Mr. Rawles -
I have been living with a CPAP for many years now, and am one of the persons for whom it has worked very well. I also know how bad things can be after not having my CPAP for three days when an airline lost it. After three days I was almost totally non-functional and was ready to lay out the $2,000 out of my own pocket to get a replacement machine. Fortunately my machine was found by the airline.
More recently I had 3 nights in 2 months where power outages deprived me of the use of my machine. I determined that I needed to find a way to get my CPAP off the power grid.
The first step was to measure the actual power drawn by my machine. Using a Kill A Watt monitor I learned that my machine used 27 watts of power. This of course could vary with the pressure setting, and model used.
I then found a 55 watt solar charging system on sale at Costco for $200. The system came with 3 panels, mounting frame, charge controller, and 200 watt "modified sine wave" inverter. I added a 125 A/hr deep cycle battery,
battery case, and some 10 gauge wire. Since my CPAP did not have a DC power option, I could not run it directly from the battery. The AC input, however, was a "universal" design which can accept any AC voltage from 100
to 250 VAC without switching. Such a universal power input has no problem dealing with the less than ideal power from the "modified sine wave" inverter. If my CPAP had just a conventional 120 VAC power input then the
use of a "true sine wave" inverter might have been needed.
This system worked fine to run my CPAP all spring, summer, and fall, but come winter with shorter days and more clouds, it could not keep the battery charged. I needed to supplement the solar charging system with a AC powered battery charger.
The next year I purchased another identical system, and hooked two of the panels to the [batteries for the] CPAP system. The charge controller supplied with the systems could only support 5 panels for about 91 watts of power in peak sunlight. This expanded system worked great all this last winter.
After the success of my off-grid solar electric system, I now have a separate system for my ham radios, and am building a larger system to power our refrigerator.
It is quite possible and not that expensive to build an off-grid solar electric system to power relatively small loads like a CPAP machine. Like everything else in preparedness, it is better to build and try your preps now, while we still have the support infrastructure to allow you to make mistakes and correct them. - Suburban R.
JWR Replies: Many thanks for giving us the details on how you made your system work. Having separate system provides redundancy. And keeping them separate will help prevent an accidental deep discharge of your system. (This typically happens when an appliance is accidentally left turned on.) Having separate systems also gives you some redundancy because of equipment failure. You could fairly quickly reconfigure your ham radio power system into a power source for our CPAP. Something as simple as just a broken power cord could deadline a system, so buy spares for all of the crucial parts. Remember: "Two is one, and one is none!"
From what I have read, the motors inside most CPAP machines run on DC voltages. So for someone to run a DC to AC inverter, only to feed your machine's 120 VAC input jack (or cord) which is then in turn transformed back into DC is grossly inefficient. So I recommend this to anyone who is dependent upon motorized medical equipment (such as a CPAP machine or an Oxygen Concentrator) with an AC input: Do your very best to replace them with a unit that has a 12 VDC power input. If you contract with a medical supply company, or a care facility, or there is a medical insurance company involved, then this might be more complex. DO NOT overly complicate the process by telling them all about your alternative power system (or your plans to get one.) That will just confuse the situation. Simply tell them that you need a system that is compatible with power available from a car cigarette lighter. THAT is something simple they will be able to understand!