General > General Technical Chat

why is the US not Metric

<< < (11/291) > >>

tooki:

--- Quote from: vad on October 25, 2019, 07:42:56 pm ---
--- Quote from: richard.cs on October 25, 2019, 02:51:02 pm ---You might as well ask when North America will join the 230 V world :-D Lots of advantages there (~3 kW available for common domestic appliances, lower final circuit currents leading to fewer fires and higher energy efficiency, eventual death of split-phase and weird stuff like high leg delta).
--- End quote ---
I would rather see the world adopting low-voltage DC residential electric circuits for lighting and electronics. At home I have about a hundred devices ranging from LED lamps to phone charges that don’t really need 120V, each with its own mains-operated LED driver or isolated SMPS (what a waste!), and only a handful appliances that genuinely benefit from 120VAC and two-phase 240VAC supply.

--- End quote ---
Though I understand the thinking behind that, that that would simply shift the waste elsewhere in the system. Suppose we used the 5V standard from regular USB. A desktop computer might need 300W, which is 60A at 5V. That's some seriously thick wiring.

A standard US residential circuit can provide 1800W (120Vx15A). At 5V, that's 360A, which would require insanely thick wire in the walls (over 100x as thick as what we can use at 120V, according to the national electrical code). Even if we used 24V, that'd still be 75A, still needing wire many times thicker than what we use now. With copper prices higher than ever, that makes absolutely no sense.

And the connectors needed for that would be crazy, as would the circuit breakers and switches, all of which would need to be able to handle massive arcing.

Rather than reducing the voltage of the power in the house, what we need to do is to raise the voltage of the devices themselves. This is precisely what USB Power Delivery does, allowing devices to request up to 20V, so that they can carry far greater power over thinner cable.

vad:

--- Quote from: Monkeh on October 25, 2019, 07:50:00 pm ---
--- Quote from: vad on October 25, 2019, 07:42:56 pm ---
--- Quote from: richard.cs on October 25, 2019, 02:51:02 pm ---You might as well ask when North America will join the 230 V world :-D Lots of advantages there (~3 kW available for common domestic appliances, lower final circuit currents leading to fewer fires and higher energy efficiency, eventual death of split-phase and weird stuff like high leg delta).
--- End quote ---
I would rather see the world adopting low-voltage DC residential electric circuits for lighting and electronics. At home I have about a hundred devices ranging from LED lamps to phone charges that don’t really need 120V, each with its own mains-operated LED driver or isolated SMPS (what a waste!), and only a handful appliances that genuinely benefit from 120VAC and two-phase 240VAC supply.

--- End quote ---

So instead you want the greater expense and complexity of switching and protecting DC circuits and, translating to actual standards, the losses involved in ELV distribution.

Yes, this makes much sense.

--- End quote ---
Hell yes, if that would prevent LED lights from flickering and LED driver popping because of overheating. Switching and protecting 12VDC / 15A branch circuit is not that much expensive than switching and protecting 120VAC / 15A circuit.

vad:

--- Quote from: tooki on October 25, 2019, 08:08:28 pm ---
--- Quote from: vad on October 25, 2019, 07:42:56 pm ---
--- Quote from: richard.cs on October 25, 2019, 02:51:02 pm ---You might as well ask when North America will join the 230 V world :-D Lots of advantages there (~3 kW available for common domestic appliances, lower final circuit currents leading to fewer fires and higher energy efficiency, eventual death of split-phase and weird stuff like high leg delta).
--- End quote ---
I would rather see the world adopting low-voltage DC residential electric circuits for lighting and electronics. At home I have about a hundred devices ranging from LED lamps to phone charges that don’t really need 120V, each with its own mains-operated LED driver or isolated SMPS (what a waste!), and only a handful appliances that genuinely benefit from 120VAC and two-phase 240VAC supply.

--- End quote ---
Though I understand the thinking behind that, that that would simply shift the waste elsewhere in the system. Suppose we used the 5V standard from regular USB. A desktop computer might need 300W, which is 60A at 5V. That's some seriously thick wiring.

A standard US residential circuit can provide 1800W (120Vx15A). At 5V, that's 360A, which would require insanely thick wire in the walls (over 100x as thick as what we can use at 120V, according to the national electrical code). Even if we used 24V, that'd still be 75A, still needing wire many times thicker than what we use now. With copper prices higher than ever, that makes absolutely no sense.

And the connectors needed for that would be crazy, as would the circuit breakers and switches, all of which would need to be able to handle massive arcing.

Rather than reducing the voltage of the power in the house, what we need to do is to raise the voltage of the devices themselves. This is precisely what USB Power Delivery does, allowing devices to request up to 20V, so that they can carry far greater power over thinner cable.

--- End quote ---
My point is - majority of the devices in a typical modern home are low-power low-voltage devices. Having, let say 12VDC / 10A branches in my home, in addition to existing 120VAC and two-phase 240 VAC circuits makes a lot of sense for powering such devices.

Zero999:

--- Quote from: xmetal on October 25, 2019, 03:58:15 pm ---I tend to use Fahrenheit for higher weather temperatures and Celsius for the lower ones.

--- End quote ---

--- Quote from: NivagSwerdna on October 25, 2019, 10:47:03 am ---In the UK we still have road distances and speed limits in miles despite having most other things in SI units... strange really.
... and when it is really hot the tabloid papers say... "Oooo what a scorcher <big number>F"... I seriously doubt many people understand F in the UK now... not me anyway.  :)

--- End quote ---
That's true, especially with higher temperatures. The BBC gave the temperature in both Fahrenheit and Celsius, when the heatwave in the summer just gone, broke the UK temperature, by reaching  38.7°C (101.7°F), yet the record breaking temperature in winter, at 21.2°C was only given in Celsius.
https://www.bbc.co.uk/news/uk-49157898
https://www.bbc.co.uk/news/uk-47374936

I wonder if it's because 101.7°F sounds more impressive than 70.2°F?

I think we should all use Kelvin for temperature. Celsius is no better than Fahrenheit because both scales have negative numbers which are totally unnecessary.

tooki:

--- Quote from: vad on October 25, 2019, 08:18:50 pm ---My point is - majority of the devices in a typical modern home are low-power low-voltage devices. Having, let say 12VDC / 10A branches in my home, in addition to existing 120VAC and two-phase 240 VAC circuits makes a lot of sense for powering such devices.

--- End quote ---
I understand the appeal, but a 12V/10A circuit is just 120W, and you would easily bog that down with just a few lights and things. (For context, a mere 3 foot segment of LED tape is 1A.) I think people don't realize how much current many of their low-voltage devices draw! A cellphone charging is around 12W (which can be 2.4A at 5V, or sometimes less current at higher voltage), another amp at 12V. Little LED desk or night table lamp? Another half an amp. Next thing you know, your "low power" circuits are overloaded.

What does make some sense is to have low-voltage AC->DC power supplies that can handle multiple devices. I've been doing this, by replacing power strips full of individual USB chargers with 6- and 10-port chargers.

P.S. US 120/240V circuits aren't two-phase, it's a split-phase system. The 120V circuits are created from a single 240V phase, by using a center-tapped transformer.

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod