Per Resmed - powering an S9 machine with an inverter

[ignorant1]

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NOTE: If you are seeking a definitive answer on this subject, please read towards the bottom of this thread
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I know there is much concern about frying the Resmed units due to their unique power requirements. This subject has been beaten to death already, but there’s simply way too much to read through about batteries, converters, & power supplies. Perhaps we can provide a single thread with a simple answer?

Scenario: My Resmed S9 (Adapt / ASV) series clinician’s manual lists the power consumption (with the 90-watt “power brick”) as typically being 70 watts.

I would like to use a power inverter that’s rated for 150 watts continuous output (with 90% efficiency @ ½ of it’s rated load capacity, i.e., 75 watts). It has a “modified sine-wave” output. (Actually, the manual states “Perfect modified sine wave” – but who knows what got lost in translation.)

THE MAIN QUESTION: Can the Resmed power brick be used on a modified sine-wave converter, or do I run the risk of frying either the power brick or the S9?

Thanks in advance for any knowledgeable replies!

P.S. - I know that this is an inefficient way to do it – with the double losses of power conversion from 12vdc to 120vac, and back to 24vdc, but an “official” Resmed converter is ridiculously expensive.

[archangle]

It's going to be real hard to get an authoritative answer. There may be someone who's run theirs on a MSW inverter for years with no problem. That doesn't mean that one out of 3 MSW users will eventually fry their S9 machine.

Square wave devices tend to generate spikes on the edges of the square waves. A MSW inverter is really a modified SQUARE wave inverter, not a modified sine wave inverter. Some are better than others, but some put out spikes.

I talked to my friend who does solar power and uses inverters all the time. He says that a lot of the "pure" sine wave inverters are junk, fail a lot and generate a lot of trash on the output, too.

I can tell you that, usually, an electronic device will see a MSW inverter output as being a lower than normal voltage, rather than a too high voltage. This makes it a little less likely to do damage, perhaps. It will tend to see electrical noise on the input voltage, which can cause problems.

[GumbyCT]

P.S. - I know that this is an inefficient way to do it – with the double losses of power conversion from 12vdc to 120vac, and back to 24vdc, but an “official” Resmed converter is ridiculously expensive.

I waited for all the experts and double-secret Resmed operatives to respond but nothing.... so here goes my thoughts.

IF it were me, I would being making my own cable or buy a machine that I could make a cable for. Find a manufacturer that has more reasonable prices.

So what did you do Gumby?
I acquired a Resmed S8 Escape to experiment with. This S8 has a coaxial DC connector which makes me think the other S8's would also have the same connector. And just as I suspected the smoke and mirrors were lifted.

HOW did you do it Gumby?
After a lot of thought AND sleepless nites - I took the DC cable I made for my Respironics with the Radio Shack Adapta Plug and turned it backwards so the center pin (tip) was negative, plugged it into the S8 and just as I suspected the Resmed S8 powered on. Not hard. Since it's not a bilevel machine I did not sleep with it and I have no use for this machine except to dry a hose (which I don't do btw).

While I understand this is an S8, I think there are still plenty of S8 machines in use that people could make their very own DC cord for with Radio Shack parts.
viewtopic.php?f=1&t=53672&p=498461&hili ... ck#p498461

So the S9 has 3 pins - we know one is positive and one is negative while I am not positive where the 3rd wire goes just yet neither am I convinced yet that it is needed.

As for All this voodoo about a Resmed circuit to tell when the battery voltage drops, I guess there are people who don't realize that electronic components have a voltage tolerance and when the voltage drops they cease to function - so that Resmed circuit is not needed.

As for the Resmed spike suppression circuitry - I wouldn't expect voltage spikes of ANY significance when connected to a DC battery as in a car jump starter.
viewtopic.php?f=1&t=64943&p=606095&hili ... ry#p606095

So what magic do you need if you make your own Resmed DC cable?
I am surprised someone with an S9 is not working on this magic cable box. Didn't DSM do some work on this?

JMMO
So bring on the naysayers.

[rested gal]

I know there is much concern about frying the Resmed units due to their unique power requirements. This subject has been beaten to death already, but there’s simply way too much to read through about batteries, converters, & power supplies. Perhaps we can provide a single thread with a simple answer?

You're absolutely right about "way too much to read through about batteries", etc.

Guess what?

Your topic just now got added to the "way too much" place!

LINKS to Battery operation, camping, power outage
viewtopic.php?t=9682

Yes, you can hope for a simple answer in the thread you started. That would be what I'd do, too!! Even I wouldn't want to try to wade through all the topics I put in links for!!

[ignorant1]

Well, I DO appreciate everyone's input... Too bad we can't get an authoritative consensus together on this subject.

To make matters even more confusing, I looked at CPAP.com and they list a "Modified Sine Wave" power inverter "manufactured by Resmed" - but the picture shows a unit made by "Tripp-Lite". Link: https://www.cpap.com/productpage/resmed ... erter.html - Must be a mistake, no?

P.S. - A special thank you to Rested Gal for that comprehensive list of links. Wow. I will definitely be referring back to that to do some research in the coming weeks. (And it will probably take MONTHS to wade through all those threads! ) Either that, or I'll eventually just bite the bullet and buy the Resmed DC to DC converter. It's one thing to fry an $800 S9 auto, and another thing to fry a S9 Adapt (ASV) machine that costs five times as much. (And why the same basic architecture costs so much more is a matter for a whole 'nother thread.)

[billbolton]

Well, I DO appreciate everyone's input... Too bad we can't get an authoritative consensus together on this subject.

See..... http://www.resmed.com/us/assets/documen ... lo_eng.pdf

Cheers,

Bill

[archangle]

Very interesting. ResMed says an S9 with humidifier can be used with a MSW inverter of 150 W.

Most other ResMed CPAP can be used with an MSW inverter, but NOT the humidifier. ResMed says a MSW inverter will damage the humidifier.

If you've got an inverter, and it doesn't say otherwise, it's probably a MSW (Modified Sine Wave) inverter.

[Guest]

The S9 humidifier runs from the 24V. All previous ResMed humidifiers have run from mains. That's the critical difference.

The S9 and H5i humidifier can safely be used with a 150W modified sine wave inverter.

[ignorant1]

YES! We FINALLY have a definitive answer!
(Much thanks to BillBolton for the link!)


The answer lies in Resmed's own publication as linked above by BillBolton:

All S9 series units CAN be run from a MSW inverter - PLUS you CAN run the H5i humidifier (as fitted to the S9's) using the inverter as well.

You CAN run an S8 series unit from a MSW inverter, but you CAN NOT run the ANY of the humidifiers that attach to an S8 while using a MSW inverter.

That's it. Pure & Simple!

I hope this helps others in the future...

[rested gal]

Glad you got a definitive answer.

If everyone who wanted a sticky placed for something that he/she felt was of the utmost importance, there might be several hundred stickies to pick through.

Failing a sticky for this particular question/answer, what you could do is edit your original topic-starting post. Edit it to change the subject title to something that would attract the attention of others with the same concern. Perhaps a title like:

ResMed instructions - how to power an S9 machine with an inverter

or...if that's too long, try:

ResMed instructions - powering an S9 with an inverter

[ignorant1]

Great idea RestedGal! And done...

[rested gal]

Cool. I'll change the title on my battery links page.