(07-19-2016, 12:03 PM)MrGadget Wrote: I have an S8, not an S7, so my first question has already been confirmed previously about the center pin polarity. So I either need to buy one of the aftermarket DC adapters for the s8 $100 on ebay (because there are no original DC-12's available at any CPAP store, they all show discontinued) or just make one of my own, but I don't have access to the power filter part, and that may be critical.
I've used an S8 directly connected to a 12V battery, which works very well. The fully-charged voltage of over 14V goes fine, and it works well down to under 12V - I think around 11V but I can't remember exactly. More often I've used it with a cheap (circa $2 from Ebay from China, with XL4015 regulator chip) step-up adapter, which also works very well. The adapter is set to give output at 12V; if the input from the battery is less than this it will be stepped-up to 12V, if the battery is more fully charged and over 12V the regulator will just pass it through. The S8 is not fussy. The humidifier does not work on DC though, unfortunately.