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My battery backup setup
(06-15-2016, 01:32 PM)TiredInSoCal Wrote: I don't have personal experience with the S8, but from what I know the S9 and Air10 actually have the same power requirements. Changing the plugs and therefore the adapters required is ridiculous. It reminds me of when cell phones all required different power adapters - at least the same manufacturer generally kept the same plug from phone to phone.

The standard S-8 was typically a plain 12 V system that would run fine from any old functional 12 V battery. They even used a standard 5.5x2.5 mm plug, IIRC. The kink was that the Resmed folks didn't follow a more standard center pos, outer gnd scheme wiring their connectors and DC sockets. They made the outer barrel of the connector the pos side and the protected inside of the barrel the gnd side. Again, I believe, to make folks buy their backwards wired DC power cable. If you used a standard wire, it would likely brick the unit and you would have to not only buy the cable, but a whole new machine (YAY! More sales for Resmed!). Absolutely NO reason to do that except to sabotage anyone with the temerity to use their own cheap cord. That is one prime reason that I believe that their shenanigans to this day have nothing to do with design or performance - just screwing the folks that buy their product and feed their families.
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My S8 has a built in AC supply and a 24 Volt DC input.
Photo of bottom plate... (slightly cutoff the power rating)
[Image: 13SEPT2013%20004.jpg]

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That's not an S-8 CPAP or APAP, though, now is it? I know the VPAP and Bi-PAPs may have been 24 V, but in the overall scheme of things, I think those are a relatively smaller percentage of the overall PAP world...

Time to go set up a poll.

OMMOHY
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True, it is a VPAP S.

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(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.
Sleepster
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240VAC was adopted in places like Britain to save copper. You can deliver the same power (Watts) with half the weight of copper.

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Yes but not as sinister as some might think. 99.9% of the customer base just use the adapter supplied with the unit and never does anything else. They don't even offer an automatic switch over (I don't think) from AC to battery that they supply, you have to wake up and change cables.

There are tons of reasons why they may have changed the connector, price, availability, reliability, safety requirements, or new engineer that liked the new one better.

(06-15-2016, 01:32 PM)TiredInSoCal Wrote:
(06-15-2016, 12:57 PM)PoolQ Wrote: Back to the thread-a one time purchase of an $85 converter is fine with me.

I agree. However, what is a problem is when they change what kind of a converter you need for each model. For example, going from the S8 to the S9 to the Air10 you need a different converter.

I don't have personal experience with the S8, but from what I know the S9 and Air10 actually have the same power requirements. Changing the plugs and therefore the adapters required is ridiculous. It reminds me of when cell phones all required different power adapters - at least the same manufacturer generally kept the same plug from phone to phone.

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(06-15-2016, 08:43 PM)PoolQ Wrote: ....or new engineer that liked the new one better.

I've been there. Some new engineer is bent on using the latest processor in a satellite system; and I have to tell 'em NO. Your part will be dead at 10 kilorads; and the dose-depth kernel is asymptotic at 25 kilorads. (i.e. -- no amount of shielding will get the part exposed to less than 25 krad over mission life; and it'll be dead at 10 krads.)

Admin Note:
JustMongo passed away in August 2017
Click HERE to read his Memorial Thread

~ Rest in Peace ~
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(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.
Hi Sleepster,

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...5rc3BDYPxw) "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.

REFERENCES:
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I was in the Remworks DME yesterday to pick up some new nasal pillows, and commented about the difficulty of using a Resmed on battery. The RT on duty suggested, well just buy the battery, pointing to a display. I looked at the packaging, and it was a 12 volt battery, so I scoffed, "So the battery you sell is $350, and I would still need an expensive 12V-24V up-converter adapter.

The good news is, I confirmed I'm no longer monitored for compliance, and can use my PRS1 machines when camping. Problem solved.
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