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Old 08-27-2014, 05:55 AM   #1
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1994 34' Excella
Kalamazoo , Michigan
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12V power for CPAP machine.

For boondocking, I tried to set up a small inverter to provide power for my wife's CPAP machine in our RB setup. Actually, I tried a 200w, then a 400w inverter, with the same result: the inverter faulted out with a low battery voltage warning. The machine is only rated at 125w, so I am thinking that the starting load is quite a bit higher, and the voltage drop from the front to back of the trailer might be enough under high transient loads to cause the fault. The inverters work fine up front...I use the bigger one to run the TV and DVD player.

A friend suggested that adding a small marine AGM battery near the inverter might help buffer the load, and serve as emergency backup should we lose power. I'm not sure hooking it directly to the 12v lines is good since I don't have any way to control the charging current. Right now my base plan is to buy a small 4 stage charger ($30 on Amazon) and charge the battery from shore power.

The ideal solution would be a relatively small and cheap 12v converter that would manage the charging, whether from 12v or 110vac. Does something like this exist? Any better ideas how to do this?

FYI..I can buy a solution from the CPAP machine company that does battery backup....$500. I'm highly motivated to find another way!


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Old 08-27-2014, 06:12 AM   #2
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We have a front bedroom model where the factory supplied inverter is actually located under the queen bed so we added an inverter outlet next to the bed for my CPAP. It works fine. You might want to see if an inverter outlet which would work off the factory inverter can be installed by the bed for your wife's CPAP. Depending on where the inverter is located, this might be an affordable option.

Bob Martel
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Old 08-27-2014, 06:28 AM   #3
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1994 34' Excella
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Forgot to mention that our 94 model does not have a factory inverter, Bob. But thanks!

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Old 08-27-2014, 06:33 AM   #4
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What is the brand and model number of the machine and the optional battery backup? If you have them, post a link to specifications and/or owners manual.

An dedicated AGM battery for the machine, tied into the Airstream AC circuit but isolated from other current drains, may be an good option.
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Old 08-27-2014, 06:52 AM   #5
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Most CPAP machines operate on DC voltage, but have a "brick" transformer for household 120V use. You may be able to find a suitable 12-24VDC power supply for your CPAP that will plug into the 12V outlet in the bedroom.

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Old 08-27-2014, 07:18 AM   #6
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Check with the supplier of the CPAP machine, they should have a DC adapter and cord. We obtained one for ours.

Bill Kerfoot, WBCCI/VAC/CAC/El Camino Real Unit #5223
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Old 10-11-2014, 11:26 AM   #7
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Boondocking with a CPAP

I found power accessories for my (Respironics) CPAP Machine at CPAP Machines and CPAP Masks for the Treatment of Sleep Apnea.

I added a 12 volt DC power jack connected to a spare fuse in my 7300 Parallax converter. This way I'm able to connect directly to the battery without going through any converter. The less that you " convert" a voltage, the more efficient your circuit will operate, thus longer battery life.

When cooler weather entices me to use the propane furnace, I operate my CPAP machine from a stand alone battery. Knowing that the furnace blower motor will be my largest battery load (when Boondocking) I'm able to extend my hours of usage by not adding the CPAP too.

Due to occasional utility power outages at home, I wanted a reliable backup power supply which was portable and could be used for Boondocking as well.
I selected a 12 volt, 35 Amp hour, sealed Glass Mat rechargeable battery.
After two (2) nights of use while Boondocking, I continued to use the battery (with the CPAP) for three (3) more nights. [ Note: I turn the humidifier OFF to conserve battery run time]
So, after five (5) nights of use, I connected my Multi- stage charger to the battery and found the percentage of charge at 65 %.
[ Solar ( brand name) Charge It! Model #4512 12 volt, 2/6/12 Amp multi-stage, multi-battery type charger]

The trade off with using a larger 35 Amp hour battery is the weight (22 lbs.)
If someone was only interested in 1-2 nights of backup power, you could get by with a smaller/ lighter battery.

I'm learning that CPAP use is increasing so it appears there are more options available for alternate power sources. Lithium- ion batteries may prove to be the better choice eventually.

Happy Boondocking my fellow CPAP'ers!

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Old 10-11-2014, 11:47 AM   #8
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I have a Respironics CPAP also. I obtained a 12 volt cord that plugs into the 12 volt socket in the bedroom of the trailer and directly into the machine. I run it this way when not hooked to shore power. I have also run it with a very low wattage inverter, something like 35 watts, from Radio Shack. When I run it on the RS inverter I set it so that it does not heat. When I need to go several days boon docking I also usually turn the heat on the CPAP off. But it is not really necessary. We now carry a generator and I can keep the trailer batteries charged as needed. I keep both the 12 volt cord and the 110 transformer that came with the CPAP plugged into the the trailer in the bedroom so all I have to do is to switch which one is plugged into the CPAP based on whether we are hooked up or not.
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Old 10-11-2014, 11:54 AM   #9
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I have friends with both CPAP machines and Oxygen generators. I have measured the 12 volt power consumption for both systems.

