CPAP at Pennsic (v2.16)
By Master Phillip the Pilgrim, O.P.
What follows is a quick-and-dirty discussion of what it takes to use a CPAP or other medical electric equipment at Pennsic or other camping event, based on my 11 years of living with a CPAP machine and 20 years as a ham radio operator.
You need a minimum of three things to run your CPAP at Pennsic:
2) Battery Charger
3) Power cables to get battery power to your machine
Due to the way lead-acid batteries work internally, you'll want a 12 volt deep cycle battery, also sometimes called a marine battery. You can get these at nearly any auto parts store. You could use a regular car battery in a pinch. However, you will ruin a car battery in short order (20-40 use/charge cycles). That's because car batteries are designed to provide short bursts of extremely high current, which is what the car's starter needs. Deep-cycle batteries are designed for long, slow, low-current applications, which is a perfect fit for powering smaller devices such as your CPAP. (Note: while we call them “12 volt batteries,” lead-acid battery chemistry actually gives closer to 12.8 volts at full charge.)
Battery capacities are measured in amp-hours. This is, as you might expect, the number of amps your device draws multiplied by the hours you run it. Equipment running on a 12 volt battery that draws 3 amps for 8 hours would use 24 amp-hours (3x8). My CPAP draws 1.5 amps in short peaks, but it averages under half that. I find I use about 5 to 6 amp-hours per night (measured with a special meter). Other equipment will have different power requirements; use the equipment's label as a starting point.
You should plan on a battery that has a capacity of at least 3 times the amount you're going to use overnight. More would be better. Repeatedly drawing the full charge out of a battery wears it out faster. I currently use a 50 amp-hour battery, recharging it every other day at Pennsic. My previous battery was 80 amp-hours, and I could get along with a recharge once every four days.
Typical marine batteries still have the caps where you put in water. That means you should be checking the water level every few days and topping off with distilled water if the tops of the plates are out of the water. You can also get sealed lead-acid (SLA) batteries, though you might have to go to a specialty battery store.
Sealed batteries need a slightly different charging plan. There's also another kind of sealed battery called Absorbed Glass Mat (AGM), named for the construction of some of the internal components. AGM batteries can take more electrical abuse than most others, but they cost 2-3 times as much.
This is the battery I currently use:
My previous battery was a marine Diehard battery from Sears.
There are lots of battery chargers out there. The better ones analyze the battery while charging, to keep from overcharging. This is the charger I currently use:
If you're using an SLA battery, you should run the charger on the lowest setting. In the case of the Black and Decker charger listed here, charge at the 2 amp setting. If you get an AGM battery, look for a charger that has an AGM mode.
Most CPAP 12 volt power cables plug into the CPAP on one end and have something that plugs into a cigarette lighter socket on the other end. The particular cable will vary with the brand of CPAP machine you have. You should be able to obtain the appropriate cable from your CPAP supplier, or here:
I've dealt with CPAP.COM in the past. They are quick and reliable.
You'll need something that has a cigarette lighter socket on one end and clamps that attach to your battery on the other end. They look like this.
Radio Shack carries a similar item. You can also find battery cases that have built-in cigarette adaptors and handles. These are typically found at sporting goods stores near the fishing equipment.
Nice To Have
will find it useful to monitor the charge of your battery, to see how much
capacity you’ve used. Fortunately with lead-acid batteries, the capacity
remaining is directly related to the voltage when the battery is not under load
(not powering anything). An inexpensive volt meter will quickly tell you how
close you are to needing a recharge. Fully-capable voltmeters can be found for
under $20 – I’ve seen them at Harbor Freight and on Amazon for $10 or less.
This one works really
A fully charged battery with no load will read somewhere in the 12.8v range or higher. A lead-acid battery is completely discharged when the meter reads 12.0 volts. Pulling more energy out of a fully-discharged battery will cause internal damage, eventually destroying the battery’s ability to hold a charge. Plan on recharging when you hit 12.2 volts.
Any "true sine-wave" inverter will work well, but those are even more expensive.
