Using a CPAP machine

**winddrinker** · 10-09-2018, 01:14 PM

As a result of some recent heart issues/surgery my wife now needs to use a CPAP machine. When we are at home the operation of the CPAP is not an issue. We will be traveling south this winter in our Reflection 29rs and we spend the majority of our time in boondocking situations. I have visited with the hospital issuing the machine and have also called the ResMed Air Sense 10 support line and they can not answer/explain the following concern.

The literature says not to use this CPAP with an inverter. They suggest using a converter and plugging into a 12 volt plug if you don't have AC power available. I have 410 watts of solar on my RV with four 6 volt batteries. Based on my calculation of amp hours needed for operation of the CPAP and the storage capacity of my batteries I don't see the problem with using my inverter to power the CPAP through the evening hours (approximately 10 hours & 50 AH). When I ask the hospital and the Res Med people why I can plug a 12 volt converter into my electrical grid but not the inverter they have no answer.
I know there are MANY rv'ers out there that have CPAP machines and I suspect many boondock/dry camp as we do. What do you do? How do you operate your CPAP in these situations?
Jim McGrane
Helena, MT

**MarkDeb** · 10-09-2018, 01:58 PM

I've looked in to this for dry camping at music festivals.
Res Med documents (see battery guide 198103) seem to suggest they are most concerned about customers using 'dirty output' inverters (instead of pure sine wave) so they issue blanket 'don't recommend' to cover the possibility of failure. imo

**gbkims** · 10-09-2018, 02:05 PM

Some add a 12V outlet in bedroom - https://www.mygrandrv.com/fo...ll=1#post66321

**offtohavasu** · 10-09-2018, 03:20 PM

Much more efficient to run on 12v instead of inverter. I supplied this information on another thread related to this topic:

You can also look at the power consumption based on watts.

AC Power Consumption: 100 - 240 VAC, 50/60 Hz, 2.1 A = 252 watts (based on 120v)
DC Power Consumption: 12VDC, 5.0 A = 60 watts.

Additionally, if you're running the inverter, you have to calculate the loss you'll be getting with that.

For example, say you want to run on inverter for 5 hours.
Watt-hours = watts * hours = 252 watts * 5 hours = 1260 watt hours

Account for the efficiency of the inverter, say 85%

Watt-hours = watts * hours / efficiency = 1260 / 0.85 = 1482 watt-hours

Since watts = amps * volts divide the watt hours by the voltage of the battery to get amp-hours of battery storage

Amp-hours (at 12 volts) = watt-hours / 12 volts = 1482 / 12 = 123.5 amp-hours.

**JCR GD** · 10-09-2018, 03:27 PM

My wife has that same unit. I put a 12v DC plug by the bed by tying into the closet light. No problems, plenty of power.

FWIW if you use an inverter you are going from 12v DC to 120v AC and back to 24v DC, waste of power. The CPAP unit actually runs on 24v DC so the "12v adapter" just goes from 12v DC to 24v DC, much more efficient.

The "12v adapters" are available from several suppliers on line. Mine was about $60.

EDIT... Thanks Curtis

**powerscol** · 10-09-2018, 04:38 PM

https://www.mygrandrv.com/fo...highlight=CPAP

In looking at your unit the above post should help, It runs my CPAP easily all night. I only have 2-12V batteries and find it uses very little power. You will need to get the 12V plug adapter for your unit. One cam with my unit when I asked about it. Its a stand alone power cord. The plug location I chose works well. You should be able to see the flooring structure under the bed from the front compartment.

Hope this helps