I have found the CPAP machines, operated on 12 volt power directly take in the 1 to 2 amp range, which is pretty minimal. The amount depends on the settings and the brand of course.

The Oxygen generator my friends use in the car, while traveling, takes far more current. In the continuous mode (which she needs) the consumption is in the 8 to 11 amp range, which is pretty substantial on a 24 hour basis.
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Old 10-12-2014, 12:51 PM   #10
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My solution for my husband's C-Pap needs while boon-docking (which is pretty much the way we like to camp) has worked out perfectly and not too expensively. 400 W pure sine inverter directly connected to Optima battery (battery for coach, not a separate one for CPap) When we tried plugging the inverter into the 12v outlet, we got a low battery warning in the middle of the night. So it made a difference to have the + & - leads from inverter directly connected to the battery. A 100W Grape solar panel from Costco successfully re-charges the battery during the day and it is ready to go again by evening. He is even able to use the humidifier on the C-pap & makes it through the night & beyond. We have used this for many (6) days of dry camping & even on cloudy days, battery charged rapidly. So happy not to have had to buy a generator or any of the costly C-pap battery packs out there. this set-up was much cheaper & efficient & quiet. Please, note. my AS is a '62 GT that I gutted & remodeled. Nothing in it is original factory and we use very little power. i.e. no TV, DVR, etc.
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Old 10-12-2014, 04:45 PM   #11
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My wife's CPAP is a Respironics. The machine runs off 12 volt DC. The box that plugs into the wall and then into the machine provides 12 volt DC power to the CPAP machine. The nurse told us that these machines are setup so truck drivers can plug them into the dash when sleeping on the side of the road. I bought a lighter plug adapter at Radio Shack and plug the CPAP into a 12 volt outlet in the AS bedroom when 110 AC is not available. We have been running like this for over two years now.

Inverters that convert DC to AC use up a large amount of power in the conversion process. Check to see if your CPAP actually runs off of 12 volt DC. If you want to get the most out of your battery, run your CPAP directly off a 12 volt DC battery when AC is not available.
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Old 10-23-2014, 10:20 PM   #12
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My accidental boondocking CPAP experience

I just returned from a 2400 mile trip to Madison WI from Tyler Texas, and after a week I made a swing by Elk Grove Village on my way back home to have some awnings installed at ZipDee. They asked me to arrive on Monday for measurements and then would install on Tuesday. All of a sudden I realized that I wasn't going to have a way to run my CPAP machine and had planned to boondock beside their building. Called my CPAP supplier in Tyler Texas and they checked with their Elk Grove office and had no inverter in stock. My supplier suggested as a cost savings...going to a local Radio Shack, so that's how I was able to get the therapy overnight. I used the inverter two more nights on my way home. In fact I also boondocked in a hotel parking lot and ran the central furnace as it was 36 degrees outside. I had previously used the CPAP without the heater humidifier and breathing ice cold air over ice cold water is pretty hard, so I turned the humidifier heater up to it's highest setting and slept comfortable for several hours before hitting the road again. Nice to search and read the posts of others who also have to use CPAP. I know I bought the inverter which has a 110 plug in, a phone or lap top USB charger connection and a few other feature but now that I realize the CPAP is only 12 volts and I could have plugged it directly into the wall cigar lighter if I had had the 12 volt cord for my unit. Again impressed with my Airstream and it's capability to make me feel comfortable away from home!!!
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Old 10-28-2014, 09:27 AM   #13
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If you have to run wires, the power losses over the 12 volt DC wire would be much higher than the losses over a 120 volt AC wire. In other words, it'd be easier to wire up an outlet (or a long extension cord!) than running a heavy wire for the inverter to connect to by the bed.

I don't have a CPAP, but surely this is a much simpler solution than converting to 120 volts only to convert back to low voltage. (As I said in another thread, my limit is one power conversion.) I realize there are likely many different models, but that one popped up in a very quick Google search.
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Old 10-29-2014, 06:24 PM   #14
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I buy all of my CPAP supplies at Super service, great website, and yes they do make a 12 power supply for Respironics machines. It is what I use for mine in our AS and it works great! It is also handy for when the power goes out at home, for which I have a 35AH AGM battery on standby for "just in case".

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