Wiring for cpap machine

[Oregon Fun-Guy]

need to support 20 amps per hour of current demand... quite a bit. Actual is probably a bit less, but I'd plan for 20 amps.

Dadeo6472 Doug, The amount of power you will need is dependant on the air pressure setting you have and the type of heated hose you have. Resmed has developed a document that gives a more accurate estimate of your actual set up. Here is a link to the page. (see page 7). An example of the calculation would be 12v amp hours from the table times number of hours of sleep times the number of machines, or 4.18 amp hours X 8 hours of sleep X 2 machines = 66.88 amp hours per night.

Another battery solution would be to use a battery pack made for powering CPAPs. An example of this type of equipment is found here. There are many other brands of these battery packs. I would suggest calling the customer service people at the example as recommended by a trusted information source.

[Dadeo6472]

From the looks of the RESMED documentation it looks like we need to swap up out our deep cycle battery for two high quality deep cycle batteries when we are boondocked overnight on a long trip. I can recharge them either by using the 3000 watt generator for a few hours or by driving 8 hours. This looks doable, since I have the generator I can always use that to recharge the batteries.

[Oregon Fun-Guy]

I can recharge them either by using the 3000 watt generator for a few hours or by driving 8 hours.

Sounds like a workable plan. One thing I considered doing for charging the batteries is to turn the battery disconnect to off and running a separate power cord from the generator to a battery charger to charge the batteries. The battery charger could put more of a charge into the batteries faster than your trailer's converter will put in. Your generator has enough power to run both the trailer and a separate charger. When you are through charging batteries turn the disconnect switch back on. I found that the newer battery chargers are built for three stage charging. I have a little NOCO 10 amp charger that works well for this.

Norm

[boyscout]

Resmed has developed a document that gives a more accurate estimate of your actual set up. Here is a link to the page. (see page 7). An example of the calculation would be 12v amp hours from the table times number of hours of sleep times the number of machines, or 4.18 amp hours X 8 hours of sleep X 2 machines = 66.88 amp hours per night.

Thanks Norm, just looked at that document, very helpful. I guessed above at @Daddeo6472 power requirement based on the 104 watts max specified in the user manual. Typical use is WAY less - future readers should discount my advice above and download the manual Norm has linked.

[Cate&Rob]

Some thoughts on how much battery capacity you need to support this . . .

If you are using lead/acid batteries (doesn't matter if they are flooded or AGM) you should size the bank such that you can meet you overnight requirements with 30% of their rated capacity. The reason for this is that discharging these batteries below 50% will damage them and charging above 80% takes a long time (meaning a lot of generator run time). You cannot force a lead/acid battery to absorb charge faster than its natural rate. Between 50% and 80% is the bulk charge phase where recharge is accepted quickly.

So . . . if you have two 6V batteries in series to make 12V, the capacity is not doubled, but stays at the capacity (in amp hrs) of one of the batteries. Probably about 220 Ah for good batteries. 220 x (80%-50%) = 66 Ah.

Rob