Using ResMed S9 and humidifier in my vehicle

Hello, I’m new to the forum.

For a few months, I’ve been using a ResMed S9 and H5i humidifier. Shortly, I plan to travel with my vehicle for at least three years, sleeping in it for several or many nights in succession (using accommodation just from time to time). Thus the matter of powering these two devices arises.

In the vehicle I use two starter batteries in parallel with a simple switch for connecting/separating them (i.e. no sophisticated split-charge system). The “accessories” battery is rated at 110 Ah. In the past, the system has worked well for running permanently an Engel 40-liter fridge, a 1000-W inverter sometimes, and a couple of auxiliary lights. Yes, I know that using one starter and one deep-cycle battery would be better but I’m not keen on changing the present arrangement, since starter and deep-cycle could not then be connected as at present.

I’m thinking of getting a ResMed 12 to 24 V converter, though am not yet certain about this. (I’ve read here that if power drawn is mostly for heating, an inverter is more efficient.) I’ve also read on the forum

viewtopic/t68248/Battery-backup-for-S9-AutoSet.html

that the S9 plus humidifier, run together in this way, might draw 3 amps per hour; another suggestion is 5 per hour. My 110 ah battery would thus provide between 36 and 22 hours of power (let’s say 22) but is this way of looking at the matter accurate? My understanding is that a battery should not be run down so far.

ResMed states somewhere that an S9 without humidifier draws (for a night’s sleep, I understand, namely 7-8 hours) 10-17 amps; with the humidifier, 31-80. This last figure, 80 amps, corresponds to 10 amps per hour, let’s say, which is twice as much as the higher estimate on the forum. I wonder why Resmed’s figures are so high. Are they being extremely cautious?

I’m trying to calculate, then, how many nights I could run the S9 and humidifier without recharging the 110 Ah battery. I’m considering a solar panel arrangement for replenishment. One such system would provide in theory input of 8.32 amps per hour. The other would provide 5.70 per hour.

I’d be grateful to receive advice about all of the above, some or all of which I don't understand well. Thank you.

ResMed states somewhere that an S9 without humidifier draws (for a night’s sleep, I understand, namely 7-8 hours) 10-17 amps; with the humidifier, 31-80.

I think it's possible those numbers from ResMed were referring to watts, not amps.
Watts is a measure of work or power consumption and is calculated by multiplying volts by amps.
Total power consumed over time is measured in watt-hours, or more commonly, kilowatt-hours.

I measured the power draw of my Resmed S9 Elite using a common consumer power meter:
http://p3international.com/products/p4400.html

This was with the Resmed 110V power brick. At idle, not blowing, the S9 consumed 3 - 5 watts.
(The numbers jump around because the power supply brick is probably a switch-mode power supply,
where the power being drawn varies and can appear to be different every time the monitor samples the power draw.)

When blowing at a constant 13cm, and the humidifier off, and no heated hose, the S9 draws 8-20 watts.
Notice that corresponds pretty well to the 10-17 number you mentioned.

When blowing at a constant 13 cm, and the humidifier set to 3, and no heated hose, the S9 draws from 12 - 60 watts.
That fits pretty well with the 31-80 number you mentioned.

So, for the sake of some calculations, let's say that when blowing, and the humidifier set to 3, its drawing around 36 Watts,
which is the average of the 12 - 60 that I saw. 36 watts would require 3 amps from a 12V battery, but the S9 requires 24V,
so you need to use an inverter with a12V battery to step the voltage up to 24V DC or to 110V AC.
Efficiency losses in the inverter might increase the draw to 4 amps from a 12V battery.
So, a fully charged battery rated at 110 Ampere-hours might give you around 25 hours, or 3 nights if you run it till it's dead,
which, as you said, is not good for batteries. Using such a battery for 2 nights would probably work well.

dcheddar: I don't have the battery or electrical knowledge to back-up or refute what you said, however the way you clearly laid out your premise was well done. Maybe someone will come along and comment on your conclusions. BTW, here's a recent huge thread on batteries for CPAP:
viewtopic.php?f=1&t=49115&st=0&sk=t&sd= ... tter+power

Hi, sorry to have been so long in replying. I’ve looked into this matter to some extent (have been reading and have spoken to the local ResMed suppliers).

I’d like to copy in a link but can’t seem to do it. Searching for “Resmed power consumption” should bring it up, though. It comes up at the top of my search list as “English-Battery Guide-Resmed”. It’s pdf format.

Resmed state that an S9 autoset (alone), with EPR setting 0, running via a suitable inverter (and factoring in a 50% safety margin) requires during an eight-hour period 11-18 amps (with treatment pressures varying from 6 to 20 cm H-2-0) Add an H5i humidifier (EPR setting 0; H5i set at 3), and the amp-range increases to 31-49.

Use instead the Resmed converter and the respctive amperages are 5-13 and 15-49.

Are these figures to be believed? Are Resmed stretching them in order to promote their converter?

QUOTE “ I think it's possible those numbers from ResMed were referring to watts, not amps.”

It seems they were in fact referring to amps.

I have a suitable inverter -which I need in any case for other things. (The S9 Auto will run on a 150-W, non-pure sine wave, state Resmed, and I’ve ordered a Resmed converter. I found one here in Germany for 99 Euros delivered, a bargain in these parts. (Supplied by Burbach & Goetz)

In my vehicle, I’m about to install in parallel a 115-Amp Banner leisure battery. My understanding of power consumption by the S9 Autoset + H5i is still somewhat hazy but getting better. I’ve been told by the Resmed suppliers that my S9 will “probably” operate at a treatment pressure of 8-10 cm H-2-0. (The device has been programmed/preset.) Anyway, using the 12-24V converter to run both the S9 and H5i, I’m estimating, on the basis of what I so far know, 20-25 amps per night. Does this seem reasonable or is my conclusion flawed?

Sounds like you have done your research. I recently was on a three week trip in my RV one week of which was "dry camping" with no power. I hooked my S9 up to a small inverter and ran it through the night with no problem. Of course my RV has large house batteries.

A simple and inexpensive way to answer your question is to get a Kill-A-Watt meter, http://www.amazon.com/P3-P4400-Electric ... B00009MDBU , and hook it up to your S9 for an overnight session. It will record the total KWHs used along with other data. On the plus side you can use it to track down other inefficient energy users in your home. Using the Kill-A-Watt will give you the actual energy used for your particular settings thereby answering your question in the most specific manner.

Bob