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  • Camping CPAP System

    I am wanting to put together a system that will be primarily used for camping, but will also be a backup system at home in the event of power outages. I am considering solar for the ability to go beyond a set number of days of use. However, determining how much panel I would need has become an exercise in discovering my limitations in science and math. Hoping for some assistance.

    I do not have the manual for the CPAP, but here is the power info from the bottom of the machine: 100-240V ~ 50/60Hz 12 V (A long line with 3 beneath it). AC 1.0 A Max. DC 3.0 A Max.

    I am looking at using 2 18AH SLA batteries for size and cost if acceptable in this application. Batteries

    It will be run approximately 8 hours per night. The only thing being run on this is the CPAP machine. No humidifier, lights, charging phones, etc., purely a CPAP power system.

    I have considered a massive marine deep cycle battery and an inverter, but I would like something smaller, lighter, and usable in all situations if it makes sense to do it that way. I do have the DC setup and have used it off a small jump box in the past, but I could only get a night and a half out of that. If I understand the basics of amp hours correctly, using an inverter uses less power?

    Thanks for any help.

  • #2
    120v at 1 amp for 8 hours works out to 960 watthours. You're going to need a 400AH battery at 12VDC to handle that.

    WWW

    Comment


    • #3
      Get a generator. It will take a 400 AH 12 volt battery or about 300 pound battery costing you $900 to $1000 every few years replacing it. Not exactly camper or wallet friendly. You wan tsolar to go with that, another $1000 for 500 watt panels.
      MSEE, PE

      Comment


      • #4
        Can it run on 12v?

        Comment


        • #5
          Mike here ( a fellow hosehead )

          You will have to turn off the humidifier for your CPAP to run off a battery that you can lift.

          I run mine (10" H2O) off of a 12V auto jump start pack.

          This thread
          http://www.solarpaneltalk.com/showth...highlight=cpap
          covers another users CPAP quest. The last message there (29) covers my working pack.

          Mike

          update - CPAP stickie http://www.solarpaneltalk.com/showth...-camping-power
          Last edited by Mike90250; 10-16-2014, 09:43 PM. Reason: added 2nd link
          Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
          || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
          || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

          solar: http://tinyurl.com/LMR-Solar
          gen: http://tinyurl.com/LMR-Lister

          Comment


          • #6
            I have to say I don't understand the math behind this. I know a guy who uses the same 2 batteries I linked to, with a 175 watt inverter because his CPAP doesn't do DC, and gets 4 or 5 nights out of it for his CPAP he just can't figure out the solar charging aspect of it. How is it one CPAP is going to need a battery that weights 300+ pounds just because I want to charge it with solar panels? I don't mean that snotty, I truly don't understand it.

            Comment


            • #7
              Originally posted by Mike90250 View Post
              Mike here ( a fellow hosehead )

              You will have to turn off the humidifier for your CPAP to run off a battery that you can lift.

              I run mine (10" H2O) off of a 12V auto jump start pack.

              This thread
              http://www.solarpaneltalk.com/showth...highlight=cpap
              covers another users CPAP quest. The last message there (29) covers my working pack.

              Mike

              update - CPAP stickie http://www.solarpaneltalk.com/showth...-camping-power
              I used to use a Black and Decker jump box with a 17ah battery but it's dead now. I was just looking at something that would give me more than a couple days without it being a group 27 marine battery, or two. I just can't grasp why it is that adding solar to it changes it to something so massive.

              Comment


              • #8
                Originally posted by CampingNut View Post
                I do not have the manual for the CPAP, but here is the power info from the bottom of the machine: 100-240V ~ 50/60Hz 12 V (A long line with 3 beneath it). AC 1.0 A Max. DC 3.0 A Max.
                Lets help you with the math.

                Power = Watts = Voltage x Current. At 1 amp AC we know the voltage to be 120 volts. So 120 volts x 1 amp = 120 watts. Power is the rate at which work is being done and is a static measurement at a moment in time.

                Electrical Energy = Watt Hours = Watts x Hours.. You want 8 hours so 120 watts x 8 hours = 960 watt hours.

                Battery stored energy is measured two ways. You know Amp Hours. Like watt hours the Amp Hours = Amps x Hours. It can also be measured in Watt Hours which is what we need to know to supply energy for something. Batter Watt Hours = Battery Voltage x Amp Hours.

                There is the math, now put it to work. We know or think you want 960 watt hours per day. For batteries, at least for flooded lead acid (FLA) to maximize battery life, and cover your but for 2 cloudy days you limit daily discharge to 20% of the capacity or 5 day reserve. You can go as low as 50% or just a 1 day battery, cloudy day you are screwed. So 5 days x 960 watt hours = 4800 Watt Hours or 4.8 Kwh. To find the amount of Amp Hours needed you need to know the operating voltage and we know it is 12 volts right? AH = Watt Hours / Battery voltage. 4800 wh / 12 volts = 400 AH @ 12 volts. FLA batteries weigh roughly 60-lbs/Kwh. Well you have 4.8 Kwh battery then it must weigh 60-lbs x 4.2 = 252 pounds. How much does a good battery cost. $180 to $220 Kwh. or $180 x 4.2 Kwh = $756 to $924. Cheap 1 year batteries $80/Kwh

