The Inverter Store Blog

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.

It does not matter if you are running a 12 Volt, 24 Volt or 48 Volt system. You have probably had a conversation with someone about your battery bank. The main question that people always ask is do you keep your batteries in Parallel or Series?

For those who might not understand these terms, let me explain them for you.

Batteries in Parallel, means that the batteries in your bank are connected so that the inverter thinks they are all one big battery. Meaning if you connect four batteries 12V in parallel your inverter, still sees one 12 volt battery. Your power source is still 12 volts and your amp hours are quadrupled.

Batteries in Series, means that the batteries in your bank are connected in a way that the volts are doubled, for each series of batteries. To keep this simple, two 6 volt batteries in “series” are 12 volts. The power inverter recognizes them as a 12 volt power supply.

Now that we have a basic understanding of series and parallel. Your next question is probably which one is the better connection?

Well, that depends on your system. How many batteries are in your bank? What voltage are they?

Most battery manufactures recommend no more then 4 batteries be connected in parallel.

One point I would like to share is that if your batteries are in parallel, and one of them fails, the whole bank might stop putting out power. If the batteries are in series, if one battery fails, then just that “cell” or group of series batteries will stop producing power. So if you have a large battery bank, series is definitely the way to go.

For more information on Battery bank connections, please see our PowerPoint presentation at the link below.

Battery Connection PowerPoint

Theinverterstore.com offers excellent customer support and we would be happy to answer any questions that you might have. We have a wide selection of pure sine wave and modified sine wave inverters and our goal is to make sure our customers are purchasing the right equipment the first time around.

If you are reading this post, you either own a pellet stove and have spent a couple of nights in the cold because you had no power. Or you are thinking of buying a pellet stove and you want to know how to avoid a cold night without your primary heat source. We will help you choose the right power inverter and battery to keep your space warm and toasty for the duration of the power outage.

With some research, I have found some valuable information about pellet stoves. Most pellet stoves plug directly into your standard wall outlet. They use about 1.0-1.3 AC amps per an hour. In general they have a start up usage of about 4 times there continuous usage, or between 4 -5 AC amps. We need these numbers to find out how much back up power we will need. You can find them in your owners manual, under the section usually called “Electrical Rating.”

Now that we have our basic set of amp usage, we should design a sample back up system. Which means we get to do some math, we will try and keep it simple.

The maximum AC amps we will need is 4, this start up amperage is for a standard sized pellet stove, one designed to heat up to 2500 sq ft. We need to convert this to watts, to do this we will multiply AC amps x 120 volts. We use 120 volts because this is the power of the outlet in your home.

4 AC amps x 120 vac = 480 watts

We now know that 480 watts is our maximum usage.

The stove will run at 1.1 AC amps continuously.

1.1 AC Amps x 120 vac = 132 watts

Ok now we have the numbers that we need to choose a power inverter.

I have some research and have discovered that some pellet stoves, require a pure sine inverter in order to operate. This is something you will have to ask your dealer before purchasing the stove. There are some pellet stoves that will operate off of a modified sine inverter, once again this is manufacturer specific. I will make a recommendation for a pure sine power inverter, because it will work on any pellet stove.

For this set-up I would recommend the AIMS 600 Watt Pure Sine Power Inverter. This inverter falls in to the range of maximum inverter efficiency. Some devices require a pure sine wave to work properly, most devices work more efficiently with a pure sine inverter. A pure sine inverter makes your device work more smoothly and can increase the lifespan of the device.

Now that we have an inverter we need to select our battery and charger. I am going to recommend our Lifeline 12 Volt Deep Cycle Marine AGM Battery. I am recommending this battery for a couple of reasons, first of which is power. This deep cycle marine battery has 105 amp hours and can handle many charge and discharge cycles, unlike an standard car battery. The second reason I recommend this battery is because it is an AGM or absorbent glass mat battery. This means there is no risk of the battery spilling or leaking inside your house. Also AGM batteries, do not need to be ventilated, because they do not emit dangerous gases, like many other types of batteries. These Lifeline AGM Batteries also charge 20% faster then a conventional vented battery or a gel cell battery. These batteries are essentially 100% maintenance free, no addition of water is needed. There are other types of deep cycle marine batteries, but this is the best for our application.

Next we need to select a charger, I recommend the Iota Smart Battery Charger/Converter. This charger is a 12 volt, 30 amp charger. It is also a “smart charger” which means it will charge your batteries quickly and keep them fully charged, without overcharging and damaging the battery.

Lastly you will need a transfer switch, we recommend our Iota 2 Way Automatic Transfer Switch 30 amp. This transfer switch is for inverters 3600 watts or less. This not necessary, but it does automate your back up system. Meaning that if your power goes out in the middle of the night, your back up will automatically keep your pellet stove running.

Lets take a moment and review which parts are included in our system now:

• AIMS 600 Watt Pure Sine Power Inverter

• Lifeline 12 Volt Deep Cycle Marine AGM Battery

• Iota Smart Battery Charger/Converter 12 Volt/30 Amp

• Iota 2 Way Automatic Transfer Switch 30 amp

I have another AIMS product that is a pure sine power inverter, charger and transfer switch in one unit. It is our AIMS 1500 Watt Pure Sine Power Inverter with Built in Transfer Switch & Charger. This product is designed for those who want to simplify their install. You will still need the battery mentioned above to use this device.

The last item you will need to install this system is cables. It is important to get the right cables, that way you get the maximum power from your back up system. Fro either on of these systems you could use a 4 AWG or larger cable, also known as a #4 gauge cable. I recommend that you follow the stove manufacturers instructions, when deciding where to place your battery. In general most manufacturers recommend the battery is at least 6 feet from the stove, in a battery box or ventilated cabinet. Keep in mind that you want to keep the inverter as close to the battery as possible, for maximum efficiency. If you are going to place the inverter more than 6 feet from the battery, we recommend you use a larger cable, to decrease bottlenecks, the size we recommend is 1/0 AWG. We sell both of these cables on our website theinverterstore.com. To keep it simple you can just use a longer extension cord from the inverter or the transfer switch to the stove. This way you can keep the battery far from the stove and the inverter close to the battery.

I have included some simple layouts of how this system should be hooked up. Of course if you have more questions, please let us know we are happy to help.

The first layout is the system with the AIMS 1500 Watt Pure Sine Wave Inverter, Charger with built in Transfer Switch.

AIMS 1500 Watt Pure Sine Inverter Charger with Transfer Switch

This second layout is for the system that we built up around the AIMS 600 Watt Pure Sine Power Inverter.

Inverter with seperate transfer switch and charger

If you have any further questions about power inverters, cables or batteries. Please give us a call @ 888-417-8673.
Theinverterstore.com offers excellent customer support and we would be happy to answer any questions that you might have. We have a wide selection of pure sine wave and modified sine wave inverters and our goal is to make sure our customers are purchasing the right equipment the first time around.