(07-28-2017, 11:56 PM)heov Wrote: Get a UPS and it will work
But for only a VERY short time.
Let's compare head to head. NOT using any of my numbers. We will use only manufacturer OEM info. Let's use ResMed's published numbers using an S-9 AutoSet at a moderate, medium setting - pressure of 10 cm H2O with H5i humidifier set to 3 and no ClimateLine hose.
UPS = Battery + charger + inverter+ power fail switchover. For this analysis we assume the
APC BR1500G Back-UPS Pro 1500 VA ups (currently selling for around $170 USD from Amazon or Newegg). (Sidenote: manufacturer's online spec for that unit describes the wave form for that unit as "Stepped approximation to a sinewave" and NOT "a beautiful sine wave".)
To find what battery that UPS uses I went to
APC Battery and Upgrade Selector on APC's web site. The battery spec'ed is APC's RBC124 battery assembly. For a reality check I went to Amazon and found the replacement battery there too. While the specs don't explicitly cite the Ah capacity of that assembly, the the assemblies on both sites plainly show the assembly label. It is easier to see on Amazon, but both sites show the battery assembly plainly labeled "9Ah/12V".
At the heart of that big UPS is a relatively small 12V 9 Ah battery assembly. So there we have what we need to get going.
First, since we are talking about the UPS, which is essentially a battery and inverter in a box, we go to ResMed's
Battery Guide at
http://www.resmed.com/us/dam/documents/a...lo_eng.pdf . (on review, I note that link says "dam documents ...")
THE UPS UNIT
We go to the section for inverter use since that's what the UPS really is. For those following along, we're going to page 13. There we find the APAP unit will be expected to draw 3.01 amps of current running at the settings outlined above. Now, if we follow ResMed's assumption that rated Ah capacity is absolute best case scenario on the day that battery leaves the factory and is first fully charged, we have to allow a safety factor for ever growing age of the battery, number of recharge cycles, phase of the moon, how smelly the user's feet are, etc. etc. etc. ResMed uses a 50% safety factor. That means we multiply the expected current draw by 150%. For this illustration we use a current draw of 4.50 or (3.01 * 150%). For evaluation based on ResMed's assumptions, we calculate expected reliable run time thusly: 9 Ah / 4.50 A = 2.00 hours.
Two whole hours! To an extreme, if we take the very unlikely best case scenario with NO safety factor figured in we calculate the run time just so: 9 Ah / 3.01 A = 3.00 hours. So we expect probably two hours, maybe longer but never likely reaching three hours. Ouch. That's not much of a backup. ResMed says somebody would really need a 36 Ah battery for a whole night at those settings. That's why most knowledgeable folks just don't consider a home/office UPS to be a good choice for backup.
DIRECT DC BATTERY
Here, we're going to go back and just assume that the 32,000 mA battery worked. Or we can just as easily assume we have a 35 Ah AGM/SLA battery since they do reliably work and we're gonna do it both ways. Since we're not using that horribly inefficient inverter the UPS uses, we are going to the battery converter section of the book (ResMed began a nasty habit of requiring a proprietary converter to run it's units on DC power starting with the S-9. That is a downside if your have a ResMed unit. If you have a Respironics or DeVillbiss, consider yourself lucky.) Anyway, turn over in the Resmed
Battery Guide to page 18. Here we find the unit's expected current draw at our settings are 2.03 A (3.05 A with the 50% safety factor). So we work this two different ways - 32 Ah for the 32,000 mA battery and at 35 Ah for the AGM/SLA battery.
32,000 mA battery yields (32 Ah / 3.05 A = 10.49 hours) Ten and a half hours as opposed to two; if we assume magic batteries and take the safety factor out like we did above, this battery yields (32 Ah / 2.03 = 15.76 hours). Almost two eight hour nights. But given reliability issues, may not be a good option. Go on to the VERY reliable, but heavy 35 Ah battery mentioned as an alternative ...
The 35 Ah AGM/SLA battery yields (35 Ah / 3.05 A = 11.47 hours) About eleven and a half hours; if we go back into Never Never Land and assume a perfect battery on a perfect day in perfect condition, this battery yields (35 Ah / 2.03 A = 17.24 hours). Two nights of sleeping in late!
CONCLUSION
For the settings outlined above, we can have a two, maybe up to three hour battery backup if we buy the UPS that costs $170.
If we run our CPAP/APAP directly off the battery, we can safely get a night and a half of sleep, maybe two nights - cost $65 for AGM/SLAbattery, $25 for a small Deltran Battery Tender Figure $10 for a cigar lighter battery cable - $100 investment. Add $65 for the poor folks unfortunate enough to have a ResMed unit and have to get the proprietary 12/24 V DC converter. So total one time out of pocket costs are pretty much the same. Performance, on the other hand are greatly different with the direct DC solution the hands down winner.
Turn off the heat to the humidifier and we get much longer use (work the numbers in the book with no heated humidification).
Now if we want to talk about an efficient, effective UPS solution for CPAP/APAP/BiPAP use, I have a very elegant solution that I built from readily available components including a single 35 Ah battery. It keeps the battery charged and provides for automatic switch over/ switch back upon AC power failure/restoration. It costs more, but it is a really efficient, effective solution that will get me three and a half nights with heated humidification, and more eight or nine nights if I turn off humidification.
Sleep on it -
OMMOHY
