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why is the US not Metric

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IanB:

--- Quote from: Simon on October 27, 2019, 06:12:08 pm ---they are units of something per 1 of something else. It's metres per second, not metres per 10s. simens is the inverse of ohm, not the inverse of the measurement in ohms times 100

--- End quote ---

Simon, there may be engineering conventions in the world at large that you have not come across yet. For instance, it is common to express pressure drop in pipes as "psi per 100 ft" or "Pa per 100 m", and mechanical engineers find these to be perfectly good units of measurement.

Simon:
Pa per 100metres? wow, with what i deal in that would be a big number, no need to multiply it by 100. But these sound like things installers use as rules of thumb. Last pressure drop measurement i took was 80pa over 300mm that makes it in your units 26'600 Pa/100m. I'd preper to use 166Pa/m thankyou

james_s:

--- Quote from: IanB on October 27, 2019, 06:13:22 pm ---I remember being highly amused in 1970's Britain when I discovered a 12 V 60 W bulb with an ES base (for use in a car inspection lamp). At the time all domestic 240 V light fittings used a bayonet cap bulb and so it was impossible to mix things up. There were 240 V bulbs made with an ES or GES base, but these were mainly used in industrial or commercial settings, rarely in homes.

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At that time fluorescent tubes with ordinary BC caps on the ends were widely available there though, as were mercury vapor and SOX (low pressure sodium) lamps, any of which would be destroyed similarly by plugging one into an ordinary incandescent socket wired to 240V. They did use a 3 peg BC cap on HID lamps for a while but they were never common, I have a couple of the lamps but have never had a proper socket for one.

Today AC adapters with 2.1 and 2.5mm barrel plugs are widely used all over the world with all manner of different voltage ratings and no firm standard on polarity. I've seen a lot of stuff damaged by people assuming that if the plug fits it will work. You can't idiot-proof everything, sometimes one just has to use their brain a bit in order to navigate the world.

Zero999:

--- Quote from: vad on October 26, 2019, 10:57:11 pm ---
--- Quote from: wraper on October 26, 2019, 10:38:42 pm ---
--- Quote from: vad on October 26, 2019, 10:33:04 pm ---I, personally, have three problems with this particular device: (1) it is not UL-listed, (2) my nearest Home Depot does not stock 12VAC operated A19 LEDs, (3) I doubt it will work properly with Lurton Caseta dimmers.

--- End quote ---
No shit Sherlock. It's rated  for 230V AC therefore not for US market. And it's not a LED driver.

--- End quote ---
Thanks for letting me know before I ordered 50 of those. I was already pulling out credit card from the wallet.

--- End quote ---
That's what's commonly known as am electronic transformer. It's a Royer converter which outputs around 50kHz to 100kHz, modulated with double the mains frequency. There's no voltage regulation or rectification because it's designed for powering 12V halogen lamps and nothing else.

See the application note linked below.
https://www.st.com/content/ccc/resource/technical/document/application_note/e5/88/46/11/35/8c/4a/bf/CD00003902.pdf/files/CD00003902.pdf/jcr:content/translations/en.CD00003902.pdf



The only advantage I can think of for DC home wiring is, it would enable a large power factor corrected power supply to power many devices, rather than each using its own switched mode power supply, which will not have power factor correction. Of course this wouldn't mean distributing DC power over the grid, but converting it to something like 48V in every house. In reality it's not worth it because it would make wiring more difficult and most devices won't run directly off 48V, so more voltage conversion will still be required.

james_s:
There's a good reason for having higher voltage distributed everywhere anyway. There are lots of large loads, toasters, vacuum cleaners, space heaters, air conditioners, hair dryers, dehumidifiers, microwave ovens, coffee makers, etc. Sure I don't need these things in every room of the house but at one point or another I have used at least one of these high powered appliances in every room of my house and even 120V is marginal for many of them.

Power factor is not even really an issue for residential customers. Ideally we want it to be close to unity but it doesn't affect your bill in most places. If it were really a problem then a sensible way of sorting it out would be a central active PF correction device wired into the panel.

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