•At Pennsic, CPAPs fall into the area covered by Disability Services. You need to check in with them to get a time slot at a charging station.
• If you intend to use the battery for other purposes besides your medical equipment, such as charging consumer electronics, be sure to account for the extra amp-hours when you size your battery. You can charge a cellphone without much impact. If you want to power your laptop however, that will draw a lot more, which means you'll need a bigger battery.
• And remember: you can use the battery at home to power your CPAP in case of a power outage. It's a good idea to use your battery once or twice a year at home, just for maintenance purposes. After you use it, charge it before you store it.
• The air at Pennsic is notoriously smoky, especially at night. Your CPAP will be taking that smoke-laden air and pumping it straight into your lungs. If your CPAP is capable of using a disposable high-efficiency particulate filter, you should use it. At Pennsic, I replace my filter every two to three days. It starts out snow white, and it's almost black when I pull it out. That black stuff is something that would have gone into my lungs if the filter wasn't there.
• You'll want to have some way to transport your battery to the charging station. Batteries of this capacity weigh 40 pounds or more. Little red wagons are good, as well as useful around camp and for ice runs.
I'm often asked if there is an alternative to taking your battery to a charging station. Perhaps an alternative power source, such as wind or solar, would work?
The answer is indeed yes. However, there are some issues that make alternative power less attractive than it might seem at first blush.
To begin with, you have to generate at least as much energy during the day as you use at night. In fact, you'll need to generate more, since charging a battery is not 100% efficient. You need to put more amp-hours into the battery than you took out. If you used 10 amp-hours overnight, you'll probably need 14 amp-hours to get your battery back to where you started. So in order to determine if alternative energy sources make sense, you will need to know how much energy you use in a typical day. In my own case, I found that my CPAP machine uses about 5 amp-hours a night. (I have a specialized meter that measures amp-hours.) Your situation will be different, and your exact numbers can be hard to determine. You can make a rough estimate by looking at the sticker on your equipment, then calculate current draw in amps X expected run time in hours X 1.4. Keep this number in mind as you look at options.
Also remember that you could always get days where the sun doesn't shine much, or the wind doesn't blow much. So, you'll need spare capacity to get through those days, or a regular charger to use as a backup.
You've probably seen little solar panels that you put on your car's dashboard and plug into the cigarette lighter. These are used to keep your car battery topped off if you're not going to start it for a while, and they work well for that purpose. However, if we are lucky they put out a whopping 0.1 amps in high sun. To produce 10 amp-hours, you'd need to use the panel for 100 hours. Not nearly good enough.
In May 2102, I purchased a solar panel that can produce 1 amp in full sun. It’s about 15x20 inches and cost $75. It needs a charge controller, so add another $25 or so. For $100, I expect to be able to produce 5 to 7 amp-hours per day if I’m lucky. Since my CPAP uses about 5 amp-hours overnight, I need about 7 amp-hours per day to keep the battery charged. The math suggests that I should be able to just barely stay caught up using solar alone (as long as the weather cooperates).
Next up would be the solar panels that you can use to charge laptops. The best on one the market I can find right now is from California Solar Accessories. Their 40 watt folding kit can easily charge an 8-10 amp-hour battery in a day of good sun. That's better, but the cost is getting up there ($350+).
If you need more and still need to be even remotely portable, we have to look at RV/marine power solutions. There are quite a number of options here, but they all have a couple of common issues: size and cost. You can produce a considerable amount of energy with panels that start about 10 square feet and up - that's a 3 ft. x 3 ft. or larger panel that you'd have to transport and accommodate somehow in your camp. It needs to be mounted so you can aim it at the sun, plus it needs a clear view of the southern sky. And, we all know what they look like. Costs of these solutions run in the $500-$1000 range which includes all the required accessories (like a charge controller) but doesn't include a battery or mounting system.
You can feel free to contact me if you have questions or ideas. I can be reached at:
phil [at] moyen.org
preed [at] dnaco.net
I'm also on Skype, but email first.
This article was created for informational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding your medical equipment. Never disregard professional medical advice or delay in seeking it because of something you have read here.