We have a trailer and sometimes camp without AC power supply. To do this with both my wife and myself using a ResMed CPAP, I had purchased a DC to DC converter for my wife's S9 machine and my AirSense 10 machine. I decided on a DC to DC converter instead of just using a DC to 115 volt inverter (which we have used) as the DC to DC converters are more energy efficient. When you camp off grid the amount of energy you use becomes an issue. We have two 6 volt golf cart batteries in our trailer which is quite a bit, but not so much when you start running two CPAPs each night. To help I have a 70 watt solar panel to help recharge the batteries each day, but it still is a bit marginal. I wish I had bought a 100 watt panel!! This has not gone perfectly as my wife found out with some distress that the ResMed DC to DC converter for the S9 has a design deficiency. With returns to the vendor I have tried three different ResMed converters for her machine with none of them working properly. If you shut off the heated hose and humidifier the converter works fine. But as soon as you turn these features on, the power supply trips out on overload. Surprisingly the converter I have for the A10 works fine even with the heated hose and humidifier turned on. The two power supplies look identical except for the connections to the machine. ResMed could not resist changing the power connection to make the S9 converter not work with the A10 machine. In any case we have made do with the defectively designed converter by turning off the extra features. This does help with power conservation also.
More recently my wife got a new AirSense 10 For Her and the S9 converter is not suitable for it due to the connection fitting. So I looked for a new converter and discovered that Amazon sells a knock off converter from China. It is much smaller, and cheaper. In Canadian dollars on Amazon.ca the ResMed converter is $125 while the knock off KFD unit is $65. The reviews were very favourable so I thought I would give it a try. Delivery was 2 days and it arrived today. My wife tried it out with an afternoon snooze in our trailer. It worked well with both the humidifier and heated hose turned on. See the SleepyHead chart below. Based on this test, I would suggest this is a good alternative to the ResMed converter. If we discover any issues I will try to remember to post again. My routine has been to leave this DC to DC converter in the trailer and I use it even when connected to the grid. My AC to DC converter stays at home so I don't have to bother to bring it.
The big difference between this knock off and the original ResMed converter is the size and weight. The knock off KFD unit is much smaller and lighter. I wondered if that would mean it is less efficient. Not a quantitative measure, but as it was used with fairly high power draw I found it got warm but not hot. I think it is probably just as efficient as the ResMed version.
Hope this may be of help to those looking for an off the grid solution to using a ResMed CPAP. I believe this company also makes converters for the S9, so it may be a good alternative to the defective design one sold by ResMed.
