Pilot-24 CPAP Battery System from Medistrom

[parkerdt]

My apologies Parker. You did indeed convert watt hours to amp hours. My bad for mis-reading.

Thanks! I try to do my homework, and post facts, best I can

Dave

[DSchabel]

Apparently you didn't read my thread closely:

If you have a 100 watt hour battery you divide by nominal voltage to get amp hours. 100 watt hours / 24 volts nominal = 4.167 amp hours.


If you don't believe this is the correct conversion from watt hours to amp hours, you can google it, which is what I did. Watts = Amps*Volts, so Amps = Watts/Volts. Unless you wish to reinvent Ohm's Law.


The ResMed site has battery tables for their machines. My AirSense 10
running with 8cmH20 pressure and the slim line hose needs a 10 amp hour battery to run for 8 hours.

So - 10/8 = 1.25 amp hour per hour of run time.

Thanks for the info Parkerdt.

That explains a lot. I think I will just stick to my 55 amp hour AGM battery and Battery Tender.

Jeff

The problem is Parkerdt simply divided the claimed watt-hour rating of the battery by 24 volts, to get 4 hours of operation, which is wrong unless the machine uses 1-amp of power. What we need are the operating amps at 24 volts of the CPAP, and humidifier if that is to be left on. The output of Pilot is 24 volts (a 12 volt version is available). Note the battery is not rated in amp-hours which would be much better.

I don't know how many amps the Resmed machines require during operation, but 1-amp at 24 volts is 24 watts per hour. So whatever amps are required to run the equipment is multiplied by the 24 volt to derive watts. The maximum operating time is the result of 100/24*amps. This is not a very powerful battery, and when pitted against the inefficient 24 watts of a Resmed machine isn't going to go very far, especially considering the battery will likely fail to power the device once it is depleted below 40%. So this 100 watt-hour rated battery probably only has a functional output of 60-70 watt-hours tops. Score a point for 12 volt machines.

This is incorrect. According to resmed data (see the ResMed Battery guide 198103/4 2015-08, on page 20), an AirSense 10 (with SlimLine tubing, as opposed to ClimateLineAir), at a setting of 8cm, will draw 0.79A at 12VDC, using a converter. This equates to 9.48W. Presumably the converter efficiency will have degraded this number, so it can be thought of as a more conservative number (most DC to DC converters have efficiencies in the 85% to 95% range - YMMV).

So, the Pilot-24's 98Whr spec means that it should power your CPAP for 10.3 hours (+5-15%).

[lawr1000]

This is incorrect. According to resmed data (see the ResMed Battery guide 198103/4 2015-08, on page 20), an AirSense 10 (with SlimLine tubing, as opposed to ClimateLineAir), at a setting of 8cm, will draw 0.79A at 12VDC, using a converter. This equates to 9.48W. Presumably the converter efficiency will have degraded this number, so it can be thought of as a more conservative number (most DC to DC converters have efficiencies in the 85% to 95% range - YMMV).

So, the Pilot-24's 98Whr spec means that it should power your CPAP for 10.3 hours (+5-15%).

DSchabel is correct.

I would add the "Presumably" is not needed. Since the AirSense 10 has a 24V input and the manual clearly shows current at 12V they "have" to use a converter and it just makes sense they used their 12V to 24V converter. So efficiency of their converter is already included in their current requirements.

Also if you use the ClimateLineAir hose with pressure at 8cmH20, humidity set to 8 and temperature set to 30C the current goes up to 4.77A at 12V or 57.2W. This would give you 1.7 hours with that battery.

[ED OF SO CAL]

I was wondering about this too. Thank you for the great information.

[OMyMyOHellYes]

't would be much simpler if they had just stayed with 12 V systems. And plain, coaxial barrel plugs for 12 V input. 2.1 or 2.5 mm. With GND on the outside terminal of the barrel, POS inside.

One standard. Like cell phone chargers where the regulators had to steer manufacturers to standard USB configurations and away from the silly proprietary plugs.

OMMOHY

[DSchabel]

't would be much simpler if they had just stayed with 12 V systems. And plain, coaxial barrel plugs for 12 V input. 2.1 or 2.5 mm. With GND on the outside terminal of the barrel, POS inside.

One standard. Like cell phone chargers where the regulators had to steer manufacturers to standard USB configurations and away from the silly proprietary plugs.

OMMOHY

Yes, and no.
Having a 12V input would mean that they required 12V fairly tightly regulated (unless they regulated internally).

This would preclude any easy 12V battery and/or vehicle conversion.
[technical]
Yes, you CAN use a flyback isolated converter, or a CUK converter or a buck-boost converter to take 12V +/-4V in and produce 12V, but these topologies are more complicated and/or (in general) less efficient (flyback is more complicated, needing a transformer, although not less efficient).
[/technical]

Using 24V means that they can design a converter to always boost voltage from 12V +/- quite a wide range.

[OMyMyOHellYes]

??????

12V CPAPs don't require "tightly regulated" 12 V supply.  They run just fine directly on 14 V (the power supply I have on mine is set to 14.1 V; the backup battery runs full from about 13.5 V).  They will run down to sub 12 V.  They simply don't require a constant, steady 12 volts.


OMMOHY