Forum Discussion

Bordercollie's avatar
Bordercollie
Explorer
Sep 03, 2023

Battery Power for My CPAP

There are a number of solutions for short term powering of CPAP machines while off-grid camping or during power outages, with quite a range of costs. I use a ResMed Airsense 10 CPAP with humidifier and heated hose features disabled. I use a ResMed 12vdc to 24vdc converter,($100) connected to two (2) 12volt 18 amp hour sealed lead acid batteries,($100 per pair) connected in parallel, for 12 volts 36amp hour capacity. I get three 8-hour nights CPAP operation and end voltage is 12.53 volts. I might get a fourth night's worth but don't want risk stressing batteries and shortening their useful life. I use a 12 volt "Battery Minder" smart trickle charger ($50) to charge and maintain the batteries. I takes some 24 hours to recharge the batteries and charger switches to maintenance mode, I leave the charger connected continuously. I use two of these same SLA batteries in my mobility scooter. Note, my CPAP will run on any 24 volt DC source. The 110 volt AC power supply, for home use, provides 24 volts DC to the CPAP. I could also connect the DC to DC converter to my RV's house battery to power the CPAP while off grid but prefer to save house batteries for lights, furnace fans, and appliance controls, etc.
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  • Bordercollie's avatar
    Bordercollie
    Explorer
    Sep 06, 2023
    Grit Dog, Converting RV house batteries to Lithium is not cheap or simple, you will need to change the converter charger to a lithium type. Lithium batteries need to be protected from low temperatures. It's doable.

    Rick Jay, I'll try series connection for 24 volts without using converter. I will need a 24 volt charger or can charge each 12 volt battery separately with 12 volt charger.

    Connecting two batteries in series and getting the same capacity/duration just doesn't seem right. BTW, my moniker on RC Groups forum is "E-Challenged" for good reason.
  • Grit_dog's avatar
    Grit_dog
    Navigator
    Sep 06, 2023
    Seems like having ample amp hr capacity is the goal.
    Why not upgraded your house battery setup (cheaper amp hr/$) a bit.
    If you’re gonna spend $200-400 why not get 200-400ah? Seems like you could wire that up in a jiffy with your knowledge.
  • Rick_Jay's avatar
    Rick_Jay
    Explorer II
    Sep 06, 2023
    Bordercollie wrote:
    I know I could connect the same two batteries in series, and eliminate using the converter, but the capacity would be 18 ah.


    That is correct, the AH capacity would be 18AH. BUT...the current draw from a 24V source would be 1/2 of what the converter has to draw from a 12V source, so the net effect on how long the batteries would last would be the same. (The power going into the converter (I*V = I * 12V) has to be equal (technically, a bit greater, but we'll simpify here) to the power going into the CPAP (I * 24V).) Anyway, battery longevity should be the same, and possibly a smidgen greater, without the converter in play.

    Good Luck as you search for options. :)

    ~Rick
  • Bordercollie's avatar
    Bordercollie
    Explorer
    Sep 05, 2023
    I am someone who is into RC models and use lipoly batteries in series and parallel for different applications. I connected two 12 volt 18ah SLA batteries in parallel to double the capacity (36 ah) because I had them. I know I could connect the same two batteries in series, and eliminate using the converter, but the capacity would be 18 ah. I imagine I might get one or possibly two nights CPAP use. I may try two 12 volt 2Oah LIfe POR batteries, now relatively cheap, in parallel with converter or in series without converter and test for actual results. Will have to buy a Lithium charger though. I may convert to Lithium batteries for my mobility scooter also.
  • theoldwizard1's avatar
    theoldwizard1
    Explorer II
    Sep 05, 2023
    Find some one who is into remote control (RC) models (cars, boats or airplanes). They can make you up a lithium 24V battery pack (or wire 2 12V packs together) For probably less than $100. You will have to buy a special charger for that. Much less than $200 with the charger and it will last for years !
  • Rick_Jay's avatar
    Rick_Jay
    Explorer II
    Sep 04, 2023
    Bordercollie wrote:
    I use a ResMed Airsense 10 CPAP with humidifier and heated hose features disabled. I use a ResMed 12vdc to 24vdc converter,($100) connected to two (2) 12volt 18 amp hour sealed lead acid batteries,($100 per pair) connected in parallel, for 12 volts 36amp hour capacity.


    Hi Bordercollie

    I'm wondering why you put the two 12V batteries in parallel when your CPAP needs 24V? If you put them in series, you'd be at 24V with an 18 AH capacity. Power wise, it's the same. That 12V to 24V converter uses up a bit of power in the step up conversion process. Maybe not much, I didn't research the technical data for the unit, but it does use some power.

    Since that converter costs what a pair of batteries cost, for the same initial investment, you could have an extra set of batteries. This way one pair of batteries could be charging and standing by while the other pair was being used. This would provide you at least 6 days, maybe 7, of battery use. Of course, since you already have the 12V-24V converter, it's a moot point. But if it should start acting up, this might be something to consider, if you haven't already.

    Anyway, I know nothing about CPAPs and such, and I guess the 12V to 24V converter is something you'd use for other purposes anyway. I was just wondering if this was something you investigated along the way.

    Take care,

    ~Rick
  • Bordercollie's avatar
    Bordercollie
    Explorer
    Sep 03, 2023
    There are 18 ah rated lithium batteries that weigh around 1/2 as much as sealed lead acid ones, but they require special lithium chargers and cost more than SLA's. There are also some small lightweight lithium CPAP batteries that cost nearly $400 and only give one night's CPAP power. There are solar power setups that can charge CPAP batteries for unlimited CPAP power. Many choices.
  • pnichols's avatar
    pnichols
    Explorer II
    Sep 03, 2023
    FWIW regarding powering CPAP machines when camping without hookups:

    The lowest power way to run them is to purchase the little converter bricks for each one that plug into an RV coach's 12V receptacles and raise the voltage to around the 24 volts DC that the common CPAP machines require (ours are Resmed AirSense models 10 and 11). These little DC-to-DC converters are available on Amazon and don't cost much. Note that these converters must actually state which CPAP models their output connector will plug into because for instance - the Resmed 10 has a different input receptacle type than that of the Resmed 11.

    Using these DC-to-DC converters causes less drain on RV battery systems than using inverters to run the CPAP machines via 120V AC ... because 12V DC to 120V AC inverters waste energy in their conversion process.
  • NamMedevac_70's avatar
    NamMedevac_70
    Explorer II
    Sep 03, 2023
    I also use the fantastic ResMed AirSense CPAP for 7 years now and without the water or heated hose with no problems'. When on camping and fishing trips I leave at home as my OSA is mild. I will copy and save your very useful info for the future and thanks for that.

    Cheers to the soggy, muddy BM and the Ps.

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