                Now go figure out what you can do with your batteries.
                MSEE, PE

                Comment


                • #9
                  Originally posted by Mike90250 View Post

                  try reading this.
                  Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                  || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                  || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                  solar: http://tinyurl.com/LMR-Solar
                  gen: http://tinyurl.com/LMR-Lister

                  Comment


                  • #10
                    my advice to play it safe is get a 240 watt panel and a mppt controller to get its full output. You can get several small batteries 18 amp, or even 28 amp or bigger, the large panel will charge them quickly the next day, so you can use them at night. You just need to charge each battery seperately unless they are the same brand/same amperage then you can parallel them. During the day your equipment connected to the battery being charged/floated by solar panel, is actually running off the panel. Thats how my system is setup, the 145 ah battery I have is usually floating by 11 am, all my stuff is running off the battery, as load is put on the battery the float amperage from the solar panel goes up. i have a led voltmeter/ampmeter connected from the charge controller to the battery, so I see everything in realtime.

                    Solar is very simple and you dont need multiple panels or large batteries. If the weather is always bad then you might need a big battery to get you through the cloudy days. By big I'm talking 100 amp hour which can weigh in the 70 lb range.

                    I recommend the 240 watt panel because thats what I have and even in cloudy weather I get usable power out of it. Even in cloudy weather it should charge up an 18 amp battery. I dont worry too much about the formulas or cost versus grid. All I know with 240 watts in sunny conditions I can get up 12 amps of charging power which will easily charge up an 18 amp battery, some people here say its overkill but you can never have too much amps. You just have to make sure your battery can handle the high amp charge rate. A 240 watt panel is large but it will easily fit on the roof of a van or RV. By comparison a 120 watt panel (which I also had) puts out about 6 amps, in cloudy weather your lucky to get more than 1 amp out of it, that why I wouldnt recommend it.

                    Comment


                    • #11
                      Originally posted by CampingNut View Post
                      I have to say I don't understand the math behind this. I know a guy who uses the same 2 batteries I linked to, with a 175 watt inverter because his CPAP doesn't do DC, and gets 4 or 5 nights out of it for his CPAP he just can't figure out the solar charging aspect of it. How is it one CPAP is going to need a battery that weights 300+ pounds just because I want to charge it with solar panels? I don't mean that snotty, I truly don't understand it.
                      We can only work with the numbers you gave us. And they were 120VAC at 1 amp max for 8 hours.

                      So unless you can get us more accurate numbers to work with that's all we can really give you. My advise is get a Kill-A-Watt meter and run it for a few nights to get more accurate numbers. It would also allow you to test things like how much it uses with/without the humidifier.

                      WWW

                      Comment


                      • #12
                        Originally posted by Wy_White_Wolf View Post
                        We can only work with the numbers you gave us. And they were 120VAC at 1 amp max for 8 hours.

                        So unless you can get us more accurate numbers to work with that's all we can really give you. My advise is get a Kill-A-Watt meter and run it for a few nights to get more accurate numbers. It would also allow you to test things like how much it uses with/without the humidifier.

                        WWW
                        I have used my kill a watt meter on my CPAP with and without the humidifier. I will have to find where I wrote down the watt hour usage and get back to this posting but I do remember even though the power supply was rated 120vac at 1 amp it did not use anywhere near that many watts. I believe the power supply is sized to handle the CPAP and the humidifier (uses a hot plate in a water reservoir) at it's highest setting.

                        From what I remember I can easily use my 65Ah Blue top battery without the battery ever getting below 20% DOD with the CPAP set at 9 psi and the humidifier at 1. But again that is from memory which is not as good as when I didn't use that darn CPAP.

                        Comment


                        • #13
                          Originally posted by jony101 View Post
                          my advice to play it safe is get a 240 watt panel and a mppt controller to get its full output. You can get several small batteries 18 amp, or even 28 amp or bigger,
                          You should not be giving any advice. Putting a 240 watt panel on a 12 volt 18 to 28 AH is a great recipe for a fire or explosion. Minimum size battery for a 240 watt panel with MPPT is 160 AH for FLA or 80 AH AGM.
                          MSEE, PE

                          Comment


                          • #14
                            Originally posted by jony101 View Post
                            my advice to play it safe is get a 240 watt panel
                            What is the basis of your recommendation - other than that you have such a set up which has no meaning.
                            [SIGPIC][/SIGPIC]

                            Comment


                            • #15
                              I couldn't find my old records for my CPAP machine so did some testing over the weekend.

                              With just the blower going at 10 psi it is using an average of 45watt hours in an 8 hour time frame. When the CPAP blower is not running but still powered it is using an average of 30watt hours during the remaining 16 hours of the day just sitting there. Talk about a Vampire load.

                              With the humidifier at level 1 it is using an average of 150watt hours in an 8 hour time frame.

                              So if I only "use" my machine for 8 hours it will consume about 4 AH at 12v a night without the humidifier and close to 13AH in a night with the humidifier at level 1.

                              With only using the CPAP blower and unplugging it when not in use I believe mine can be run on a 20Ah battery if I charge it every day and easily a 50Ah battery charging it every other day.

                              Of course a different CPAP machine may use more or maybe less power than mine.

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