desire for debate was to increase our collective knowledge. Not to prove someone right. I am fully comfortable with the idea that I was wrong. You both have knowledge I find interesting.