Cpap Power For Boondocking

Discussion in 'Custom Additions' started by SethB, Apr 12, 2018.

  1. SethB

    SethB Novice

    I’m considering what electrical capacity / charging upgrades may be best for extended boondocking away from shore power. Ultimately, for me, a camper is a way to carry a big power source for CPAP usage. Otherwise, I couldn’t camp. Running out of power means going home or to another shore power source for sleeping or charging.

    My experience with a previous camper set up with LED bulbs and propane refrigerator is about 2.5 to 3.5 nights of CPAP use (no humidifier) on a Group 24 deep-cycle conventional lead-acid battery.

    It’s a project that will take weeks, if not months. I plan to document it in this thread, and, of course, welcome comments about power for extended boondocking, especially experiences of using CPAP off-grid.

    See also
    CPAP and battery.... (general needs and experiences with CPAP) (12v-12v chargers) (2nd battery, LED bulbs) (LED bulbs)
    Auxiliary Battery For Refrigerator (2nd “pony” battery in the TV)

    Charging: I live and mostly camp in shaded areas of the PNW, impacting the value of solar charging.
    Capacity: The battery compartment of the CI has been designed to accomodate a Group 24 battery, of about 78AH capacity. Period. There isn’t a straightforward way to up the power capacity in the trailer.
    Charging: The charging system of most TVs is not designed to optimally charge and top off a deep-cycle battery to full capacity.
    Consumption: It’s not straightforward to figure out power draws of CPAP and other power consumers. Nor, the time it takes to charge with alternator, solar, generator, etc. But, it is possible to get close with some figuring and testing.

    Consumption: Skip the 12v refrigerator. Buy a modern cooler like Yeti. (Done)
    Consumption: Replace the halogen light bulbs with LED. (On order, will report back on how they work)
    Charging: Add a 12v-12v charger, like the CTEK D250 or D250SA so that the TV does optimally charge and top-off the house battery.
    Capacity: Add CPAP-specific or other small Li-Ion battery systems. (Relatively expensive and single-purpose)
    Charging: Add solar charging. (Change camping style to embrace the sun? Out of character...)
    Charging: Add a 1KW or 2KW generator. Possibly convert to propane, supplied from the CI outlet. (Quiet gennies are expensive, but this is potentially unlimited and all-weather charging. Useful for other needs?)
    Capacity: Repurpose limited storage space to a bigger house battery, or, a second house battery.
    Capacity: Add a 2nd battery in the TV. Sometimes called a pony battery.
    Monitoring: Add a Trimetric or other device to really measure power in and power out. A voltmeter is not enough. This sort of monitor tracks capacity by percentage.
    Charging: Spend more camping time in sites that supply shore power. In this neighborhod that’s State and many County campgrounds.

    Cooler, not refrigerator.
    LED bulbs.
    Try (again) to figure out real CPAP power consumption numbers (“typical” manufacturer’s numbers aren’t enough!)
    List all the desirable destinations with shore power. List those without.
    Figure out off-grid charging. This is the big one.
    It’s probably time to replace the CI battery (2012). With stock size/capacity, or with something bigger?

    If it isn’t clear from the detail above, I’ve been researching this quite a bit, over a period of years (previous camper), and want to do this right!
    Tour 931 likes this.
  2. rotus8

    rotus8 Junior Ranger Donating Member

    I think you have covered all the basics, good luck and keep us up to date on your progress. One thought - is your CPAP a native 12 volt model? Using an AC machine with an inverter is significantly less efficient than a DC one designed to be run directly on 12 volts.
  3. Dean Pinter

    Dean Pinter Newbie

    Have you though of a separate unit like a Goal Zero? We have the Yeti 400 and a pair of Boulder 30 solar panels and use when we are off the grid. We basically use to power camp lights and charge things like phone and iPads. It really doesn't take up a lot of room but as you get to bigger models, they go up in size and weight. The nice thing about it is the display monitors draw and time left on the battery. This might be a good feature when using a cpap. If you know someone with one of these, you could at least plug in your machine and find out the actual draw. Hope this helps.
  4. SethB

    SethB Novice

    Quite right, Rotus8. I’m on a 12v-native CPAP, and have slept many nights on battery power (previous camper).

