(06-15-2016 06:50 PM)Sleepster Wrote:
(06-14-2016 08:39 PM)verbatim1 Wrote: Given that they could have chosen ANY voltage, we must assume that everyone else chose 12VDC BECAUSE it was standard; and then we must then assume that ResMed either had a good reason for 24VDC, or they had a marketing reason.
Why does the grid in some continents provide 240 volts, but in others 120 volts? Why 50 Hz in some and 60 Hz in others?
Things differ, there's no deeper reason, in my opinion.
While the classic joke as to why the US uses half the voltage pressure that Europe uses for mains power is that Americans are pansies who can't handle high voltages, let's never forget that the marketing guys, not the engineers, decide such things.
As Mongo said later, European 230VAC mains have huge advantages over American 110VAC mains with respect to power distribution at the low end, which is why the Germans used the higher voltage (they didn't care about safety as much; they cared about cost). Bearing in mind that everyone has to factor in costs, even in the 110VAC world, the power companies use the highest voltage they can get away with (e.g., tens of thousands of volts) in their grid, and only step it down when it gets close to the final destination.
There is no doubt that the 110VAC mains is certainly safer than a 220VAC mains, although we, in the USA, also have 220VAC power for our stoves and air conditioners.
The point is that the original reason for the USA 110V vs Europe 230V mains was a MARKETING decision, based on cost and safety input, where the Americans opted for safety while the Europeans opted to save costs.
Historically, in the USA, they started with DC voltages, and then (quoting from http://www.school-for-champions.com/scie...rc3BDYPxw)
"With the backing of the Westinghouse Company, Tesla's AC system became the standard in the United States. Meanwhile, the German company AEG started generating electricity and became a virtual monopoly in Europe. They decided to use 50Hz instead of 60Hz to better fit their metric standards".
So, it seems that, given the exact same input, the European executives opted for cost and convenience, while the American executives leaned further toward decisions based on human safety.
As for 50Hz and 60Hz, the differences, while also huge, are less easily decided upon. Mainly, I've been told that the Americans went for less flicker on the bulbs (60Hz being further above the eye's tolerance than 50Hz) while the Europeans again put more weight on cost considerations than on bulb flicker (although the costs difference calculation is more complicated as can be seen in the quoted article due to how the two frequencies differentially affect transformer size and eddy plates).
Both the US and Europe opted for 3-phase power (any number of phases could have been used, but 3 phase was a good compromise for both sides of the pond).
In summary, in Europe, the (German) power company business executives opted to put far more value on saving money than on safety, whereas in the USA the (Westinghouse) executives opted for safety over saving money.
Notice that, just as we have with cpap, the same inputs by the engineers result in different outputs by the executives, who make such decisions after all.
The relevant observation is that the engineers had nothing whatsoever to do with these decisions by the executives. The engineers can build either system easily.
What gets built depends wholly on what the marketing and business executives want built.
Of course, they "ask" the engineers for their opinions, just as they ask the lawyers for their opinions, and the bean counters, etc., but in the end, the engineers are NOT the ones who decide what gets built.
In the case of cpap, the key question is whether there is any direct good reason for the hugely non standard power supplies.
While "reasons" were given (e.g., a litigious society), there is absolutely no correlation provided with those reasons to the power supply decision. For example, if I asked for the difference between ResMed and Philips and someone tells me the ResMed comes in "pink", sure, that's a difference - but it has nothing whatsoever to do with the choice in power supplies.
I haven't yet seen any difference that we, as engineers (I'm a civil engineer, not an EE though) can ascribe to the marketing choice of the hugely non standard power supply.
But I'm an engineer who is as open minded as anyone - so that's why I ask.