24 Vdc ?

[Lucid Moments]

I go to the track regularly and up until recently I have been an official with the organization (NASA-SE) so they provided me with a hotel room. I got tired of trying to work and track at the same time so I have started instructing instead. Downside is that I no longer get a free hotel room. I have started sleeping in the trailer in good weather to cut costs which works out pretty good in the Southeast. Problem is I have sleep apnea so I have to have power for my cpap and trackside power is not always reliable. I have been running an inverter off a deep cycle battery but the inelegance of that bugs me. My cpap machine's power supply says it supplies 24V and 3.75 amps.

What is the best way to get power to this thing when I am off grid? My initial thought is to just get another 12V battery and wire them in parralel. Source a plug that will fit and voila. But my knowledge of electrical stuff is pretty limited so I thought I would check with the hive mind.

Any thoughts are welcome and any input appreciated.

 

[Mr_fixit]

2 12 volt batteries in parallel get you 12 volts. You want them in series.

 

[Lucid Moments]

2 12 volt batteries in parallel get you 12 volts. You want them in series.

Sorry, brain fart. Yes in series. Question still remains is that my best solution.

 

[theoldwizard1]

ResMed Airsense 10 is a common CPAP. They do sell 12V power supplies. Check with your manufacturer.

 

[The Cobbler]

assuming your machine is DC volts, (wired in series as mentioned above) would work

 

[quickfarms]

Inverters are not 100% efficient

What else is running off of the existing 12v battery?

Do you have a generator to charge the battery?

When running two 12v batteries in series to get 24v you can not take large 12v loads off of one battery without risking overcharging the other battery.

Charging a cell phone is not an issue

They do make 24v to 12v power supplies

Without knowing all of the details your best bet maybe two matches 12v batteries in parallel and a 12v power supply

 

[Lucid Moments]

Inverters are not 100% efficient

What else is running off of the existing 12v battery?

Do you have a generator to charge the battery?

When running two 12v batteries in series to get 24v you can not take large 12v loads off of one battery without risking overcharging the other battery.

Charging a cell phone is not an issue

They do make 24v to 12v power supplies

Without knowing all of the details your best bet maybe two matches 12v batteries in parallel and a 12v power supply

Almost nothing else running off the existing battery except as you supposed charging a cell phone. I sleep in the trailer I don't do anything else there. A good cooler keeps my beer cold so no fridge, and lighting is handled by a rechargeable lantern that lasts all weekend (maybe an hour all told).

Ideally I would not need to charge the battery for the weekend, but if I do I can take it out and charge it for the day no issue.

 

[jdm5]

I’d refer you to cpaptalk.com - this thread has a ton of info specifically for powering cpap’s off grid

 

[dogdog]

Might be better if you go get an buck boost converter and either by guesstimate or estimate or direct measuring the draw of your CPAP... then get the boost converter with appropriate rating to boost your 12V to 24V... and buy TWO batteries to put in parallel... then a solar panel to recharge them during the day. why 12V... solar for small scale stuff is more common with 12V unless 24V is common.. ...Deep cycle batteries. JMO...

so if your device is 24Vdc @3.75AMP. expect your 12V to draw about 8.5AMP with the boost convert at about 90% typical efficiency.... or you can go nuts and calculate it down to the mA..



https://cpapsupplies.com/blog/power-cpap-rv/

 

[rlitman]

ResMed Airsense 10 is a common CPAP. They do sell 12V power supplies. Check with your manufacturer.

I just looked at the supply on my ResMed Airsense 10, and it says 90W, 24V, 3.75A. There are DC-DC converters that will run this machine off a 12V battery. Like this:
https://www.amazon.com/dp/B07VV231SJ/?tag=atomicindus08-20

My older ResMed S9 had a proprietary plug, but inexpensive 12V adapters for that exist too. Knowing what model you actually have will help us help you quite a bit.

Keep in mind that most of that wattage is consumed by the humidifier. If you're not needing a humidifier (and heated hose to go with it), you don't need to budget for a battery that can sustain 90W.

ResMed actually has a guide on this:
https://document.resmed.com/documents/articles/198103_battery-guide_glo_eng.pdf

It's interesting to see how pressure changes the wattage. The chart on page 7 for DC-DC converters shows a good comparison. An AirSense 10 set to 10 without humidification requires a 12Ah battery to get through a night, whereas the same machine with humidifier and heated hose will require 60Ah. So, 20% of the power goes to the machine, and 80% goes to humidification.

For comparison, they show an inverter option for my S9, which would need a 97Ah battery for the same setting of 10 with humidification. i.e. they're assuming that DC-DC is twice as efficient as DC-AC-DC, which is about right (if you have an ideal inverter; it can be significantly worse too).

 

[jeepxj]

have you considered something like a jackery? pretty slick all in one solution. can be used for otherstuff as well.

https://www.jackery.com/products/explorer-240-portable-power-station?variant=19479246864471

 

[rlitman]

have you considered something like a jackery? pretty slick all in one solution. can be used for otherstuff as well.

https://www.jackery.com/products/explorer-240-portable-power-station?variant=19479246864471

Even if you do that, drawing off of the 12VDC port will get you significantly longer run-time between charges than using the 120VAC output.

 

[Lucid Moments]

This kind of stuff is why I love this forum.

