Thank you for the explanation. That makes more sense to me now. So, can I use any Resmed machine? It doesn't have to be one that's advertised as working off grid?ragtopcircus wrote: ↑Mon Oct 21, 2019 7:12 amRunning the humidifier takes a lot of power. To make the battery last longer, I use an inline Heat Moisture Exchanger. It has to be as close as possible to to your mouth and nose so it can capture moisture from your breath. An HME does not work as well as a regular humidifier, but it is better than nothing.
The Resmed DC-DC converter is what’s called a buck-boost converter. It transforms the voltage in (12 to 24) to a steady 24V (plus a lower level that Resmed also needs).
If we ignore efficiency for simplicity, Watts in = Watts out. Voltage x Current = Watts. That means that the DC-DC will only draw half as much current from a 24V battery (or two 12V batteries wired in series, or four 6V batteries wired in series.
I keep a supply of 6V lantern batteries for power outages because they last a long time on the shelf without needing to be kept on a charger.
Most batteries are more efficient when discharged slowly. You may be able to walk all day (even if your feet get sore), but most people tire quickly running up hill. Batteries work like that too. If you double the load current, you don’t just cut the usable time in half. You lose more than that, because the battery is less efficient at high current.
That means cutting the load current in half will usually increase the usable time by more than double.
I will need to go to all these posts and figure out what exactly I need to buy and then how to string it together. No doubt I'll have more questions then. But I wish there was more guidance for those of us who need the humidifier. I don't think the HME will work with either of my masks. The Dreamwear has a hose that comes out of the mask on top of the head and the Wisp has a pretty long mini-hose before it attaches to the main hose. So, I don't think either of those would qualify as being close to the mouth.
