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How much real autonomy time will my battery have with CPAP? A brief study
#1
How much real autonomy time will my battery have with CPAP? A brief study
Hello everyone,
This is the information from the study of the use of the Resmed Elite S9 CPAP with EPR and H5i humidifier with a 12-volt battery, AGM VRLA deep cycle and 35Ah in order to determine the autonomy time of a battery of said characteristics assuming extreme conditions in which during the days of use there is no available charging source, such as an AC-DC, DC-DC charger, photovoltaic cells (solar panels) and without resorting to the vehicle's starter battery or external sources charging as auxiliary batteries.
We avoid discharging the battery below 12.30 volts open circuit, to keep the battery at a voltage equivalent to 50% depth of discharge (DoD).
This study is empirical and therefore does not claim to be conclusive or exhaustive. The tests were done between midnight and 6am, over a period of 17 days, in an environment with a more or less constant temperature of 73°F (22.78°C) and with the voluntary participation of a real patient.

The study was divided into three phases:
Phase 1: CPAP with the humidifier off
Phase 2: CPAP with the humidifier on at level 4
Phase 3: CPAP with the humidifier at level 4 and the heating function on
These are the machine configuration options, which can be considered or discarded to the extent that they affect or not the energy consumption of the CPAP:

Set Pressure: 10.0
Max Ramp: 30 min.
Start Pressure: 4.0
EPR: Full time
EPR Level: 3
Mask: Full face
Tube: Standard
Climate Ctrl: Patient
Sleep Quality: On
Smart Start: Off
EPR Inhale: Med

Phase 1: CPAP with the humidifier off and Phase 2: CPAP with the humidifier on at level 4: Please see the attachment file, because I don't know how to copy here a table made in word
   
 
Phase 3: CPAP with the humidifier at level 4 and the heating function on: Please see the attachment file
   

During the three phases, as indicated by the clamp ammeter used, the consumption varied between 0.5 and 0.8 amps depending on the active CPAP function at each moment.
This study was limited to a single batch of tests and with the same, initially new battery, which was used for the first time in the so-called phase 1 of the study. The purpose is to give a general idea about the autonomy of a low-capacity battery with the typical consumption of a CPAP with the characteristics and configuration mentioned above, in the midst of hypothetical conditions of difficult access to a daily charging source. What motivated me to carry out this study was the difficulty that I had to find a similar analysis published on the internet, (I could not find it) that answered my question: How much real autonomy time will my battery have with the CPAP? On the ResMed page there is an article titled “ResMed Battery Guide” that I did not find very useful to understand the autonomy of a battery, because it only tells me that with a pressure of 10 cm H2O I need a 25 Ah battery for 8 hours, but it does not tell me what depth of discharge I will reach and how many days I will be able to use the battery before requiring a charge.

Before purchasing this battery, I consulted with two battery experts and they predicted that the battery charge would last a maximum of two days under these conditions. I could not believe that it was so little time and that is why I embarked on the adventure of buying the battery and carrying out this study.

Conclusions:
1. The study shows that with the humidifier on or off, but without using the heating function, the battery lasts basically the same time and decreases its charge to a value close to 50% after an average use of 2,040 minutes which is equivalent to 34 hours distributed over a period of 6 days, as observed in phases 1 and 2.
2. That with the humidifier on or off, but not using the heating function, the average voltage consumption is 0.22 per session
3. That with the humidifier at level 4 and the heating function on, the battery has an autonomy of 4 days reaching a safe voltage of 12.5 and that with an average consumption of 0.26 volts per session, the battery was not used for a fifth day to avoid dropping the voltage to 12.24 which is below the 12.30 set as the 50% safe depth of discharge for the battery.
4. That the minimum autonomy is 4 days, and the maximum is 6 days without subjecting the battery to a deep discharge and keeping the depth of discharge (DoD) below 50%.
5. That if this is the autonomy provided by a 35Ah capacity battery, if instead we use a 100Ah battery or more, the autonomy time will also increase in that proportion.

I hope that this study will be of some use to those who are curious about the possible autonomy of their battery in extreme conditions.
Any suggestion, correction or constructive criticism is welcome as it will be for the good of the entire community that makes up this forum.
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#2
RE: How much real autonomy time will my battery have with CPAP? A brief study
I may have missed this part, but how was your S9 connected to the battery?  Using an inverter?  DC/DC converter (12/24VDC)?  Or is the S9 a 12VDC machine?
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#3
RE: How much real autonomy time will my battery have with CPAP? A brief study
You are right, I omitted the detail of the connection that is made by means of an adapter of 12 volts in and 24 volts out, with a male connector for the cigarette case in the car and on the other side a connector that fits perfectly in the CPAP that By the way, it works with 24 volts. 
This adapter works at 3.75 amps and 90 watts. To the battery I adapted an aerial female cigarette holder connector because said battery is totally independent of the car's circuit.
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#4
RE: How much real autonomy time will my battery have with CPAP? A brief study
Thank you very much for your time, effort, and thoroughness in conducting your study. It should inform many forum members who are seeking a battery solution.

My question -- was that a real ResMed DC-DC Adapter for the S9?
"The object in life is not to be on the side of the majority, but to escape finding oneself in the ranks of the insane." -- Marcus Aurelius
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#5
RE: How much real autonomy time will my battery have with CPAP? A brief study
(07-20-2022, 09:42 PM)srlevine1 Wrote: Thank you very much for your time, effort, and thoroughness in conducting your study. It should inform many forum members who are seeking a battery solution.

My question -- was that a real ResMed DC-DC Adapter for the S9?

Thanks for your message. I know what it means to want to find information about something specific and not be able to find anything, it has always seemed very frustrating to me. In this way I wanted to contribute with my grain of sand.

The DC-DC adapter I use is generic, not ResMed branded, but it works perfectly and has a well-regulated voltage output. It cost me $32
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