C-Pap power usage

With only a very slight increase for the conversion, yes.

yes 7.4 at 12v = 3.7 at 24v but there will also be a slight conversion factor
so maybe 7.8 amps at 12v

I'm going to guess her's is a resmed. battery power solutions makes a great 12V to 24V DC to DC converter for these units.

I think a few added comments might be of help for anyone who is not familiar with RV CPAP issues. First, Res Med makes CPAPs designed to run on 110 volts and also other units designed for 12 volt use. The 110 units seem to use a lot of power and for battery use they would also require an inverter which loses additional power in the form of heat. The 12 volt units comes with a transformer and can be used with 110. I found many of the providers do not understand the difference. So you might actually need to research the Resmed offerings and give the provider the appropriate part number.

CPAPs can chew through a lot of battery power. According to the OP, his 12 volt model uses 6.6 amps. For 8 hours of use, that would be 53 amp hours. Two units running for a night would deplete the 200 AH batteries to less than 50 percent. The 6.6 amp draw sounds high and is probably the maximum with the humidifier running. My wife's unit pulls about 3 amps without the humidifier. Anyway, CPAPs pull a lot of power and if you are going to run a CPAP solely on battery power, you will need a substantial battery bank and you will need to run a generator or have a suitable solar system and plenty of sunlight.

There are some new travel units that require minimal power, but you would need to go back to your sleep doctor to discuss the suitability.

ktmrfs wrote:
I'm going to guess her's is a resmed. battery power solutions makes a great 12V to 24V DC to DC converter for these units.

Yes, I have ordered the Resmed 12v DC/DC to 24v converter. I am pretty sure the only thing I will need to do to get it fired up is fabricate a pretty stout 12 gauge, 12v extension cord to get from my side of the bed to hers.

JimK-NY wrote:
I think a few added comments might be of help for anyone who is not familiar with RV CPAP issues. First, Res Med makes CPAPs designed to run on 110 volts and also other units designed for 12 volt use. The 110 units seem to use a lot of power and for battery use they would also require an inverter which loses additional power in the form of heat. The 12 volt units comes with a transformer and can be used with 110. I found many of the providers do not understand the difference. So you might actually need to research the Resmed offerings and give the provider the appropriate part number.

CPAPs can chew through a lot of battery power. According to the OP, his 12 volt model uses 6.6 amps. For 8 hours of use, that would be 53 amp hours. Two units running for a night would deplete the 200 AH batteries to less than 50 percent. The 6.6 amp draw sounds high and is probably the maximum with the humidifier running. My wife's unit pulls about 3 amps without the humidifier. Anyway, CPAPs pull a lot of power and if you are going to run a CPAP solely on battery power, you will need a substantial battery bank and you will need to run a generator or have a suitable solar system and plenty of sunlight.

There are some new travel units that require minimal power, but you would need to go back to your sleep doctor to discuss the suitability.

I am thinking that the Amp draw on the labels that I posted are with the Humidifier in use. Since running two machines(my trailer unit and my house unit) w/o humidifiers on drops me to say 12.4 volts. 12.6 volts is 100% charge right?

Most likely. Most CPAP/BiPAP machines consume around 1 amp @ 12VDC,
per hour, without humidifier.

Voltage is a very poor indicator of battery state of charge. A good battery monitor will tell you what is going on.

I use a res med vpap. I called Res Med and was told I could operate my machine (two different models over the years) on 110 volts RV modified sign wave inverter. They did say to remove the water tank or shut it off.(depends on the model). I've used it this way many times over the years when we are not plugged into electrical power without problems.

I have a 300 watt pure sine wave inverter and a ResMed CPAP/APAP that draws 3.75 amps at 24vdc. I calculate this to be 90 watts. The plan is to use the CPAP's 120vac adapter that came with the unit and the inverter hooked to my 12v battery. Does anyone see a problem with this? The alternative is to purchase a 12v to 24v adapter for $68 which I would like avoid.

The inverter will work. The DC-DC converter would most likely be somewhat more power efficient, maybe somewhere in the vicinity of 20% overall, and perhaps quieter if the inverter has a cooling a fan. I suspect in your case the power consumption may not be of much practical concern as you'll probably have to recharge the RV batteries daily in either case.