The adapter inefficiency should be low (especially since the S8 is a 12v machine) and its built into the Resmed figures.Finster63 wrote: I run the S8 at pressure level 9, and I need 1 night at a bare minimum - would prefer 2 or 3 (8 hours of sleep each night).
I was thinking that the DC 12 adaptor caused the inefficiency?
Amps and AmpHours are meaningless unless the voltage is stated. In this case, 32000 refers to the total milliAmpHours of the individual 3.7 volt Lithium Polymer cells. This totals 118 Watt-hours (volts X amps X hours), but then dividing by 12V you have something under 10 AmpHours. It get worse because some electronics have to somehow reconfigure the component cells to a useful voltage, and this voltage drops steadily as the battery discharges, so if you select 12V, you might only have 11v when its half discharged. Also, it seems the PowerAdd shuts down if the current draw is too high, and CPAP tend to draw a lot (2-4 Amps) when starting up, which may explain one report of needing to run two PowerAdds in parallel. I can't explain the one user report of 4 nights from a PowerAdd, but that user did say he uses a pressure of "6" and has only contributed several posts in one thread.Finster63 wrote: So if the S8 draws about 5 amp-hours per night, and the PowerAdd has 32 amp-hours (32,000mah), it should last 6+ days???
Not sure about the math on this.
Most electronics that have a built-in regulator will shut down at low voltage = usually around 10.5 to 11 Volts. So it seems unlikely that a CPAP would run it down to zero, but because LiFePO4 has a very flat discharge voltage curve, it will still be be above 3V/cell, or 12V for the battery at near 100% discharge. This may lead to some harsh language in the warranty. To be honest I've never had this type of battery, but I think we've all had experience cell phone or laptop or power tool batteries that at some point refuse to take a charge. So I would take claims like "1000 cycles" with a grain of salt and avoid spending too much on something that will die from abuse or obsolescence long before you can wear it out. If this issue is a major concern, get something like:Finster63 wrote: Based on your recommendation, I've started researching LiFePo4 batteries, but I ran into this review:
The review was for this battery:One problem with all Lithium batteries (as far as I have seen) is that they cannot be discharged too far or they will be not be rechargeable. I checked Battery Tender's warranty and if the battery is discharged below 8 volts it cannot be recharged and the warranty will not cover replacement. Most manufacturer's of conventional Lead-Acid, AGM and Gel batteries for similar applications will replace a discharged or dead battery that cannot be recharged if it is under warranty.
http://smile.amazon.com/Battery-Tender- ... dp_product
Would my CPAP discharge the battery below the 8 volts? or would it stop as soon as it went below 12v?
http://www.amazon.com/Watts-Meter-Analy ... 001B6N2WK/
so you can accurately track the battery performance.
As for the Battery Tender battery - I have been a big fan and promoter of the Battery Tender charger for many years. However, the marketing of the new line of batteries seems rather despicable to me. Instead of listing the actual AmpHours of the batteries, they post "lead acid equivalent" which presumably inflates their ratings by the 50% safety often used for traditional batteries. In the FAQs, they confuse the matter more with marketing gibberish about how their batteries might have 4.5 times the power. This is all nonsense since there are standard, meaningful ways to measure AmpHours and they are just trying to justify inflated prices with misleading specs. I would look for another vendor. (And I feel a nasty-gram to the manufacturer coming on ...)
I don't know why you think the Respironics is larger - the 560 and 460 pump measures 7" x 5.5" x 4" or 154 cubic inches and weighs 2.8 (although I just weighed mine at 2.3 lbs) while the Devilbiss is 4.2" x 6.5" x 6.9", or 188 cu in, and also weighs 2.8 pounds. Unless I've missed something, the Respironics is the clear winner.Finster63 wrote: I doubt that I would go with Respironics due to their larger size, but the DeVilbass IntelliPAP looks promising!
https://www.cpap.com/productpage/devilb ... ptions-tab