Power Inverters for CPAP Machines

Published: 09th February 2010
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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. He thought it would be helpful to write an article 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.

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 http://theinverterstore.com/the-inverter-store-product.php?model=pwri60012s 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 modified 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.

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.

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