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Jas_williams wrote: ↑

Mon Dec 31, 2018 9:33 am

I would expect the conversion from 12v DC to 24v DC to be more efficient than the conversation from 110v/240v AC(I am in the UK) to 24v DC as more heat will be produced in the Rectifier/Step Down transformer than a DC-DC Step up transformer. As we are considering 12V use as that is where power is limited.

Efficiency is awesome. So do we have enough information to answer the question: Do we suspect the difference in kwh using the same setup would be substantial? (Say, more than 10% difference?)

DreamDiver wrote: ↑

Mon Dec 31, 2018 8:00 am

Yikes. Maybe I shouldn't reply late at night. Apologies for confusion.
I use a humidifier. It stays connected and ready to use whenever I use the machine. I use the S9 for usually about 7.5 hours each night. Sometimes it's split into a nap and less time at night. The S9 remains plugged in and drawing power regardless of whether it's on and delivering therapy or sitting dormant. Over the 24 hour period, including the time in therapy and machine dormancy, it used 0.26 kwh.

There is a period of time after the S9 is turned off when the blower runs at extremely low pressure to dry out the tube. The S9 is dormant (idle) when the blower isn't drying out the tube and no therapy is being delivered. It still draws current when idle.

Yes, there is a small load at idle. My point was that the load you are claiming is 5 Watts, which seems rather high given that the advertised load when running at pressure 6 is less than that. When I measure my Dreamstation the idle load is .11 amps (at 12V) or about 1.3 Watts. I believe the discrepancy is a combination of the inefficiency of the AC->DC power brick at low load and known issues with the Kill-A-Watt measuring low power. To quote the Wiki, "Most plug-in wattmeters are not useful for measuring standby power..."
...

DreamDiver wrote: ↑

Mon Dec 31, 2018 8:00 am

CapnLoki wrote: ↑

Sun Dec 30, 2018 9:41 pm

I certainly use the humidifier at home but I never use it when "off grid" ...

This is like full face or nasal. Perhaps debating the point is about as fruitful.

Well, this isn't a philosophical question of which is better, its a matter of how many folks are willing to buy and carry a battery three to five times bigger in order to run humidity. Since the ambient humidity is often high when "roughing it" the discomfort for most folks does not rise to the level of wanting to carry a 60 pound battery. I know a few folks here use humidity but I'm sure its a rather small minority. This point started with the utility of drying the hose, and I would agree the if you're will to have a large battery to run humidity, then you might not mind a bit more to dry the hose (if you feel the need).

DreamDiver wrote: ↑

Mon Dec 31, 2018 8:00 am

The pump was not running at idle (dormant). You may be right about accuracy. It's really better for measuring long-term usage. Hence my wanting to look at it over a week.

If the measurement is inaccurate over a 24 hour period, doing it for a week doesn't help at all! Again - if you're trying to determine the expected load when running off a battery, you have to actually measure the DC current. Measuring the AC current is rather useless. If you're trying to determine the "best practice" when running off a battery, then with 30 years experience living on 12V power I can assure you that if its not running, unplug it!

CapnLoki wrote: ↑

Mon Dec 31, 2018 10:18 am

I know a few folks here use humidity but I'm sure its a rather small minority.

Actually it's the guys/gals who don't use added moisture that are in the minority when talking about cpap users in general.
And according to what I have read along with my own personal informal poll on the subject...more people use a higher than middle range setting than those who use less than a middle of the range setting or none.

Now if you are just talking about the users who like to go off grid and "rough it"....then maybe the numbers of no humidifier use might be a bit higher but a good many of those people roughing it are already people who use minimal to none added moisture anyway.
Maybe I need to do another poll and really irritate the poll haters.

DreamDiver wrote: ↑

Mon Dec 31, 2018 8:00 am

Yes, there is a small load at idle. My point was that the load you are claiming is 5 Watts, which seems rather high given that the advertised load when running at pressure 6 is less than that. When I measure my Dreamstation the idle load is .11 amps (at 12V) or about 1.3 Watts. I believe the discrepancy is a combination of the inefficiency of the AC->DC power brick at low load and known issues with the Kill-A-Watt measuring low power. To quote the Wiki, "Most plug-in wattmeters are not useful for measuring standby power..."
...

I'm reading the numbers off the meter. I'm using an S9, and you're using a DreamStation. They're entirely different beasts, so perhaps the only way to determine how bad the KWEZ is would be to use the same meter to check your DreamStation at therapy and at idle. Alternatively, I could take measurements using standard tools while hooked up to battery. Except I don't have a DC meter that will record realtime actual killowatt hours like the KWEZ does for AC. If I were to measure the DC power needs, I'd still put it before the DC power block required by the S9, right? Maybe there's an inexpensive (~$20 budget) meter that can be connected to between my battery and the power brick for ease of recording realtime kwh.

