CPAP on battery power

Using a battery to run your CPAP machine is something that everyone eventually wonders about, whether you're planning a camping trip or just worried about an outage due to a storm. Your CPAP machine can be run on a battery, but the details of how to do so depend on the brand of CPAP machine. And the type of battery you'll want depends on the conditions under which you plan to use it. Any battery that you use will eventually need to be recharged or it'll stop working. And regardless of your situation turning off the humidifier on your machine will help save battery life as the heater used to warm the water in the humidifier is by far the biggest energy draw.

The amount of charge stored in a battery is measured in amp-hours. If you have, for example, a 20 amp-hour battery that means that you can supply 20 amps of electric current for one hour, or 10 amps for two hours, 5 amps for four hours, and so on. The number of amps times the number of hours gives you the electric charge measured in amp-hours. The greater the number of amp-hours the longer your battery can run without needing to be recharged.

The rechargeable battery with the largest number of amp-hours is the lead-acid deep cycle marine battery. These batteries are heavy and bulky, so if you desire something more compact or light weight you will have to sacrifice amp-hours to get it. One good alternative to lead-acid batteries are lithium-ion batteries.

Another factor to consider is the type of electricity needed for your CPAP machine. Is it ac or dc? And how many volts does it need? Batteries supply dc electricity, the electricity in your home is ac. Most CPAP machines require 12 volts or 24 volts. The electricity in your home is either 120 volts or 230 volts. When you have your CPAP machine connected to the electricity in your home the machine has takes care of converting the electricity for you, so you don't have worry about it.

In the case of Respironics machines the 120 volt or 230 volt ac electricity in your home is converted to 12 volt dc electricity. You can therefore connect a Respironics CPAP machine directly to a 12 volt battery with the appropriate power cord.

Many manufacturers will sell you a battery pack that will change the dc electricity of its battery to the ac electricity normally provided in your home. This is referred to as an inverter.

Do It Yourself Battery Pack Instructions

While there are all sorts of places that sell small battery packs for CPAP, they invariably only run the machine, not the humidifier and have a limited runtime. Some even use "disposable" batteries and can use a dozen D-Cells per day.

This is a "how to" for putting together an awesome (semi) portable power source for a long weekend, for about $140.

Exide Stowaway Deep Cycle Marine/RV/Deep Cycle Battery, 27MDCST 105 Amp-Hours $90 @ Tractor Supply Co.

Battery Box (plastic box to hold battery and keep things from touching the terminals) ~ $20 @ Tractor Supply

400 Watt 12VDC -> 120VAC Inverter $28 @ Harbor Freight

This will run my CPAP machine (Respironics System One) for more than 24 hours on a single charge, with the humidifier on high.

It's great for places where you can park within walking distance of your car, and on hot nights will even run a fan inside your tent.

A few notes:

• If you're not too far from the car, you can leave the battery and inverter in the car and just run an extension cord to the tent.

• You'll need a small 12V battery charger. I didn't list it because a lot of people already have one, but if you need one, they're cheap at Harbor Freight.

• This system produces 120VAC, which means you get to plug in your normal CPAP power supply, just like at home.

• There are systems that will run your machine directly from a 12 volt battery, however I don't like them for two reasons:

1. 1 If you connect your CPAP backwards, you'll destroy it
2. 2 All batteries lose voltage over the course of the night. Running your machine with it's normal power supply allows it to compensate for any variations, which is not the case when running on 12 volts.

• The vendors above were the cheapest widely available sources for the needed components that I found.

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