    For other readers, if I’m going to ditch the fridge and install LEDs, paying a penalty to convert 12v to 110v AC with an inverter, then have the CPAP’s AC supply convert it back to 12v is crazy!

    High quality sine wave inverters are rated at 90-95% efficiency. Lower quality modified sine wave inverters are less efficient - 75-85%.

    Where does the power go? Usually, to generating heat. Also, there would be some smaller loss in the CPAP’s AC power supply. 4 or 5%?

    Two more power consumers:
    Water pump
  5. SethB

    SethB Novice

    Re: Goal Zero, and other such approaches of smaller batts.

    That’s kind of unique, that it has built-in charging. But, at $599 list for a 400, that’s an expensive thing to leave in the sun, away from the shaded campsite. One could adapt, I suppose.

    A 400 has around half the capacity (40Ah) of the CI batt - $599. (16 lbs., sealed)
    A 1000 has around 96Ah capacity - that’s significant to the CPAP user! But at $1300 it’s an expensive solution. (40 lbs.)

    Oops, those prices *don’t* include solar charging.

    To put that in perspective, a heavy Trojan SCS225 deep-cycle runs about $200, plus or minus, for 130Ah. (60 lbs., wet lead-acid)

    If you were camping sunny, though, a Goal Zero 400 with solar could run indefinitely. I think you might need the big Boulder 200 panel though, for another $575.

    I guess all that needs closer figuring on the panel size. But, li-ion batts are certainly much more expensive than lead-acid for a given capacity.
  6. AlCat

    AlCat Junior Ranger Donating Member

    I went with dedicated small batteries for my CPAP (no humidifier). Each battery gives a full night's CPAP use. (1+ days, actually, though not sure how much the "=" is.) No doubt this is an expensive approach (though it should be cheaper today than when I bought my batteries a few years ago). And it only gives me two nights (two batteries)

    I do have a solar panel (Zamp refurb'd), but as you noted, that doesn't help in forested campsites.

    Seems that the only solution is a (gasoline) generator.

    Am sure that getting rid of the fridge helps, a lot. My wife isn't willing to do that (even though we have TWO Yetis). She likes the convenience of the fridge. I'm not sure she's evaluated how inconvenient it will be if I die of a heart attack a few miles from a paved road.....

    Your post makes me wonder if I should look at newer (more efficient?) models, or perhaps a
    12V version....maybe I'd get an extra day out of each battery

    I did buy a snore guard designed to help with sleep apnea, but it doesn't help as much as we'd hope, unfortunately. For some folks, the snore guard is enough. Probably worth checking if your medical insurance covers another appointment with your sleep doc. They did have to conduct another sleep study, to see how the device worked in practice.

  7. Randy

    Randy Ranger Donating Member

  8. SethB

    SethB Novice

    That’s interesting. Li-ion is still expensive per amp-hour, but this seems more toward the “value” side of product design than, say, Goal Zero.

    Maybe. I have to say I’m confused by the specs on this page:
    Omni 20 Power bank with wireless charging and direct DC Input/Output
    Cell Dimension: 18650 Li-ion battery by Panasonic/LG chem/Samsung
    Capacity: 6 cells, 73Wh (20400mAh at 3.6V)

    The 18650 is a 3.6 or 3.7 volt battery. I guess that spec means 20Ah at 22v... um, no, that doesn’t work, that would mean 440 Wh. This means some figurin’, I guess.

    3 3.6v batts = ~12v (10.6v actually, but call it 12)
    At 3Ah (~3000MAh/batt, average for an 18650, but they’re in series)(M for milli, multiply/divide by 1000, 3 decimal places)
    Means about 6Ah for 6 batts in series/parallel. More or less.

    More figuring needed, their specs are a little confusing, but that may be down around 1-night of CPAP, or possibly less.

    I’ve not yet found my spreadsheet from the last time I tried to determine the draw of my CPAP, but, I know I’d be a lot more comfortable with another 100 Ah than 6 Ah. If I have that right...

