Being a CPAP user should not keep you from enjoying the outdoors for extended periods of time. What follows is a one stop guide for using a DC capable CPAP away from a wall outlet.
Check the user manual to make sure the CPAP unit you have is capable of running from of a DC power source (battery). Nearly all modern machines (2002-up) have some kind of built-in DC power capability. Most manufacturers have a section on power characteristics located in the back of the patient manual. Some manufacturers go as far as to give you some indication of your particular machine's power draw at a given pressure setting. When in doubt, contact the place where you purchased the unit, or the respective manufacturer for the specific information pertaining to your machine.
Now that you know you have a DC capable machine, it's time to decide how you want to hook the machine up. There are a several options here for you to consider. Most manufacturers have an optional DC cable available for their machines. This is by far the simplest method for connection and the one that offers the most flexibility. You will also need a 12v accessory plug (pictured right) to connect your machine to the battery. These can be purchased at stores such as Wal-Mart, Radio Shack and most auto parts stores for $6-$12.
Another option is a battery cable that connects to the machine on one end and has tabs or eyelets for connection directly to a battery, on the other end. This setup requires a bit more work because the eyelets rarely fit the size of the battery's terminals and may require a bit of modification. Puritan Bennett is the only major manufacturer, to my knowledge, that offers this option.
Yet another option is to connect the machine with the supplied AC power cord (the one that plugs into the wall at your home) to a DC inverter. This solution is the most inefficient because the inverter requires power for operation as well as your CPAP machine, so it will drain a battery faster.
Please note that if you do wish to use your heated humidifier with your CPAP on a DC connection, you will need a pure sine wave DC inverter such as the one pictured to the right. If you use your humidifier in a “Cool Passover” mode (no heat) then you do not need this product.
Now it's time to choose the right battery configuration. The most important considerations are: How many nights do you need the machine to run? Will you be using a heated humidifier? Will you be moving the battery and is there a place to recharge the battery? Most manufacturers suggest using a 12v deep cycle marine battery. These batteries provide power for an extended period of time and are best for non-mobile use (i.e. camping in one location, or use in an RV) because they are quite heavy, usually weighing 40lbs to 70lbs. Gel cell batteries are also a good alternative because they are much lighter, but they don't have the same capacity of the deep cycle batteries so they need to be recharged more often or multiple batteries must be used. These batteries can be purchased at stores such as Wal-Mart, Batteries Plus and most auto parts stores. You will also need to purchase a battery charger.
There are smaller sealed lead acid battery solutions available from some of the major CPAP manufacturers that are very well packaged and offer much flexibility and ease of use, such as the Respironics Portable CPAP Battery Pack, pictured right. These also need to be recharged more often than deep cycle batteries. Most include the battery charger.
Newer technology brings us high capacity Li-ion batteries that deliver a lot of power for a long time in a compact and lightweight package. The Super CPAP Batteries weigh between 3 and 4 lbs and can run a CPAP machine for as long as 40 hours (5 nights) on a single charge. These batteries come with a charger, carrying case and all the required connectors to power virtually every modern CPAP available. ResMed CPAP users will still need the DC-12 converter for the S8 Seies or the DC-24 Converter for the S9 Series, because their plugs run opposite polarity from other manufacturer's machines. The Super CPAP battery is available in three sizes, C-150 Wh, C-222 Wh and C-444 Wh.
How does one figure out how long the machine will run with a particular battery? This is a little complicated but we'll make it very easy for our purposes here. I am not an electrical engineer or a battery expert so what follows is a layman's explanation of how this works. A CPAP machine draws a certain amount of power during continuous use. That amount of power used is commonly expressed in Amp Hours (The number of amps used in an hour). This makes it relatively easy to compute the run time because conveniently enough, batteries are rated in Amp Hours too. Theoretically, if a CPAP machine draws 1Ah and you use a 70Ah battery, you would get about 70 hours of use (divide 70 by 1 = 70 hours of use). There is some variance due to different machine and electrical characteristics, but this is a good way to get real close without becoming an expert in electricity. I usually add .3Ah or .5Ah to the machine's Ah draw, as a cushion, and call it a night. I'd rather get more sleep that I planned as opposed to making coffee earlier than I planned.
You have your DC capable CPAP, the manufacturer specific DC power cord and a battery power source. Now that the hard part is out of the way; here is a very common hook up scenario. Bob is going to use his CPAP machine with his manufacturer specific DC cable during his three day camping trip to Montana . The camp site does not have any power available during the day to recharge a battery. Bob figured out that his machine, without humidifier, draws 1.43Ah at his CPAP pressure level. Based on that number he calculated that if he planned on sleeping 10 hours a night for 3 nights, he would need a battery rated at 42.90 Ah or greater (30 hours of desired use x 1.43 Ah draw = 42.90 Ah). He decided that going with a 50Ah deep cycle marine battery was the way to go, because he does not want to worry about recharging the battery daily and it also gives him some extra run time as a cushion if he wants to take a nap or get to bed early one day. To connect his CPAP to the battery he'll plug the male end of the DC cable into a 12v accessory plug with power outlet. This connector has a DC receptacle on one side and red/black clamps to connect to the posts of the battery on the other side. Connect the red clip to the red post of the battery, connect the black clip to the black post on the battery and sit back and revel in your accomplishment. It is that easy!
Also located in the power characteristics section of your user manual will be the power requirements for your machine. There are two basic standards for voltage and frequency in the world. The North American standard is 110-120 volts at 60 Hz, using plugs A and B, and the European standard of 220-240 volts at 50 Hz, using plugs C through M. Most modern CPAP, Auto CPAP and BiLevel machines will automatically detect and adjust to the differing voltages. So all you need is a non-powered plug adapter to convert the US plug to the style of plug used in country in which you are using the machine. These International adapter kits can be purchased nationwide at electronics stores such as Radio Shack or BestBuy . If you are not sure if your machine is capable of use outside the US, contact the place you purchased you machine or the manufacturer for more information about your specific model.