CPAP-a-Pensic-art - 7/13/11
"CPAP at Pennsic" by Master Philip the Pilgrim.
This article was submitted to me by the author for inclusion in this set of files, called Stefan's Florilegium.
These files are available on the Internet at: http://www.florilegium.org
Copyright to the contents of this file remains with the author or translator.
While the author will likely give permission for this work to be reprinted in SCA type publications, please check with the author first or check for any permissions granted at the end of this file.
Mark S. Harris...AKA:..Stefan li Rous
stefan at florilegium.org
CPAP at Pennsic (v1.13)
By Master Phillip the Pilgrim
What follows is a quick-and-dirty discussion of what it takes to use a CPAP or other piece of medical electric equipment at Pennsic or any other camping event, learned from my 10 years of living with a CPAP machine.
You need three things to run your CPAP at Pennsic:
2) Battery Charger
3) Power cables to get battery power to your CPAP
Due to the way 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 (20-50 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.
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. A CPAP running on a 12 volt battery that draws 3 amps for 8 hours would use 24 amp-hours (3x8). My current CPAP draws 2 amps in short peaks, but it averages less than half that. I find I use around 5 amp-hours per night on my 2009-era CPAP. (My older machine, from 2001, used 12 to 14 amp-hours per night with 3 amp peaks.) 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. 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 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.
More exotic battery types, such as lithium-polymer (think: cell phone or hybrid car) are not yet available in the capacities we need at prices we can afford.
There are lots of battery chargers out there. The better ones analyze the battery while charging it, 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 - tell them you need to run your CPAP in an RV. You can also shop 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.
Another power option is something called an "inverter". This hooks to a 12 volt battery and puts out something resembling household AC wall power on the other end. I recommend avoiding this option unless your machine has absolutely no way to take 12 volt power directly. Inverters can be notoriously inefficient; some models waste 40% of your battery power. Further the AC power put out by the really cheap inverters can burn out your CPAP power supply. Avoid them if you can. If you have no other option, then be sure to look for an inverter that is specified to run laptops, and expect to spend over $75. An acceptable (i.e. won't burn up your equipment) unit is:
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 should 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 CPAP, such as charging miscellaneous electronics, be sure to account for the extra amp-hours when you size your battery. You can charge a cell phone without much notice. When you get to your laptop however, that will draw a lot more power, which means you'll need a bigger battery.
And remember: the battery can also be used 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. You CPAP will be taking that smoky 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 once 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 some way to transport your battery to the charging station. Batteries of this capacity weight 50 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 power 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 14 amp-hours overnight, you'll probably need 20 amp-hours to get your battery back to where you started. Keep this in mind as you look at options.
Also remember that we do 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 get 20 amp-hours, you'd need to use the panel for 200 hours. Not nearly good enough.
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 likely to be at the low end of what we need and the cost is getting up there ($400+).
To generate enough power and still 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. To generate enough power, we're looking at panels that start about 16 square feet and up - that's a 4 ft. x 4 ft. or larger square panel that you'd have to 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.
There are several elegant wind power systems designed for RVs or sailboats. The Air-X 12 volt wind generator works extremely well in winds starting at 7 miles per hour and can easily produce enough power to handle a typical CPAP, plus other equipment. Expect to pay $750 for the generator, plus additional cost for the hardware to get it safely up in the air, plus you'll still need a battery. However, you should also expect it to look horribly modern. It's also not silent. Wind generators make a 'whisk-whisk' noise that other campers might find objectionable. It's unlikely that you would get sufficient wind unless you're camping on the Serengeti. For both the solar and wind options, be prepared to negotiate with your camping neighbors.
You can feel free to contact me if you have questions or ideas. I can be reached at:
preed [at] dnaco.net
phil [at] moyen.org
I'm also on Skype, but email first.
CPAP at Pennsic by Phillip C. Reed is copyrighted © 2011 and published under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. All official SCA publications are granted a license to republish this article without further permission from the author.
for more info and republishing details.
If this article is reprinted in a publication, I would appreciate a notice in the publication that you found this article in the Florilegium. I would also appreciate an email to myself, so that I can track which articles are being reprinted. Thanks. -Stefan.