My machine is a ResMed S9 and I do not use a humidifier. Tried one when I was first diagnosed and it didn't seem to make much difference.

I never thought about a 12V power adapter specifically for the machine. I don't know why I hadn't because it is an obvious solution. Found one on Amazon and have already ordered it.

The battery I got for free is a NAPA commercial type 31. I don't remember the exact model #, but I am going to see if it will run for two nights at the track this weekend. I have another battery I am going to take with me this weekend just as a backup

 

[d33pt]

I built a 24v battery from recycled EV batteries. It's 7s lithium 1.5kwh. It runs my camping fridge for 4 days. Something like that would work great for your CPAP and it can run natively without any wasteful converters. You can also solar charge it too, or charge it off the alternator when your car is running.

 

[rlitman]

This kind of stuff is why I love this forum.

My machine is a ResMed S9 and I do not use a humidifier. Tried one when I was first diagnosed and it didn't seem to make much difference.

I never thought about a 12V power adapter specifically for the machine. I don't know why I hadn't because it is an obvious solution. Found one on Amazon and have already ordered it.

The battery I got for free is a NAPA commercial type 31. I don't remember the exact model #, but I am going to see if it will run for two nights at the track this weekend. I have another battery I am going to take with me this weekend just as a backup

You're in Georgia, so I totally get why humidification isn't helping you. I don't use the humidifier in the summer either, but it's a necessity during the heating season for me.

Ok, with a group 31 battery (that would weigh around 75lbs), 12V adapter and an S9 without humidification, you may get a week of sleeping between charges if it's a deep cycle battery (and even a starter battery will get you more than a single night). Perhaps more, depending on the battery.

Let us know how the adapter works out for you. I've been meaning to pick one up for years as an emergency backup.

 

[Lucid Moments]

I am going to have to run it off the inverter again this weekend because the adapter won't be here in time. I will take the battery charger too just in case.

 

[Ralf11]

Considering how many people use CPAPS and how many people camp out, etc.

you'd think they'd make a CPAP that runs directly off of 12 V DC

 

[rlitman]

Considering how many people use CPAPS and how many people camp out, etc.

you'd think they'd make a CPAP that runs directly off of 12 V DC

They exist, but most people get their machine through insurance, and insurance will not cover a second machine. Plus you probably don't want one of these mini machines for everyday use.

 

[Sevenhills1952]

I guess I'm just weird or stupid (or both[emoji38]), but I've never understood CPAP machines. I understand how they work and purpose, but I know I couldn't sleep wearing one.
My wife & I, both late 60s, snore and our doctor says we both should have one (although grandparents both sides lived into 90s without one).
We use nose spray before bed, sleep all night no problems. It seems like something along the lines of walk-in tubs, back and knee braces or a stair lift.
Are these all improvements to life or money making gimmicks?
It's like these new truck tailgate lifts. When I'm so decrepit I can't step on the tire hopping into the truck bed it's time to quit driving! [emoji2]

Sent from my SM-S205DL using Tapatalk

 

[Ralf11]

they are improvements to life and prevent many, many deaths - sleep apnea is known to be implicated in large numbers of industrial accidents, much less car and truck crashes

 

[Lucid Moments]

Untreated sleep apnea is also related to heart disease in some way I don't understand, but I take my doctors word on it. I have a friend that had a heat attack in his mid 40's that his doctor blames largely on his untreated sleep apnea.

 

[jeepxj]

Untreated sleep apnea is also related to heart disease in some way I don't understand, but I take my doctors word on it. I have a friend that had a heat attack in his mid 40's that his doctor blames largely on his untreated sleep apnea.

thats what my afib is linked to per the doc.

 

[Sumboodie]

What kind of track does NASA have?

You talking about for jogging? dogs?

 

[Lucid Moments]

What kind of track does NASA have?

You talking about for jogging? dogs?

National Auto Sports Association. Road racing cars

 

[Lucid Moments]

You're in Georgia, so I totally get why humidification isn't helping you. I don't use the humidifier in the summer either, but it's a necessity during the heating season for me.

Ok, with a group 31 battery (that would weigh around 75lbs), 12V adapter and an S9 without humidification, you may get a week of sleeping between charges if it's a deep cycle battery (and even a starter battery will get you more than a single night). Perhaps more, depending on the battery.

Let us know how the adapter works out for you. I've been meaning to pick one up for years as an emergency backup.

Just as a follow up the 12v adaptor works like a charm. I haven't been to the track yet with it, but used it in my bedroom one night just as a test. It even comes with a 12v power adapter (cigarette lighter type) with battery clamps on it. So all you really need is this adapter and a car battery and you are ready to go. I bought a panel for an RV that has a power port, 2 USB ports, a voltmeter, and a switched power supply. Going to mount it on the wall of my trailer and hook up an LED light to the switch. Should make staying in the trailer nice and easy.

 

[rlitman]

Thanks! Looking at the charts from ResMed again, it seems that an AirSense 10 AutoSet uses almost twice as much current as an S9 AutoSet, with everything else the same (SlimLine tube and no humidifcation, in order to save as much on the battery budget as possible). Well, that seals the deal for me. Since I have both, I'll buy the 12VDC dapater for the S9 too. Not sure when I'll use it, but better to have and not need, than to need and not have.