General > General Technical Chat
why is the US not Metric
Monkeh:
--- Quote from: vad on October 26, 2019, 02:47:59 pm ---I totally agree. The example of 12VDC / 10A that I gave was a marginal case, just to show feasibility even at such low voltage. Higher DC voltages (24...48V) can deliver greater power and would be less expensive both in installations and material costs. 12-14AWG that is commonly used for residential wiring is 2-3 times less expensive than 10AWG needed for 12V / 120W, and is easier to work with.
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Would you make up your mind?
He suggested point of load converters. Which we already have, and you already rejected.
12V, 150W, and no need for running 10AWG around the place. Already exists, already used, we have USB capable of 100W for devices.
Simon:
--- Quote from: syau on October 26, 2019, 12:04:31 pm ---
The worst thing is the wire gauge size AWG vs mm, due to slightly different in diameter, 2 set of wire stripper is required |O
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Yea, I hate that but have to work with it.
bdunham7:
--- Quote from: blueskull on October 26, 2019, 12:20:54 am ---
--- Quote from: Monkeh on October 26, 2019, 12:16:00 am ---
--- Quote ---240V is a two-phase system with a neutral wire and two hot wires running at 180 degrees phase shift.
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No.. it's definitely single-phase centre-tapped.
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What makes "phases" must be 120 degrees apart from each other?
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They don't have to be 120 degrees--the original polyphase , aka 'two-phase' had phases 90 degrees apart. And you don't necessarily have to evenly space them, I suppose...
However, the real point of understanding is knowing when equivalence by superimposition occurs. We all understand that compass readings of 0 and 360 degrees are equivalent, but in power phases, this equivalence occurs at 180 degrees. In other words, simply reversing the polarity of a phase doesn't give you another phase.
james_s:
--- Quote from: vad on October 26, 2019, 03:41:51 am ---Add a tumble drier, air conditioner, a fridge, a washing machine, a gaming desktop computer and a hair dryer. That makes it 9 appliances that need 120V or 240V. Almost everything else can be powered from low-voltage low-power supply. I have many dozens of LED A19 lamps alone
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Do you have any idea what you're talking about? Have you looked into the cost of 10AWG wire or calculated the losses you'd end up with? There's a good reason that aircraft and large trucks have historically been 28V and there is talk to changing cars to 48V. What do you think 12V would solve for lighting? Are LEDs going to magically run cooler if the driver is fed by 12V instead of 120V? My house is almost entirely LED since I changed it out in 2011-2013 and I think I have had 3 bulbs fail in that time, all of which were in enclosed fixtures, I have since found some bulbs that don't seem to mind that. Nobody in their right mind with any understanding of EE would contemplate wiring a house for 12V. Try living in an RV or boat for a while and you'll quickly realize what a hassle it is to be stuck with such a low voltage. A 2V sag under load is no problem for 120V but it's completely unacceptable for 12V.
If we were to contemplate changing anything it would be far more sensible to increase the household voltage to 240V rather than reduce it to something stupid. Incandescent lamps are for the most part obsolete so the major disadvantage of the efficiency penalty for higher voltage incandescent lamps is gone. Voltage conversion is cheap and efficient now so it can be done at the point of use when needed. Less copper, lower losses, lower cost, there are lots of advantages. But not really enough to change it at this point, 120V works fine.
rstofer:
--- Quote from: Simon on October 26, 2019, 07:44:46 am ---the C/K conversion is easy and for the average person and general convenience having 0 as water freezing is nice. Kelvin would still not solve everything with negative numbers or rather conversions. Auto standards do not go lower than -40C. In a CAN bus message where you only have 8 bits available for temperature and want to go as high as engine temperatures the 0 starts at -40C. In kelvin a similar translation would be required. No one will ever have to work with near 0K temperatures so it's a bit pointless using that as the starting point in every day life.
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Just so the US doesn't get stuck with C and Kelvin, we have Rankine as our absolute zero referenced temperature (like K) but scaled in Fahrenheit. Oddly, it wasn't discussed in my grandson's Physics course. I'll bet it comes up in his Thermodynamics class.
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