ResMed 12/24 volt DC Converter for S9 Series Machines
The ResMed DC Power Converter for S9 machines enables S9 Series CPAP Machines to be powered using a 12V or 24V power source such as those found in a car, boat, RV, or other battery. This converter also allows for use of the H5i humidifier and ClimateLine heated tubing with the S9 CPAP machines while on 12V or 24V DC power.
On my other CPAP machines, I have had a way to connect to 12-volt power in the case of a power outage. I'm just that kind of a guy - I want a backup for my backups... it's all about redundancy. I guess that philosophy came from when my dad was teaching my to fly an airplane (he was an instrument instructor). Systems in airplanes are designed to have several "layers" of redundancy - so that if one part of the system fails, you have at minimum one or two more parts that can perform the same function. After all, when you're flying at 120 knots 5,000 feet in the air, having a critical airplane part fail can ruin your whole day.
Likewise, I consider my CPAP machine to be a critical piece of equipment to my overall health. It's worth it to have redundancies built in to my therapy.
For my old "tank" CPAP (Respironics pre-2007 version of the REMstar Pro with C-Flex)... 12 volt backup was pretty simple - all I had to do was purchase a $25 12-volt DC power cord, attach it to the machine and hook it up to my cigarette-lighter connector with battery clips on the other end (already had purchased that for less than $20). The "old tank" REMstar Pro had 12-volt capability already built-in to the system... worked like a charm, and I only spent $45 for the necessary parts - having already purchased my 12-volt deep cycle "Marine" battery at WalMart for around $65.
As for my brand new, fancy super-duper ResMed S9 AutoSet machine - there is no built in 12-volt capability. There are basically two alternatives for operating the S9 on 12-volt battery power - first, is to purchase a quality AC-to-DC Power Inverter, with one end clipped to the battery, the other end to my CPAP AC power supply. While that type of a system should work fine, it's not a very efficient way to do it. You generally lose about 20-30 percent of your battery power as you convert from AC to DC current. I did't like that. Also, you're introducing yet another piece of equipment into the equation that has the potential to go bad (the Inverter). So, I patiently waited for ResMed to put their 12-volt Converter on the market. I waited... and waited... and waited... and finally, it came.
I paid about $95 (from Supplier #1 on our Suppliers List, where I do most all of my Sleep Apnea-related purchases) then bought a few CPAP filters to get the total over $100 (to qualify for free shipping). Other online suppliers were asking anywhere between $85-140 for this unit, but with varying shipping costs that ultimately raised the overall price, my deal worked out pretty good. Initially, when ResMed first announced these Converters, their suggested retail price was close to $150 or so. I was shocked at this high MSRP. Fortunately, my favorite online supplier did not offer them at the MSRP, but a more reasonable (but nonetheless expensive) price of $95.
Unpacking was simple. The directions were somewhat lacking, however. Small print and very basic, but enough to give basic information.
One caution: when you attach this DC Converter to your machine, make sure the small switch on the Converter is in the OFF position. That's a safety feature. It takes time for this Converter to power up - about 3-5 seconds before the green "okay" light comes on, signaling that there is now enough power to operate your S9 Machine. You don't want your expensive S9 unit to receive the inadequate lower voltages that will be coming out of the Converter during this 3-5 second power-up period. You need to give the Converter the required 3-5 seconds to "stabilize" first. Once the green light is ON, you can toggle the switch on the Converter, then turn on your CPAP machine.
Well, as I have said in previous posts, I have a very simple 12-volt solar power system that I installed at my house. Bought 3 of the 45-watt solar power kits from Harbor Freight, with a sale price and a 20% off coupon, only paid $129 or so for each kit (they retail for $250 normally). My system won't run the fridge or microwave or other high-amperage appliances, but it's super for basic home lighting, operating my 12-volt Ham Radio station and running my CPAP machine with ease. I now have two higher-end 6-volt Trojan T-105 deep cycle batteries attached to my system in series for storing 12-volt power. I also have about 50 feet of 12-volt wiring running from my back door (where the batteries are located) to my bedroom (where my CPAP is located).
Okay, so I'm not an electrician, although my dad was, and I had a very basic understanding of electrical theory. I should have known what would happen next. The first night when I plugged my precious S9 AutoSet into my brand-new 12-volt DC Converter, it seemed to work okay at first. Then it felt like I wasn't getting the "normal" amount of airflow. Then I would take a deep breath... and arrrrgh!!! The CPAP re-booted itself. Huh? Okay, it started up again and operated okay, but again, with that feeling of "not quite enough airflow". Hmm.... Operated okay for another 20 minutes... then I yawned in my bed and took in another very deep breath... REBOOT again!! Oh, geeze (I figured) I got a faulty Converter unit. Great. With some experimentation, I duplicated this re-booting thing 3 more times - each time I took a deep breath, the machine would re-start itself. So I plugged it back into standard 110-volt household power and went to sleep with the machine operating normally, this time with the normal amount of airflow and no re-boots.
In the morning, I remembered something that my dad had taught me - when you run Direct Current (DC) power over long distances of wire, you lose a heck of a lot of voltage due to heat dissipation in the wire itself, so by the time the voltage gets to the end of my 50-foot wire, I was losing nearly an entire amp of voltage. This power loss does not happen as severely with Alternating Current (AC), which is why our electrical grid power supply to homes is AC, not DC.
So, the following night, I decided to use one of my fully-charged 12 volt batteries - but this time bring the battery into the bedroom with me, and attach them directly to the ResMed S9 12-volt Converter... and.... YES! It worked flawlessly! My problem was that my long 50-foot run of wire was causing way too low of voltage at the other end. The shorter (3-foot) span of wire was the solution. I was relieved that I didn't have to return my Converter for a replacement unit. It was my fault, not the Converter's.
After the first night on 12-volt power, I was amazed at how little power my S9 (without the heated humidifier) actually used. My battery was reading 12.8 volts (open terminal voltage) at the beginning of the night, and when I woke up, it was still reading 12.8 volts. I figured that my S9 AutoSet was drawing an amazingly small 0.8 amps per hour. Wow, at that rate, if my figuring is correct, my two fully-charged Trojan 225-amp/hour deep cycles could run my CPAP machine (bringing the battery down to only an 80% charge without needing to be recharged) for well over 5 nights! Not bad. Maybe some of you electricians can tell me if my figuring is accurate or not.
Now, for those with heated humidifiers or the ClimateLine heated hose, I can't help you much on how long you can run your machine under battery power using this S9 converter... at least not until ResMed updates their documentation on running their CPAPs on battery power with the full specs and all... But I will say that (obviously) the higher you turn up the heat and humidity, the more 12-volt battery power you're going to use. And heating takes a LOT of battery power, several multiples of what your CPAP draws in power, so you may only get one or at most two nights of 12-volt power if you use the humidifier on the higher settings. Maybe our resident electricians can chime in with more detailed specs on this.
Overall, I am pleased with the ResMed 12/24 volt DC Converter for S9 units. The only reason I rated it 4 stars instead of 5 is because I'm not too pleased with the price. But still, at least I didn't pay the MSRP of $150.
Apnea Board Administrator