I recently received two DeVilbiss CPAP’s, these units were sent to us for testing direct from the manufacturer. We did some bench testing to find out what the maximum power usage is for each machine.
The first machine we tested was the DeVilbiss IntelliPAP AutoAdjust CPAP System. We tested this system here in our office on our DC power supply. All the testing was done at 12 volts. According to DeVilbiss, all of their CPAP’s will run on a modified sine wave power inverter. The specs call for at least a 200 watt power inverter, we used an AIMS 400 watt Modified Sine power inverter for this testing. We connected the inverter directly to the battery with cables, we did not use the cigarette plug. We decided not to use a cigarette plug, for one main reason. The manufacturer specs calls for a 200 watt inverter and a cigarette plug only handles up to 180 watts, if it is fused at 15 amps. If your vehicle has 10 amp cigar plugs, you can only go 120 watts maximum.
The first test was done for about 4 hours with the heater set at 10 and the CPAP set 20 cmH2O (maximum pressure). While monitoring the usage, I observed DeVilbiss IntelliPAP AutoAdjust CPAP System with the heater set at 10, consumes just under 8 DC amps per hour, maximum. The usage actually varies between 6.0 dc amps and 8.0 dc amps. We are going to use the max usage of 8 DC amps, this will give us an accurate amount to calculate battery capacity needed. Many people may be asking how do I convert DC amps to watts, etc. I will cover this after all the testing information is covered.
The next test I did with the DeVilbiss IntelliPAP AutoAdjust CPAP System, was with the heater off. The usage is lower, between 1.8 and 2.0 DC amps. We did not observe as much fluctuation in the usage as with the heater running. This makes sense, because it is constantly working to keep the humidity water at a certain temperature, causing the usage to cycle up and down, while maintaining the water temperature. The max DC amp usage, with out the heater on the DeVilbiss IntelliPAP AutoAdjust CPAP System was 2.0 DC amps. This system actually runs at a very low usage, with out the heat and humidity, about 24 watts.
The second DeVilbiss CPAP system we tested was the IntelliPAP Bilevel S CPAP System. This machine has two functions, IPAP and EPAP. We only need to understand these functions in simple terms, it has two settings “inhale” and “exhale.” The “inhale” or IPAP pressure setting on our test unit was set at 20 cmH2O and the “exhale” or EPAP pressure was set to 12 cmH2O. As far as I understand the machine pushes more air on inhale and backs off the pressure on exhale, to help the patient breath out easier. These cycles make the machine run a little bit different than the auto adjust, it uses a little bit more power. I also tested this unit on the AIMS 400 watt modified sine power inverter. In our testing with the DeVilbiss IntelliPAP Bilevel S CPAP System, we observed the maximum usage of this system with the heater set to “10″ to be just under 10 DC amps. The actual usage varied between 7.6 and 10.0 DC amps.
The next test we did with the Devilbiss IntelliPAP Bilevel S CPAP System was with the heater set to “off”, no heater. The maximum usage without heat on the DeVilbiss IntelliPAP Bilevel S CPAP System was just under 5.0 DC amps. The actual usage fluctuated between 0.6 and 4.9 DC amps. We will go with 5.0 DC amps to be safe.
Next I want to review our maximum usage totals and make some recommendations on which power inverter and a battery to use in your mobile system.

We will make one small conversion while reviewing our data.
To convert from DC Amps to Watts, we need to multiply the DC Amps by the voltage of our system, in this case 12 Volts.

DC Amps X 12 = Watts

DeVilbiss IntelliPAP AutoAdjust CPAP System maximum usage with the heater set to “on” and at level 10 and pressure set to 20 cmH2O (maximum pressure) was 8 DC Amps or 96 watts.

DeVilbiss IntelliPAP AutoAdjust CPAP System maximum usage without the heater, heater set to “off ” and pressure set to 20 cmH2O (maximum pressure) was 2 DC Amps or 24 watts.

DeVilbiss IntelliPAP AutoAdjust CPAP System, with a pressure setting of 12 cmH2O with the heater set to “off.” The max usage was 1.7 DC Amps or 21 Watts.

We used an AIMS 400 Watt Modified sine power inverter for all of these test. I direct connected to a battery for the test. I do not recommend that you use a cigarette plug for this equipment. Even though the watts are low enough for the plug to handle the load, most cables for cigarette plugs are not thick enough to handle the load. The cables for cigarette plugs are only rated at 80 watts per UL requirements. So to prevent damage to your vehicle, power inverter or CPAP, direct connect to the battery. You will get more efficiency this way also.

If you are using a mobile battery system, for example while camping. You need to use the DC amp usage to find out what size battery is needed to run this system. Lets run over an example, if you are using the DeVilbiss IntelliPAP AutoAdjust CPAP System, with the heater, your usage is 8 DC amps. A normal nights sleep is 8 hours, you will need at least 64 amp hours (8 dc amps X 8 hrs), to cover your daily sleep requirement. Most deep cycle batteries will give you 80 percent of their power before needing a recharge. I would recommend an 80 amp hour battery for this application. On our website we sell the Lifeline GPL-24T Deep Cycle AGM Battery, it has 80 amp hours. Just make sure you have provisions to recharge the battery during the day. For this application if you had the Iota 30 Amp 12 Volt Smart Battery Charger/Converter you could recharge this battery in just over 2.5 hours.

For the entire DeVilbiss CPAP product line, I recommend the AIMS 400 Watt Modified sine power inverter, per manufacturer specs they require at least 200 watts. I chose this product because a power inverter operates more efficiently with a smaller load, the closer you are to max output the less efficient the power inversion. This AIMS product will cover your power needs and give you the most efficiency out of your batteries.

