6 ms·

I've been wondering more than once if we couldn't improve (larger) offices a lot by distributing power pre-transformed so every computer and every screen wouldn

I've been wondering more than once if we couldn't improve (larger) offices a lot by distributing power pre-transformed so every computer and every screen wouldn't have to include a transformer. I also sometimes wonder why these days, when every new lamp is led, why we don't replace most of the dangerous 230V outlets in new houses with 12V and use 230V only for dishwashers, laundry machines, dryers and that kind of stuff. Is there some kind engineer or hobbyist here who could shoot this idea down for me so it won't bother me for another 3 years? (I have a couple of years studies in electronics, but not power distribution. I think I understand why backbone networks uses extremely high voltages to reduce losses, but at least for now think it is more a issue over long distances, but I am willing to reconsider.)

abakker 3y ago
Transmission losses in DC are higher, so you need a lot more wire. You actually can get off the shelf low voltage lighting, though, but it tends to be high end designer stuff.
- cesarb 3y ago
  > Transmission losses in DC are higher For the same voltage and wire size, transmission losses in DC are the same or lower (due to skin effect and capacitive/inductive losses). They are only higher when comparing low-voltage DC with higher-voltage AC, but the key difference is the voltage, not DC versus AC. (As a bonus, DC has lower peak voltage for the same RMS voltage, so the wires need less insulation.)
  - appletrotter 3y ago
    Sure, but GP and OP are talking about supplying power at the voltages devices (such as LEDs) currently consume. AC is associated with higher voltage in this context even if that isn’t intrinsic.
- IshKebab 3y ago
  Nah 12V MR16 lights are quite common.
sbierwagen 3y ago
Many IP phones are PoE. Ubiquiti used to sell PoE office lighting, oddly enough. Now discontinued https://www.bhphotovideo.com/c/product/1431160-REG/ubiquiti_networks_uled_at_2_unifi_led_panel.html https://www.bhphotovideo.com/c/product/1431160-REG/ubiquiti_...
- smileybarry 3y ago
  It's kind of cool that you'd control lighting over IP supplied via the same PoE port, but a missed opportunity to not offer a unit with an AP inside.
  - sbierwagen 3y ago
    It really is bonkers. I wonder if it was the case of a VP with a pet project who pushed it hard to ship, got a promotion to a different org, at which point it was promptly canceled. Only makes sense if it had a line of sight wireless AP in it, like 40 ghz or (to a lesser extent) the new 6 ghz band.
hunter2_ 3y ago
For a given wattage, voltage and current can be adjusted (inversely proportional) within reason, but higher current with lower voltage results in some problems: voltage drop (which mostly only matters at long distances, typically negligible within an office) and thicker conductors (double the cross-sectional area for double the current, if memory serves). This is why things like PoE and phantom power for audio are often 48V instead of something lower.
crote 3y ago
Office equipment doesn't really have "transformers" anymore, everything uses switched-mode power supplies. The way they work, is that they have an output buffer (a capacitor or inductor) and rapidly turn a switch on and off to keep that output buffer at the right level: if the output buffer is below the target voltage, the switch closes and the voltage will start to rise. Once the output buffer rises above the target voltage, the switch opens and the voltage will drop as power is being used from the buffer. This happens thousands or even millions of times per second. This principle works exactly the same for modern AC/DC power supplies as it does for DC/DC ones. The problem with your plan is Ohm's Law, and more specifically that fact that wires aren't perfect and have some resistance (for now!). Ohm's Law gives us V=I*R, where V is the voltage in volts (V), I is the current in ampere (A), and R is the resistance in Ohm (Ω). In a wire, the resistance is constant, and V is the voltage loss across the wire. So how do we reduce the loss? We reduce I. Luckily we only actually care about the total power, which is given by P=U*I. If we want the power to stay the same and reduce the current, we have to increase the voltage. Let's say the two wires from our central transformer to the computer are 14-gage copper, and they are 100 feet long. Their resistance is about 0.5Ω combined. We want to power a 120W computer. If we transfer that at 12V (the normal voltage computers use internally), we'd have to transfer 120W/12V=10A. The voltage loss across our wires is 10A*0.5Ω = 5V! So we put in 12V, but get out only 7V as we burned 50W in the cable itself. To get out the desired 12V we'd have to put in 17V at 10A instead, or 170W to power a 120W computer. It would also mean supplying way too high of a voltage to a computer connected with a 3-foot cable. If we increase the voltage across the wires to 120V and down-convert that to 12V at the computer we'd only need to conduct 1A and the wire loss would be 0.5V, which at 1A is a power loss of 0.5W. That's completely acceptable, and because the computer down-converts anyways we don't really have to care about it getting 119.5V instead of 120V either. But now we are back with a power supply at each individual computer, so in the end we didn't really gain anything. Instead of an AC/DC power supply in every computer we now have a virtually identical DC/DC power supply, so what's the point? You might have some small gains by doing the initial AC/DC conversion centrally, but in practice it probably isn't enough to care. It is only really worth it when your power comes from DC anyways, like an office with rooftop solar. Alternatively we can use way thicker cables, but to get that same 0.5W loss at 10A would mean a wire with a resistance of 0.005Ω. To illustrate, that means using two 0000 AWG wires in parallel.
forgotusername6 3y ago
Plenty of domestic applications still require higher voltage (well actually power but I presume you aren't suggesting 12V with high current). Vacuum cleaners, hair dryers, anything portable that produces heat. Building houses with low voltage sockets would be really frustrating for people living there. Is the danger of 230V actually significant in this day and age? I wonder how many fires/injuries are caused by 230V that wouldn't happen at a low voltage.
- Cthulhu_ 3y ago
  Fires and injuries at 230V aren't caused by the voltage, but by improper installation and handling. Don't stick forks in outlets, turn the power off when you're working with it, etc. Also, it's not the voltage that kills you, it's the amperage. With regards to the 12V discussion, there's also AC vs DC to consider; AC will flip voltage 60x a second, making your heart go haywire, whereas DC is a continuous jolt, meaning your heart and other muscles will freeze in place until the power is released again, like how a defibrillator works.
  - SkeuomorphicBee 3y ago
    > Also, it's not the voltage that kills you, it's the amperage. A bit off-topic but I never liked that saying, it is kind-of-right but also soo wrong in so many levels. Amperage is not a thing that happens on its own, it is always a result of voltage, voltage is the driving force, so it is the voltage that actively kills you, by forcing amperage through your internals. When the killing happens the voltage is the real murderer, the amperage is just the murder weapon.
    - tnecniv 3y ago
      My hypothesis has been that the saying is due to how we generally think about power supplies. The voltage is a fixed quantity but the current fluctuates based on what the circuit asks for and what the power supply can give you. Something could be rated at 100V, but if the supply can’t deliver any significant amps it doesn’t matter much
  - 3y ago
Cthulhu_ 3y ago
At best I've seen USB ports in wall and desk outlets, but I suspect they have transformers inside the housing.
awiesenhofer 3y ago
I have this vision of a future where everything just runs off of usb-c and usb-pd. Even today, expect in the kitchen and the bathroom (refrigerator, washing machine,...) you could totally run most things off of the 240w max. Much more so in an office. It would be so much more efficient than what we have now, and safer. No idea how realistic it is though...
- t3rabytes 3y ago
  I pulled the specs for a dual-compressor fridge this morning for an unrelated reason and it only draws 180w... maybe the fridge can run on usb-c too! https://www.bosch-home.com/us/productslist/refrigerators/fridge-freezers/freestanding-fridge-freezers-with-freezer-at-bottom/B36CT81ENS#/Tabs=section-technicalspecs/Togglebox=accessories/Togglebox=accessoriesOthers/Togglebox=manuals/ https://www.bosch-home.com/us/productslist/refrigerators/fri...
  - smileybarry 3y ago
    Something about a giant fridge being powered by some small Apple brick gives me shivers. I guess it's doable but it feels wrong.

