Resmed CPAP on 12v battery

Hi

I'm a new user of ASV and also do a bit of camping etc so looked for some info regarding battery packs etc and seen a few questions on here but no real definitive answers so here's my findings. I'm an electronics tech so not meaning to tread on any toes if anyone has previously posted this, but not from what I can find.

All my info is regarding the Resmed S10 ASV but would relate to any 24v CPAP. For 12v systems the DC converter is not needed but the battery power would be the same. I used 12v batteries for ease of finding at a local camping/electronics shop and not have to tie 2 together to make 24v.

So regarding battery backup for a power outage. The easiest solution would be to purchase the likes of a CPAP travel battery (not mentioning brands as I don't think that's allowed on forums). These simply take the mains from the Resmed PSU and then from the pack supply to the machine, in the event of a power blackout the battery takes over automatically and goes back to mains when power is restored. Simple, small and will run a machine with humidifier etc for at least 3 hrs, so should last most blackouts, otherwise if noticed you could turn off the humidifier and run for 8hrs+. or overnight camping with no humidifier. FYI these are 95Wh or approx 4Ah

Now the camping and serious off grid users:
You could use a resmed 12v converter approx $100 battery size would be the same or

What I have done is grab a CPAP battery to S10 cable, cut the plug to the machine and wired the other end to a 12-24v DC-DC converter. These are available on Ebay for <$30 (I got a 12A model, overkill as Max current found was <6A and the original PSU is rated for 3.75A @24v so even 8A would be fine)
Then otherside to a 12v battery, a protection device can be inserted also to ensure you don't over discharge the battery and cause damage.

I also put an inline meter to check the current, power and ultimately AH readings overnight to see what size battery would then be required, my settings for ASV are 6 EPAP and average 15 IPAP. But from what I have found the power use on the air pump is negligible on it's own so 10cmH2o and 20cmH2o not much different in usage.

Without the Humidifier the usage on a 12v battery was:
32 Wh overnight 8hrs = 4 Wh per hour
3.1 Ah overnight 8hrs = 0.4 Ah per hour
Peak current = 1.7A
So a 7Ah 12v gel cell battery (aka alarm backup battery) with the DC converter would be suitable for 2 nights @ 8 hrs without charging. Makes sense as the travel packs purchased last 1 night without humidifier @4Ah


Humidifier & heated tube running, with the same formulas and averaging the auto setting and humidity 4 and tube temp @27 C (so normal home use) over several nights.
I'm in Australia so the nights are not cold so I'm sure colder climates may need more power.
17Wh per hour of use
1.4Ah per hour of use
i.e a 11Ah usage over 8hrs
So a 40Ah deep cycle battery with the DC converter would do for 2 days uncharged.
I tested one and ran one night with 60% left so confirms this. this would be the battery I will take camping as I have a 180W solar panel to charge every day but in case one day is a little overcast I have some emergency power. If bad weather sets in and I can't charge that well, I can turn the humidifier and heated tube off and get over 1 week with no charging.

It may be as clear as mud for some but I hope it helps. I have attached photos of the setup, test setup and battery tested etc.

Forum member Cap'n Loki is the expert here and has contributed lots of info on how to rig what battery in which way to achieve what results depending on your situation - everything from camping to truck driving. Do a forum 'search' to see if your ideas match up.