Resmed Airsense 11 - AC/DC adapter?

Scott_G wrote: ↑

Tue Jan 25, 2022 10:48 am

It allows smaller gauge wiring, and lower motor mass (smaller windings) that reduces inertia and allows faster response to RPM changes.

I understand the logic of voltage vs wire gauge, etc. I just don't think that was the resmed reason.

Scott_G wrote: ↑

Tue Jan 25, 2022 10:48 am

It wouldn't be an issue if we all had 24v batteries laying around. The ubiquity of large capacity 12v batteries is the only reason we find 24v operation "inconvenient". I've given some thought to wiring two 12v AGMs in series, reverse-engineering the pinout voltages on the DC/DC adapter plug and wiring up a straight cord. I may do that the next time my 12v battery is due for replacement.

Agreed it wouldn't be but that isn't the case and some how resmed didn't know that?

IF you do that little adapter project I would be interested.

Scott_G wrote: ↑

Mon Jan 24, 2022 1:21 pm

In my tests, the standard AC/DC converter in combination with a sine-wave inverter was about 64-70% efficient, while the DC/DC converter was about 72-78% efficient.

Interesting, I think I've read that the standard S9 (and presumably air 10) DC/DC converter is 90%+ but I might be imagining that, or that may be 'claimed' vs 'real world'.

palerider wrote: ↑

Tue Jan 25, 2022 3:19 pm

Interesting, I think I've read that the standard S9 (and presumably air 10) DC/DC converter is 90%+ but I might be imagining that, or that may be 'claimed' vs 'real world'.

I haven't seen any efficiency spec from Resmed for the AS11 DC/DC converter. Doesn't seem like the kind of detail they would publish but would love to see it. Also, the efficiency of most boost converters varies with the difference between input and output voltages -- so with a constant 24V output, you'd typically see much higher efficiency when the input was 23V than you would when it was 12V.

I honestly expected better... But repeated tests gave me the same numbers. I did look at (2) other data points to "sanity check" my 72-78% finding:

• Stamped on the dc/dc converter, it claims a max Input of 12v@8A (96W) and max output of 24v@2.71A (65W). That only equates to 67% of input power making it to the output. Now those are "maximum rated" safety values, not "typical usage", so don't directly reflect efficiency -- but they do imply some power loss in conversion.
• I have the adapter in open air, sitting on a metal surface. Despite that, it gets quite warm during use. Not hot, but pretty warm. I haven't measured the heat output, but to my totally unscientific "touch test" it feels like the heat you'd get from a 10-15W light bulb. I know the actual consumption of the CPAP (with my pressures, humidifier ON, heated hose ON) is about 45W, so 10W lost to heat would equate to a 22% loss (or 78% not lost).

Those points seemed to validate what my DMM was telling me, so I accepted the numbers. Again, just approximations as I didn't do extensive testing over a range of pressures/settings, but I think that 72-78% is at least "in the ballpark".

Scott_G wrote: ↑

Tue Jan 25, 2022 4:45 pm

I honestly expected better...

Indeed, that's a disappointing efficiency level.

Thank you Scott_G! I read all of your info and it is great! My spouse uses the Airsense 11and on a recent RV trip, couldn’t use the machine as we forgot the portable battery pack with the inverter and AC plug. Plus, there just isn’t enough room for a large portable battery pack with a plug-in inverter on the shelf of the RV. I have the Airsense 10 (spouse used to have that model until it broke) and can use a 12 volt adapter with a small lithium battery. Now, thanks to you, we will buy the AirMini DC adapter.

No idea what kind of RV you have but I would think there would be room right on the floor near the bed?

I have used a couple of UB-1270 alarm system batteries wired in series to give me 24vdc. This gave me a couple nights of service, with no humidifier. I only needed it to last two nights so not sure if it would last longer. The plug was from a old power supply I had laying around. The two batteries cost me $40. A poor mans solution that requires some wiring.

Aretino wrote: ↑

Mon Jan 31, 2022 11:55 am

I have used a couple of UB-1270 alarm system batteries wired in series to give me 24vdc. This gave me a couple nights of service, with no humidifier. I only needed it to last two nights so not sure if it would last longer. The plug was from a old power supply I had laying around. The two batteries cost me $40. A poor mans solution that requires some wiring.

I wonder if the efficiency is any better using 24Vdc?

Using a 24V source and straight wire harness (no converter) would be near 100% efficient, with the only loss being to resistance in wire/connector. The challenges would be sourcing the connector (it appears to be proprietary, so might have to cut one off a Resmed supply), determining the pinout, and determining if there are any other voltages or digital signals exchanged between the supply and machine. As I recall, the AS10 needed a secondary voltage (3v?) on one pin, for example. And some kind of "low voltage cutoff" might also be needed to protect the AS11, depending on how it reacts to low voltage as the batteries run down.

Using a 24V source with the Resmed DC/DC adapter (I think it will accept anything between 11.5V and 29V on input side) would likely be much more efficient than using a 12V source, but I can't say by how much.

Scott_G wrote: ↑

Mon Jan 31, 2022 12:27 pm

And some kind of "low voltage cutoff" might also be needed to protect the AS11, depending on how it reacts to low voltage as the batteries run down.

My thinking is that the device will turnoff when it doesn't get the voltage it needs.