I recently was contacted by Bob Stanton from A.W.A.K.E., Truckers for a Cause.
This is a non-profit organization that is dedicated to the health of America’s Truckers. Specifically A.W.A.K.E. is a network of people helping people with sleep apnea. Bob and I were discussing the power inverter needs for a CPAP machine. He thought it would be helpful to write a blog including any information that I felt would be useful. Having experienced sleep apnea myself, I feel obligated to share what I know. I hope the information that I have gathered during a couple of testing sessions, will be useful. Sleep Apnea is a serious health issue and we here at theinverterstore.com are dedicated to providing a solution for those who need to use a CPAP on the road.

I would like to let you know up front that if you have any information regarding another type of machine, let me know I am happy to add to this post at anytime. There are so many different types of CPAP machines on the market today, this is an open forum to share your knowledge, and hopefully gain some too.

The machine that I used for testing is the REMstar Plus with C-Flex. I have had this machine for a couple of years. It has the heated humidifier unit also. the power requirements for this machine are as follows:

REMstar CPAP w/C-Flex: 1 AC amp max

REMstar Heated Humidifier: 1.7 AC amps max

I am aware that this unit does have a 12 volt outlet on the back, but I am not going to use it for this test. I am going to run this machine for 3 separate eight hour periods off of an AIMS pure sine power inverter and a couple of 6 volt batteries connected in series. According to our information the max usage of the CPAP with heat and humidity is 2.7 amps or 324 watts. I found the watts with some simple math listed below.

Amps x Volts = watts

2.7 AC amps x 120 vac = 324 watts.

I think it can sometimes be deceiving to the user how much power there CPAP is actually using. Because the two pieces are stacked together. When you look at the bottom of the unit you see 1.7 ac amps. I thought this was the number. I always double check the manual and I discovered there were two manuals one for the REMstar CPAP w/C-Flex and one for the REMstar Heated Humidifier. There is a section in the manual that clearly states what the max power needs are, usually labeled “Specifications.” The information we need is listed as “AC Power Consumption.”

I was also able to do some research on the ResMED S8, ResMED S6 and C-Series Tango machines. According to the manufacturer they will run on the AIMS 150 watt modified sine power inverter, as long as you are not using humidity. If you are using humidity on any of these units, you will need to use an AIMS 300 Watt pure sine power inverter.

Field Test Results:
I ran the CPAP here at our facility off a small battery bank. I have ran it for 6 to 8 hours for 3 days straight. The machine operates great with the AIMS pure sine power inverter I used the AIMS 600 Watt Pure Sine for this test, because of the maximum power requirement. I also monitored the watts and amps this machine was pulling with a Kill A Watt monitor. I have found out some useful information. The usage for levels 4-10 with heat and humidity on, are very low right around or below 50 watts, the only time I noticed a higher usage was during startup. What I mean when I say “startup” is the energy used when the machine is warming up, I assume the extra watts were from the heating element warming itself up to temp. The usage level was at about 115 watts during startup.

I have found that the CPAP pressure level that is set up for me, does not reach the max output usage. If your settings are higher, than level 10 the usage could be higher on your machine. If you are in a really cold environment it could take longer for your heating element to heat up. I tested the startup in our warehouse, which is around 55 degrees.

We now know enough to choose a power inverter for this application. From the research that I have done most CPAP’s require a pure sine power inverter. I am going to use the AIMS 600 watt pure sine power inverter for this test. We are just above 300 watts, but even if we were at 280 watts, I would recommend the bigger inverter. For a couple of reasons. In the future you might have another device that you want to plug into this inverter. Having more power gives you room for expansion. Also power inverters run more efficiently when the load they are pushing is not close to max capacity. Running an inverter at max capacity is ok, but you get more out of your batteries when the inverter is more efficient. By more efficient I mean that the inversion is happening with less loss of power. This is because the inverter is running with less heat, when you run a continuous load on an inverter at or near max capacity you get a lot of heat, this makes your power inversion less efficient.

I have heard of people using modified sine power inverters with CPAP’s some run with no problems.

At least that you see, but I can tell you that a modified sine power inverter can make your device run harder and hotter than its supposed too. You may shorten the life span of the device by using a modified sine power inverter. I have heard from some truckers that their CPAP burned out prematurely because of the modified sine inverter. Although, some manufacturers state that their machines will run normally on a modified sine without strain on the device. Certain ResMed, models without the humidity feature can run on a modified. Also Fisher-Paykel states it has modifed its design to allow the CPAP machine to run on a modified sine inverter.

Bob Stanton from AWAKE, Truckers for a Cause has many years experience with CPAP’s in the field. He just let me know that he ran a Respironics in his truck off the 12 Volt plug, it drained his battery below 11.78 volts. Not only would his truck not start, the data that is required for DOT compliance was corrupted and the machine was in “service required” mode.

All Aims Power inverters have an alarm that lets you know you are reaching low voltage and will shut off, before draining the batteries to low to start the engine.

Bob has also has experienced personally a CPAP failing prematurely because he was using a modified sine inverter. He owned a Fisher Paykel from 2002-2005, the first machine failed within 18 months because the motor burned out, from the modified sine inverter, running it harder and hotter then designed. Fortunately, Fisher Paykel did warranty the CPAP machine.

The difference is in the technology of the power inverter. A pure sine wave power inverter, produces a cleaner power signal, one that is very similar to the power that you get from the outlets in your home. Complex and delicate electronics and medical equipment like the CPAP need cleaner power to operate properly and reliably. CPAP machines are not cheap and they are necessary medically, so I recommend you use a pure sine power inverter. According to the information I have gathered from the US DOT, there is some data, that is collected from these machines. There have been instances of this data being corrupted, because the user was using a modified sine, so stick the pure sine. This will insure that your CPAP works dependably on the road and at home for many years.