I am going to buy a travel trailer. I use a CPAP machine at night to breath because I have sleep apnea real bad. If I don't use the machine I wake up or choke 50 time each hour. My ResMed pump says it takes 2.5 amps on wall power. If I stop at night and have only battery power, what is the best option to power a CPAP machine? If I buy an inverter, will the inverter kill my battery before morning? Last question: Does the car recharge the trailer battery or do I have to use park power and the trailer's converter?
i too use a cpap and my rv came with a 12v plug in the bedroom i bought a $10 converter and plug it in to the 12v and then plug my cpap to converter works perfect no problems with running battery down one night we ran the furnace with no battery problems ,,,,,,,,,,,,,,,,,,,my trailer only has 1 battery no problems...
* This post was
edited 02/11/13 08:11am by N2SNOW2 *
I as helping a friend dry camp with a CPAP machine. He had 4 batteries, and would use most of the power by the third night, and had installed a 400 watt solar system to recharge the battery each day. So basically his energy use was higher than the 400 watt solar system would make up, and he needed to run a generator to keep the battery full.
However he also ran laptops and other things in the RV that used power, so it was not only the CPAP running the battery down.
Your machine is probably rated to use less than 2.5 amps, and that figure is only there for sizing reasons. So say it is in a rest home, they will not put 10 on one circuit breaker and hope it does not trip each night at midnight.
Your actual amp draw is probably about 1 amp at 120 VAC, with a little more when the humidifier is on, a little less when only the fan is running. You can save power by filling it with warm water, say 100F or so. The electric heat element will take 300 watts to boil 1 pound of water into a vapor (at about 85 - 90F).
Each group 27 battery will hold a maximum of 100 amp hours at 12 volts, or about 1200 watts. You should really only use about 1/2 that power, because depleting the battery to 10 volts is not recommended for long battery life, less than 11.5 volts will probably not let the furnace run, the lights will be really dim, ect. and the inverter might cut out at 11.5 volts too.
I would recommend 3-4 batteries. If you go with golf cart batteries, they will last the longest, with proper care, my first set lasted 13 years, and I gave them to a friend who kept using them. My second set was not cared for well at all, and only lasted 6 years. Gold cart batteries are used in pairs, 65 pounds each, and 220 amp hour rating for the pair at 12 volts. THey last so long because they contain a gallon of water, and lots of lead.
You can also save a lot of power by finding a 12 volt DC CPAP machine. There are many, and even the one you have might be a 12 volt model with a 120 volt power cord to a transformer to the machine, you can check.
Anyway 1 amp at 120 volts is about 120 watts per hour, and you can expect to use up 2 batteries overnight.
How quickly will the battery recharge while driving? About 10 amps per hour of drive time, or not very much. So a 8 hour drive might transfer back 80 amp hours of power to the battery that you used 110 amp hours out of it in 8 hours of running the CPAP machine + 35 amp hours to run the refrigerator, CO and propane detectors, and other things in the RV in 24 hours. Chances are you are not going to be driving a full 8 hours.
In a motorhome, things look much better, with #2 wire going from the 120 amp alternator to the battery, it can be full in as little as 4 hours of engine run time. The factory installed wiring to the trailer wiring harness is only #12 wire, rated at a maximum flow rate of 20 amps (will blow a fuse at just over 20.3 amps) but with internal resistance, it actually limited to about 10 amps flow. Upgrading to #8 wire or #6 would work, and then install a 30 amp twist lock connector at both the RV and truck ends, with a #10 SO cord between them to give less resistance to the charging circuit. This might allow up to 30 amps to transfer into some weak batteries, but after a couple hours towing, the RV battery will be fairly full, and at say 12.5 volts, while the alternator 40' away is putting out 13.3 volts, and barely anything will move because the wire resistance and voltage drop, with both batteries about the same charge on them.
So I might recommend a solar system. The panels have come down in price recently, where a 150 watt panel is about $175. Two of those, and you will have a great charger for the trailer, that will make up for the lack of good charging from the truck.
Your TV should charge the TT battery while towing if you have a 7 pin plug, though not too fast. Some TV's need a fuse or relay installed.
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My CPAP machine draws 2.5 amps without the humidifier running. 4 amps with the humidifier. I put a 12 volt outlet beside the bed so that I could plug it in without the need for an inverter. I had to buy a different plug for it though. It uses a good amount of juice each night, but we have yet to run out of battery by the morning even if the furnace did kick in a few times.
I also use a CPAP and it will run on 12 volts, so I wired up a circuit just for it. Previously I plugged it into the 120 volt outlet which was powered by our inverter/converter powered by four 6 volt deep cycle batteries. We never had any problems with either method while boondocking in over 10 years. However, I don't use the humidifier. They take quite a bit of power to heat the water, so that has to be a factor. Still, I think four batteries would take care of your needs for one night if not several nights.
In our stick house, I built a battery backup to keep the CPAP working in the event of a power failure. The backup uses a 12 volt tractor battery from Costco and is kept charged by a automatic battery tender. It stays connected 24/7 and works fine. I would suspect the battery would only last one night, but that's not a problem for me.
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If your cpap has a brick in the power cord, it is probably running off of 12v already. Get a 12v cord from some place like cpap supplies USA and install a 12v receptacle near the bed. On some machines, you can use the humidifier in "Passover" mode, drawing some moisture into the air without heating the water and using more current.
If you can do without the humidifier, you will be fine with just a couple house batteries. If you use the humidifier, you will need 4 or even 6 golf cart batteries.
FYI, My CPAP uses about the same power as the 20" LED TV. With couple of good batteries, you will get by, but you will need to recharge every day using solar or a generator.
I have recently worked with a couple of Rv guys that needed this as well. This is what we did installing the small 400W-600W PSW Inverter close to the battery bank mounted on the vertical wall in the pass through storage area usually directly under the bed room. Then we ran two 120VAC extension cord drops from the Inverter, one to the home entertainment center location and the other 120VAC extension drop cord to the bedroom area. We used the WIREMODE cable management items from LOWES. All cables are out-of-sight with only the 120VAC 6-port receptacle showing at the back of a table top or cabinet top. the PSW Inverter is remote controlled from inside the trailer.
Small Trailer Typical floorplan
This is a great little emergency 120VAC Inverter system for when camping off the power grid. Highly reccommended to use a small generator with the trailer shore power cable plugged into it using a RV30A-15A "dogbone" type adapter (WALMART) to re-charge the batteries each morning when you are having breakfast and making coffee. using smart-mode charging it only takes three hours of generator run time to get the batteries back up to their 90% charge state.
This would be me using my 2KW Honda Generator sitting in the tailgate corner of my truck bed to re-charge my trailer batteries each morning.