5 ms·

HVDC does have advantages in certain scenarios (very long transmission lines, for example) but parent is still correct--the majority of the grid makes way more

HVDC does have advantages in certain scenarios (very long transmission lines, for example) but parent is still correct--the majority of the grid makes way more sense with AC.

taeric 10y ago
I meant my follow-on to be a concession, but worded it poorly. I thought it had advantages, but yes, I was thinking small appliance mainly. In particular, in home. And not just computers, but lights and control panels. Seems many things all use the same power characteristics and are now becoming complicated by dealing with AC. Which, amusingly, is fitting for the tech debt debate. Eradicating some choices from the project is likely to be missing the point. Just as eradicating AC from all power would be short sighted/wrong.
- bluGill 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. It is much cheaper to have a power supply on every electronic device turning 100-200 volts to 5 volts than to have one big power supply turning power line voltage to 5 volts. Of course a lot of computers need 3 volts or less, so the power supplies exist anyway. It is also more efficient big power supplies running at low loads are inefficient, the power supply on each device is sized to what the device needs and so it more likely to be operating in a high efficiency area.
  - taeric 10y ago
    Including light bulbs?
    - CydeWeys 10y ago
      Yes, even light bulbs. A typical household LED is very easy to run off AC. You just need a capacitor big enough to hold the charge between each cycle of AC (which is very little). More information here: http://www.ledsmagazine.com/articles/2006/05/running-leds-from-an-ac-supply.html http://www.ledsmagazine.com/articles/2006/05/running-leds-fr... It'd be vastly more expensive to wire up an entire house for low voltage DC than it is to include the simple rectification components in every light bulb. In a house you're talking about many wire runs of many dozens of meters. This is not a good environment for low voltage DC at all.
      - taeric 10y ago
        I recall seeing IEEE articles talking about the DC wired home. I confess I stopped paying attention, as it will be a long time before this is actionable for me. Can't claim surprise to know that I had things that were wrong. Of course, the cynic (and, ironically optimist) in me still has this as evidence that "technical debt" is often used in BS circumstances by people that just don't fully understand the reasons for the things they are talking about. :)
  - 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.

HVDC does have advantages in certain scenarios (very long transmission lines, for example) but parent is still correct--the majority of the grid makes way more sense with AC.

taeric 10y ago

I meant my follow-on to be a concession, but worded it poorly. I thought it had advantages, but yes, I was thinking small appliance mainly. In particular, in home. And not just computers, but lights and control panels. Seems many things all use the same power characteristics and are now becoming complicated by dealing with AC. Which, amusingly, is fitting for the tech debt debate. Eradicating some choices from the project is likely to be missing the point. Just as eradicating AC from all power would be short sighted/wrong.

bluGill 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. It is much cheaper to have a power supply on every electronic device turning 100-200 volts to 5 volts than to have one big power supply turning power line voltage to 5 volts. Of course a lot of computers need 3 volts or less, so the power supplies exist anyway. It is also more efficient big power supplies running at low loads are inefficient, the power supply on each device is sized to what the device needs and so it more likely to be operating in a high efficiency area.
- taeric 10y ago
  Including light bulbs?
  - CydeWeys 10y ago
    Yes, even light bulbs. A typical household LED is very easy to run off AC. You just need a capacitor big enough to hold the charge between each cycle of AC (which is very little). More information here: http://www.ledsmagazine.com/articles/2006/05/running-leds-from-an-ac-supply.html http://www.ledsmagazine.com/articles/2006/05/running-leds-fr... It'd be vastly more expensive to wire up an entire house for low voltage DC than it is to include the simple rectification components in every light bulb. In a house you're talking about many wire runs of many dozens of meters. This is not a good environment for low voltage DC at all.
    - taeric 10y ago
      I recall seeing IEEE articles talking about the DC wired home. I confess I stopped paying attention, as it will be a long time before this is actionable for me. Can't claim surprise to know that I had things that were wrong. Of course, the cynic (and, ironically optimist) in me still has this as evidence that "technical debt" is often used in BS circumstances by people that just don't fully understand the reasons for the things they are talking about. :)
- 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.