CapnLoki wrote: ↑

Mon Dec 31, 2018 10:18 am

Well, this isn't a philosophical question of which is better, its a matter of how many folks are willing to buy and carry a battery three to five times bigger in order to run humidity. Since the ambient humidity is often high when "roughing it" the discomfort for most folks does not rise to the level of wanting to carry a 60 pound battery. I know a few folks here use humidity but I'm sure its a rather small minority. This point started with the utility of drying the hose, and I would agree the if you're will to have a large battery to run humidity, then you might not mind a bit more to dry the hose (if you feel the need).

I have a 60 pound battery. I don't carry it around unless it's in the back of the car or truck. I was glad to have it last time the power went out for five days. But I'm not exactly roughing it. The battery sits in my bedroom. I recharge it with AC.

CapnLoki wrote: ↑

Mon Dec 31, 2018 10:18 am

If the measurement is inaccurate over a 24 hour period, doing it for a week doesn't help at all! Again - if you're trying to determine the expected load when running off a battery, you have to actually measure the DC current. Measuring the AC current is rather useless. If you're trying to determine the "best practice" when running off a battery, then with 30 years experience living on 12V power I can assure you that if its not running, unplug it!

I'm reading the numbers off the meter. I assume they're accurate to some degree or KWEZ wouldn't be so popular. For the S9, a power block is required regardless of AC or DC. DC to DC conversion is more efficient. According to physicsbob who wrote about this back in 2010 on cpaptalk.com, most of the AC power blocks for CPAP are about 95% efficient so they should give you a reasonably good clue as to how much power they require using a killawatt EZ.

Pugsy wrote: ↑

Mon Dec 31, 2018 10:51 am

CapnLoki wrote: ↑

Mon Dec 31, 2018 10:18 am

I know a few folks here use humidity but I'm sure its a rather small minority.

Actually it's the guys/gals who don't use added moisture that are in the minority when talking about cpap users in general.
And according to what I have read along with my own personal informal poll on the subject...more people use a higher than middle range setting than those who use less than a middle of the range setting or none.

Now if you are just talking about the users who like to go off grid and "rough it"....then maybe the numbers of no humidifier use might be a bit higher but a good many of those people roughing it are already people who use minimal to none added moisture anyway.
Maybe I need to do another poll and really irritate the poll haters.

I'm sure that when at home most go for the comfort of humidity - I certainly do. I usually use a mid setting so I won't run out. And I often use a 12 gallon console humidifier to keep the bedrooms up at 30% RH or better. My particular "roughing" location is almost always 80%+ so I don't need the tank even if it were physically possible (there's no place to put it in my bunk!). I normally travel to humid climes so its a tossup as to whether I take it on trips - more often then not I've regretted the extra baggage. My trips this year have been DC, FL, and NOLA and I haven't taken the tank for any of these trips.

Your point that those who "rough it" are more likely to not use humidity at home seems provocative! There may be some small correlation but I doubt a generalization is warranted - maybe it is time for a poll, as much as I hate them!

CapnLoki wrote: ↑

Mon Dec 31, 2018 12:13 pm

Your point that those who "rough it" are more likely to not use humidity at home seems provocative! There may be some small correlation but I doubt a generalization is warranted - maybe it is time for a poll, as much as I hate them!

Just seems to me like when I see people talking about camping without humidifier that I often see "but I use a low setting at home" kind of comment.
Also they don't always tell us where they are choosing to camp. I just got back from Vegas...crap that place is dry. Big difference camping out there in the desert and on your boat without added moisture.

I do feel particularly annoying today though...but man composing a poll like this and doing it right and being limited to 10 options is a lot of work...not feeling up to doing all that work at the moment but do feel up to irritating some people.
We will see later who wins out...my annoying self or my lazy self.

Conversion>>>conversation.
Spell-INcorrect strikes again!
(Picture programmers rolling on the floor, laughing their butts off)

DreamDiver wrote: ↑

Mon Dec 31, 2018 10:01 am

Jas_williams wrote: ↑

Mon Dec 31, 2018 9:33 am

I would expect the conversion from 12v DC to 24v DC to be more efficient than the conversation from 110v/240v AC(I am in the UK) to 24v DC as more heat will be produced in the Rectifier/Step Down transformer than a DC-DC Step up transformer. As we are considering 12V use as that is where power is limited.

Efficiency is awesome. So do we have enough information to answer the question: Do we suspect the difference in kwh using the same setup would be substantial? (Say, more than 10% difference?)

Most reports of the DC-DC converter claim 90%+ efficiency. And most AC power bricks are labeled "Class V" which means 85%+ efficiency when running at the full rated output. Unfortunately none of this informs us about the low current efficiency or "vampire" drain which could be much higher. If I had to guess, I'd say the DC-DC converter stays fairly efficient at low loads, but the AC brick drops of severely, to 50% or maybe much lower at low power.

Inverters are the same, advertising 90% but often more like 70% going down to 10% at low power.