Battery question - check my math

[loggerhead12]

I'm starting to build my end-of-the-world battery system.

First step was to measure how much power my VAUTO uses. I've measured it for a couple of nights and will do a few more to zero in on an average. Last night, except for sleeping for nine and a half glorious hours it was a pretty typical night, with an AHI of 0.4. The system used 128 watt hours, so it was pretty close to 13.5 watts (128/9.5=13.47).

Most batteries you buy are measured in Amp Hours, which you have to convert to watt hours by multiplying by the voltage. My Resmed system uses a converter with an input of 12.6 volts and an output of 24 volts. So should I use 12.6 or 24 volts when doing the conversion to watt hours? My inclination is to use the 12.6 since that's what the battery will see.

Once I get this worked out I can buy or make any kind of battery for different situations.

[khauser]

To compute a battery's capacity in watt hours you'll multiply its amp hour capacity by its nominal voltage.

You did not say what you measured to come up with your system's usage. Was it the dc output of the wall plug? Was it the converter? And if so was that on the input or output side?

All converters have some loss, so where you measured it matters.

Also remember that per night usage can vary.

Ie, include some slop or realize it may not last the full treatment period.

[loggerhead12]

My measuring device is plugged in between the wall outlet and the power cord of the xPAP. The measured voltage was 122 volts. But that is really shouldn't matter, as it already measured the watt hours directly.

[khauser]

So that's the watt hour usage of the AC converter. Your machine would use less (converters have loss).
Unfortunately I don't know the relative efficiency of the ac converter vs the dc converter.

It's a good target to aim around though.

[edfreeman]

Resmed has a battery guide published to help with a battery and converter or inverter selection.

https://www.resmed.com/us/dam/documents ... lo_eng.pdf

[loggerhead12]

Thanks, I saw that. Unfortunately it doesn't have the Aircurve series. That's why I went with the direct measurement instead.

Sent from my Pixel 5 using Tapatalk

[Dog Slobber]

The AirCurve 10s uses the same hardware as the AirSense 10s. The published specs with regard to energy draw would be the same.