abakker 3y ago

Transmission losses in DC are higher, so you need a lot more wire. You actually can get off the shelf low voltage lighting, though, but it tends to be high end designer stuff.

cesarb 3y ago
> Transmission losses in DC are higher For the same voltage and wire size, transmission losses in DC are the same or lower (due to skin effect and capacitive/inductive losses). They are only higher when comparing low-voltage DC with higher-voltage AC, but the key difference is the voltage, not DC versus AC. (As a bonus, DC has lower peak voltage for the same RMS voltage, so the wires need less insulation.)
- appletrotter 3y ago
  Sure, but GP and OP are talking about supplying power at the voltages devices (such as LEDs) currently consume. AC is associated with higher voltage in this context even if that isn’t intrinsic.
IshKebab 3y ago
Nah 12V MR16 lights are quite common.

sbierwagen 3y ago

Many IP phones are PoE. Ubiquiti used to sell PoE office lighting, oddly enough. Now discontinued https://www.bhphotovideo.com/c/product/1431160-REG/ubiquiti_networks_uled_at_2_unifi_led_panel.html https://www.bhphotovideo.com/c/product/1431160-REG/ubiquiti_...

smileybarry 3y ago
It's kind of cool that you'd control lighting over IP supplied via the same PoE port, but a missed opportunity to not offer a unit with an AP inside.
- sbierwagen 3y ago
  It really is bonkers. I wonder if it was the case of a VP with a pet project who pushed it hard to ship, got a promotion to a different org, at which point it was promptly canceled. Only makes sense if it had a line of sight wireless AP in it, like 40 ghz or (to a lesser extent) the new 6 ghz band.

hunter2_ 3y ago

For a given wattage, voltage and current can be adjusted (inversely proportional) within reason, but higher current with lower voltage results in some problems: voltage drop (which mostly only matters at long distances, typically negligible within an office) and thicker conductors (double the cross-sectional area for double the current, if memory serves). This is why things like PoE and phantom power for audio are often 48V instead of something lower.