Scott_G wrote: ↑

Mon Jan 31, 2022 12:27 pm

The challenges would be sourcing the connector (it appears to be proprietary, so might have to cut one off a Resmed supply)

Cutting the connector off would likely be the fastest way to access the correct connector. If one were handy enuff they would consider using more connectors on this new pigtail and on the old AC adapter to move the pigtail back n forth if needed.

Just some thoughts.

SleepGeek wrote: ↑

Mon Jan 31, 2022 8:18 pm

My thinking is that the device will turnoff when it doesn't get the voltage it needs.

Maybe. Or maybe it will try to keep running, overheat and damage itself. Unknown. The fact that the DC/DC converter has a specific input voltage shutdown could imply a safety shutdown based on output voltage. I’m certainly not going to test it on MY machine.

SleepGeek wrote: ↑

Mon Jan 31, 2022 8:18 pm

would consider using more connectors on this new pigtail and on the old AC adapter to move the pigtail back n forth if needed.

That’s a great idea.

Scott_G wrote: ↑

Mon Jan 31, 2022 8:42 pm

Maybe. Or maybe it will try to keep running, overheat and damage itself. Unknown. The fact that the DC/DC converter has a specific input voltage shutdown could imply a safety shutdown based on output voltage. I’m certainly not going to test it on MY machine.

Your car certainly won't/doesn't start when the battery is low nor does it damage any of the electronics and todays cars are loaded with electronics.

I can't think of one DC powered device that will continue to run when voltage gets low much less overheat and damage itself. Can you point me to one?

We are not talking about refrigerators or Air Conditioners here right?

SleepGeek wrote: ↑

Mon Jan 31, 2022 10:24 pm

I can't think of one DC powered device that will continue to run when voltage gets low much less overheat and damage itself. Can you point me to one?

I can’t fathom why you want to argue this, particularly from a position based on lack of factual evidence. Without knowing what the Resmed engineers considered in their design, nobody can say what they did or didn’t protect.

This cpap machine is not a simple mechanical device, but rather an electronic device with multiple semiconductors, sensors, and semiconductor-controlled loads (dc motor and two resistance heaters). Under-volted motors can draw current higher than designed, which can damage them and/or the components feeding them. Insufficient voltage to a mosfet gate can change is operating state, causing unintended current draws on the controlled loads. Insufficient voltage to a pressure sensor may cause an inaccurate reading. Etc. These are well-known, basic characteristics in electronics design. For more examples and failure scenarios, please consult some electrical engineering texts or use Google. I’m not here to teach electronics theory or perform Google searches on demand.

The bottom line is that some electronics devices can be damaged by low voltage, while many are not. We simply don't know the internal design of the AS11 or how Resmed tested, so applying less voltage than specified by Resmed carries a non-zero risk of damage.

Feel free to test under-voltage conditions on your own AS11. I have done enough electronics testing to know it isn’t a good idea without knowing whether the engineering design considered and protected for it. I am not going to risk my personal cpap to find out.

Please report back with your test results.

Scott_G wrote: ↑

Mon Jan 31, 2022 11:04 pm

Please report back with your test results.

So you make a comment and want me to confirm its accuracy?

Scott_G wrote: ↑

Mon Jan 31, 2022 11:04 pm

Maybe. Or maybe it will try to keep running, overheat and damage itself.

hsnopi wrote: ↑

Thu Apr 21, 2022 6:39 am

Thanks for all the help. I watched the voltmeter. While it is sitting the battery is 13.4v but when the cpap is on it drops to 8.5. Even though it is an 8Ah battery it still drops that low. I'll play with it more later.

Airsense10 battery turns off after 3 minutes
https://www.cpaptalk.com/viewtopic/p141 ... l#p1410106

Scott_G wrote: ↑

Mon Jan 31, 2022 11:04 pm

This cpap machine is not a simple mechanical device, but rather an electronic device with multiple semiconductors and semiconductor-controlled loads (dc motor and two resistance heaters for sure).

You are right the digital components control the higher current draw components.

(Asking for your help again.)
Show me one digital component that continues to run (work) with an under voltage?

Maybe this will look familiar to you?

SleepGeek wrote: ↑

Mon Jan 31, 2022 10:24 pm

Your car certainly won't/doesn't start when the battery is low nor does it damage any of the electronics and todays cars are loaded with electronics.

I can't think of one DC powered device that will continue to run when voltage gets low much less overheat and damage itself. Can you point me to one?

So I did ask for help from YOU validating a claim YOU made...
and YOU want me to run down a rabbit hole that isn't there?

I thought you were a sensible person and I guess I was wrong.

Sorry, I'm not able to help confirm your theory.

NOW I think you are just trying to scare people who don't understand electronics.

Please report back with your results of highs too high and lows too low
or is it highs too low and lows too high?
It's a logic 1 or a 0 there is no in between.

That was certainly an incoherent mess. Congrats!

I have said we simply don’t know whether the AS11 design includes low voltage protection or not, and without that knowledge or testing we cannot predict how the AS11 will react. It could malfunction, produce incorrect pressures, or be damaged; or it might just shut down gracefully. We simply don't know unless it is tested. I already provided ample examples of how insufficient voltage can adversely affect various electronic components; you just chose to ignore those or didn’t understand them. Your insistence that an AS11 must have identical design and behavior as your automobile is just plain silly.

What you have claimed - with zero evidence - is that the AS11 absolutely cannot and will not be harmed by applying voltages below Resmed’s specification. Proving your claim is your responsibility, not mine.

If you just want to keep arguing your opinion with no facts or test data, please find someone else to play that game.