[Equipment] ResMed Airsense 11 battery backup

[ScottZZZ]

Best guess is the voltage (using older battery) is dropping below 11.4V under load, which is where the AirMini DC-to-DC Converter shuts down. An older battery may still have capacity for other devices, but if it drops below 11.4V under load then the AirMini adapter will shutdown.

[davidgr]

Best guess is the voltage (using older battery) is dropping below 11.4V under load, which is where the AirMini DC-to-DC Converter shuts down. An older battery may still have capacity for other devices, but if it drops below 11.4V under load then the AirMini adapter will shutdown.

Electrical mystery. First of all, the good news. In my at-home experiment, I have just gotten through 4 nights in a row with my cpap powered by the airmini dc to dc converter and a 100 amp hour deep cycle marine battery. If it lasts another night, the battery will get me through my 5 nights of camping coming up in early June in the Cal Redwoods.

Here's the mystery. If I first attach the clips to the battery and plug the converter into the cpap secondly, the light goes out on the converter and the cpap does not go on. BUT, if I plug the converter into the cpap first, and secondly attach the clips to the battery, the cpap works. Why would that be? (This could be the reason that some folks think the airmini adapter won't work. FYI for you here in this post).

[ScottZZZ]

@davidgr

Very interesting finding -- and very strange.  No idea why the connection order would matter.

For what it is worth, the converter's User Manual DOES specify connecting the cpap to the converter first, and then connecting the converter to power.  So maybe what you are seeing is by design (but I still have no idea why).

When I get a chance, I will do some testing to see if my converter & cpap behave the same as you describe for yours.  I am normally using mine in conjunction with a power supply, sort of like a UPS for power outages, so both ends are already connected when switching to battery. The few times I have used it on battery alone, I don't remember which side I connected first. 

In any case -- Good to hear you found a way to make it work reliably and get the runtime you need for your trip!

[ScottZZZ]

@davidgr

I tested my setup last night to see if the connection sequence made any difference.

I connected the converter to the battery first, then connected the AS11. It booted up normally (splash screen, then reading SD, then main menu). Started up the AS11 (with humidifier and heated hose active) and it ran fine.

I repeated that twice more, leaving the AS11 disconnected for about 30 seconds each time. No problems, it booted up fine and the converter's LED stayed green each time. Then I tried the opposite sequence, connecting the AS11 to the converter first and then connecting the converter to the battery. No problems with that sequence either.

Not sure why yours and mine would act differently in this regard. My battery was fully charged (gel cell, 13.5V), so voltage may still be in play if your battery's voltage curve reacts a little differently when the AS11 starts. But with a sample size of (2), it's hard to draw any conclusions.

[davidgr]

@davidgr

I tested my setup last night to see if the connection sequence made any difference.  

I connected the converter to the battery first, then connected the AS11.  It booted up normally (splash screen, then reading SD, then main menu).  Started up the AS11 (with humidifier and heated hose active) and it ran fine.

I repeated that twice more, leaving the AS11 disconnected for about 30 seconds each time.  No problems, it booted up fine and the converter's LED stayed green each time.  Then I tried the opposite sequence, connecting the AS11 to the converter first and then connecting the converter to the battery.  No problems with that sequence either.

Not sure why yours and mine would act differently in this regard.  My battery was fully charged (gel cell, 13.5V), so voltage may still be in play if your battery's voltage curve reacts a little differently when the AS11 starts.  But with a sample size of (2), it's hard to draw any conclusions.

Good question, and interesting result for you as compared to my experiment.  Observation: The battery I used is my old one. That battery was used once per summer for several years and hardly charged in between. (Yes. I really need to camp at least twice per summer). Clue? When my AS11 starts, the little screen has normal brightness for one half second and then the brightness halves. Everything else works normally. Note: I have not been using the heated hose or humidification.

I get back to you with the new experiment; use of the new deep cycle battery I purchased recently. Perhaps that one will behave differently. Meanwhile, I want to see how many nights the old battery actually gets me through. So far, 5 full nights. Not looking forward to the moment in the middle of the night that I realize I'm not breathing, but I'm willing to sacrifice myself (so to speak) for science. : >)