crote 3y ago

Office equipment doesn't really have "transformers" anymore, everything uses switched-mode power supplies. The way they work, is that they have an output buffer (a capacitor or inductor) and rapidly turn a switch on and off to keep that output buffer at the right level: if the output buffer is below the target voltage, the switch closes and the voltage will start to rise. Once the output buffer rises above the target voltage, the switch opens and the voltage will drop as power is being used from the buffer. This happens thousands or even millions of times per second. This principle works exactly the same for modern AC/DC power supplies as it does for DC/DC ones. The problem with your plan is Ohm's Law, and more specifically that fact that wires aren't perfect and have some resistance (for now!). Ohm's Law gives us V=I*R, where V is the voltage in volts (V), I is the current in ampere (A), and R is the resistance in Ohm (Ω). In a wire, the resistance is constant, and V is the voltage loss across the wire. So how do we reduce the loss? We reduce I. Luckily we only actually care about the total power, which is given by P=U*I. If we want the power to stay the same and reduce the current, we have to increase the voltage. Let's say the two wires from our central transformer to the computer are 14-gage copper, and they are 100 feet long. Their resistance is about 0.5Ω combined. We want to power a 120W computer. If we transfer that at 12V (the normal voltage computers use internally), we'd have to transfer 120W/12V=10A. The voltage loss across our wires is 10A*0.5Ω = 5V! So we put in 12V, but get out only 7V as we burned 50W in the cable itself. To get out the desired 12V we'd have to put in 17V at 10A instead, or 170W to power a 120W computer. It would also mean supplying way too high of a voltage to a computer connected with a 3-foot cable. If we increase the voltage across the wires to 120V and down-convert that to 12V at the computer we'd only need to conduct 1A and the wire loss would be 0.5V, which at 1A is a power loss of 0.5W. That's completely acceptable, and because the computer down-converts anyways we don't really have to care about it getting 119.5V instead of 120V either. But now we are back with a power supply at each individual computer, so in the end we didn't really gain anything. Instead of an AC/DC power supply in every computer we now have a virtually identical DC/DC power supply, so what's the point? You might have some small gains by doing the initial AC/DC conversion centrally, but in practice it probably isn't enough to care. It is only really worth it when your power comes from DC anyways, like an office with rooftop solar. Alternatively we can use way thicker cables, but to get that same 0.5W loss at 10A would mean a wire with a resistance of 0.005Ω. To illustrate, that means using two 0000 AWG wires in parallel.

forgotusername6 3y ago

Plenty of domestic applications still require higher voltage (well actually power but I presume you aren't suggesting 12V with high current). Vacuum cleaners, hair dryers, anything portable that produces heat. Building houses with low voltage sockets would be really frustrating for people living there. Is the danger of 230V actually significant in this day and age? I wonder how many fires/injuries are caused by 230V that wouldn't happen at a low voltage.

Cthulhu_ 3y ago
Fires and injuries at 230V aren't caused by the voltage, but by improper installation and handling. Don't stick forks in outlets, turn the power off when you're working with it, etc. Also, it's not the voltage that kills you, it's the amperage. With regards to the 12V discussion, there's also AC vs DC to consider; AC will flip voltage 60x a second, making your heart go haywire, whereas DC is a continuous jolt, meaning your heart and other muscles will freeze in place until the power is released again, like how a defibrillator works.
- SkeuomorphicBee 3y ago
  > Also, it's not the voltage that kills you, it's the amperage. A bit off-topic but I never liked that saying, it is kind-of-right but also soo wrong in so many levels. Amperage is not a thing that happens on its own, it is always a result of voltage, voltage is the driving force, so it is the voltage that actively kills you, by forcing amperage through your internals. When the killing happens the voltage is the real murderer, the amperage is just the murder weapon.
  - tnecniv 3y ago
    My hypothesis has been that the saying is due to how we generally think about power supplies. The voltage is a fixed quantity but the current fluctuates based on what the circuit asks for and what the power supply can give you. Something could be rated at 100V, but if the supply can’t deliver any significant amps it doesn’t matter much
- 3y ago

Cthulhu_ 3y ago

At best I've seen USB ports in wall and desk outlets, but I suspect they have transformers inside the housing.

awiesenhofer 3y ago

I have this vision of a future where everything just runs off of usb-c and usb-pd. Even today, expect in the kitchen and the bathroom (refrigerator, washing machine,...) you could totally run most things off of the 240w max. Much more so in an office. It would be so much more efficient than what we have now, and safer. No idea how realistic it is though...

t3rabytes 3y ago
I pulled the specs for a dual-compressor fridge this morning for an unrelated reason and it only draws 180w... maybe the fridge can run on usb-c too! https://www.bosch-home.com/us/productslist/refrigerators/fridge-freezers/freestanding-fridge-freezers-with-freezer-at-bottom/B36CT81ENS#/Tabs=section-technicalspecs/Togglebox=accessories/Togglebox=accessoriesOthers/Togglebox=manuals/ https://www.bosch-home.com/us/productslist/refrigerators/fri...
- smileybarry 3y ago
  Something about a giant fridge being powered by some small Apple brick gives me shivers. I guess it's doable but it feels wrong.