    I’m suspecting there is no li-ion battery magic. A package of affordable li-ion designed for charging power-efficient cellphones, tablets, and laptops just may not be suited to the demands of a motor and air-pump in a CPAP. It just takes a lot more energy to spin a motor against a load for 8 hours.
  9. Randy

    Randy Ranger Donating Member

    That's some pretty good ciphering! I don't know too much about electricity, wish I knew how to calculate watt hours and the like. I got the Omnicharge to run my battery powered Rumpl Puffe heated blanket. The batteries that came with it only last 2-3 hours and the Omni can run it all night. It's pretty sophisticated in that you can set the exact output voltage. Seems like running a CPAP without shore power is a commonly asked question on many of the forums. You would think there would be a good solution by now. Best of luck, keep us posted!
  10. SethB

    SethB Novice

    I suppose that as I’ve gotten all these considerations written out, I’m already resigned to something big and bulky and awkward. Whether that’s a (sustantial) solar panel (probably not, for our camping), a generator, or a really big battery. Any way you slice it it takes bulk if not mass for higher capacity.

    Well, excepting a 12v-12v charging system for people who are driving every couple of days. Or staying on-grid. But that hasn’t been us for most of our camping.
  11. TimeCapsule

    TimeCapsule Newbie

  12. Handben

    Handben Junior Ranger Donating Member

    It'd be helpful to know how many watts your CPAP pulls in order to do the calculations as to what you need. You might consider purchasing a "killa-watt" energy monitor which will give you a pretty precise reading of the energy consumption:

    Be aware that if you're using lead based batteries that you really should not discharge more than 50% or you'll drastically reduce the life expectancy of the battery. The fact that lithium batteries don't die when discharged deeply (ex your laptop or phone) plus roughly 25% of the weight is a major selling point for lithium battery technology.

    For me it's easier to think about battery capacity for any given electrical draw using watt-hours rather than amp hours. If you know for instance that your CPAP draws 30 watts and your battery capacity is 400 watt hours then the length of time is 400watt hours/30 watts = 13.3 hours. I bought a "lithium solar generator" - kind of a gimmicky marketing strategy but that's what they all call them - which has a 400 watt hour capacity. It can be recharged with solar panels. It's probably not enough capacity though for your needs and I suspect that the hassle of trying to get it recharged every other day would get old quick.

    If you plan to be off grid for several days at a time, you could consider a larger lithium battery. A 100 Ah would give you 1200 watt hours of power and would weigh roughly 28 pounds. These are pretty $ though ~ $1300 for this size "smart battery".
  13. SethB

    SethB Novice

    Handben, your post got me thinking about several things.

    First, I think you’re right - watt/hours are helpful, especially in evaluating li-ion batteries. Ah x 12 (nominal for lead-acid) = Wh. Or, MAh x 3.7 (nominal li-ion, per cell) = Wh.

    I’ve not yet found my figures from the last time I got a new camper and was figuring battery life. But, I did browse over to - I highly recommend this site for CPAP users - and came across a great thread summarizing the issues and possible solutions. It wasn’t up the last time I was researching.

    I’ve not yet read and considered all of it. It could be that my CPAP (with humidifier off) only burns about 6 to 8 Ah, or, 72 to 96 W/H. An auxiliary / pony AGM (no gas venting!) of 100 Ah capacity, drawn down 50% (that’s it for long life of lead-acid batts), would cost about $165 and provide 6 to 8 nights use, without touching the CI batt or recharging.

    This batt:

    It’s AGM and therefore safe around living/driving areas, it weighs 60 lbs, and costs $165. Give it a good charge at home (more $ for a good charger, and a battery box), and I have 5+ nights easy, with the CI batt used only for lights, water pump, furnace, charging phones/tablets... so it has some unused capacity for backup as well.

    Where does this battery live? My current TV is a pickup. Possibly it lives in the covered bed when camping, and I figure a cable pass-through, install a 12v socket in the CI 550 cabinet (my 2012 is old enough that it doesn’t have one)... something like that.

    Of course 60 lbs. is chunk of mass, and other solutions would be lighter. Li-ion can be drawn all the way, I think, so the equivalent would be 50 Ah, or 600W/H for a 12v pack, about $500, weighs 12 lbs.
  14. AlCat

    AlCat Junior Ranger Donating Member

  15. AlCat

    AlCat Junior Ranger Donating Member

    I have a related question: what's the best way to recharge the cpap battery?

    If you do use a standalone battery for the CPAP (rather than the onboard battery), and you are recharging the TD's onboard battery via solar, is it problematic to charge the cpap battery IN the TD (via the 12V outlet) at the same time you are charging the onboard battery from solar? (I realize that the solar would be charging the onboard TD battery which would in turn be charging the cpap battery)

    I've tried recharging the CPAP battery via the TV's battery (if we take the TV for a day trip away from the TD), but that probably isn't charging the cpap battery much and it may be stressing the electrical system of the TV.
  16. SethB

    SethB Novice

    Indeed, that cabinet for a CPAP is one of the reasons we first looked at CI. There’s only one other small teardrop I’m aware of that has shelves or cabinets at the head of the bed, though almost any builder willing to do custom work would put in a shelf.

    For some reason I’d not thought about that as a battery space, too. You’re right though. That would probably mean *not* getting single 100Ah battery, because it’s a bit too big and who wants to lift 60 lbs. into the cabinet? That argues for a max U1 size battery at 20 or 24 lbs. But get two of them. I’ll be thinking about that!
    Essentially, you’d be running two batteries of different capacity in parallel during the charging phase. I’ve read people discussing the merits of batts in parallel - almost all say that the batts must be matched for type and age, because, as soon as you connect in parallel the more deeply discharged will quickly draw down the other battery. That’s regardless of the solar input, and could happen quickly enough to get a batt well into the danger zone, which is bad for longevity.

    There are battery switches for marine use though - the idea is that with various configs of a switch or two you can decide which battery is charging, which battery is under load, etc. It’s true you have to keep track to meet your goals, but it’s safer than wiring it all together!

    Or, instead of marine battery switches, read about using an isolator instead:
    Auxiliary Battery For Refrigerator
    ***end Edit***

    Depending, it could bring the CPAP battery up considerably. But that’s coming from the TV alternator, not the TV battery, when it’s running. When it’s not running you should disconnect the CPAP and TV batteries, because then, you’re back into charging one battery from the other, in parallel, and might draw down the TV battery real fast. That’s even worse for a car battery (starting) than it is for a deep-cycle (trailer) battery.

    Because such draws really depend on the state of charge, they *can* be done under some circumstances. But most people play it safe, since making a mistake has such a big impact on longevity of a battery, an/or, your ability to start the car in the morning!
    Last edited: Apr 17, 2018
  17. TimeCapsule

    TimeCapsule Newbie

    I guess if you are feeling adventurous - you could look at the Chinese sites like Aliexpress for lithium batteries. There is quite the selection, but it is a leap of faith on the actual quality and performance. Here is a 12V, 60aH battery for $190:
    Ultra large capacity 12V 60AH,80AH,100AH,120AH,150AH,180,200AH Lithium polymer LiPo Chargeable Batteries for devices power bank -in Replacement Batteries from Consumer Electronics on | Alibaba Group

    I was thinking of getting a LiFePO4 battery for the trailer, but the prices are pretty high still. I think they may come down with time.

    This one looks interesting for $240:
    12V lithium ion solar motorcycle jump starter 60AH lithium ion battery Multi function -in Electric Bicycle Battery from Sports & Entertainment on | Alibaba Group
    Last edited: Apr 17, 2018
  18. AlCat

    AlCat Junior Ranger Donating Member

    Not having a CPAP after two days is also bad for longevity!! MINE!

  19. SethB

    SethB Novice

    Quite right, and note to TimeCapsule: "Adventurous" would *not* describe any user of CPAP who is actually receiving the benefits of therapy. It's 10 or 12 years for me at this point, and stability and reliability of the therapy is incredibly important to my happiness, relationships, and productivity every day.
    I think it's difficult for non-CPAP users to truly understand the positive impacts this therapy have had on our lives, and, as AlCat wrote, to the duration of our lives.

    That's why a primary power system (1 or 2 dedicated batts capable of multiple nights) and a backup (the house batt, capable of at least a night or two when needed) sounds so good. Stability, resilience, and backup means peace of mind!
  20. Randy

    Randy Ranger Donating Member

    There is a great thread on how to install an auxiliary batter in you TV with an isolator. Has worked out great. I now keep my domestic in the back of my truck hooked up to the auxiliary battery and it has effectively doubled my battery capacity.
    AlCat likes this.

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