[Equipment] Battery power experience for Dreamstation Auto CPAP

[ozcedric]

just been trying my dreamstation auto with heated tube in an energy cost meter to see how much power it takes.
this is on a 240v supply.
the readings vary as the machine alters itself constantly (a-flex?), but all are at 5cmH as well.

with humidifier and tube
0.32A - 0.48A
power factor 66 (eg PF = 0.66)
44W - 56W

without humidifier and without heated tube
0.02A -0.06A
power factor 26 - 50
1.1W - 8.1W

readings seem correct using the formulae 'volts x amps x PF = Watts(real power)'

am i right in assuming a 90Wh battery will supply 8.1W for 11.11 hours (100% values applied of course)

the specs of phillips dreamstation battery kit says that it's 90W battery will last >14 hours at 10cmh without humidifier?
that seems very generous of them.

i'm just trying to get my head around the requirements for 1 sleep, whether it's a 22hr flight or 1 nights camping.

[OMyMyOHellYes]

What, exactly, are you using to measure current flow? Those numbers seem very, very low. Unrealistically low. But that is against 240V AC current too.

Kind of comparing apples to donuts?

I'm thinking you need to get down to where you can measure current draw between the power supply brick and the unit itself.

You can measure the current yourself at a little more granular level if you can put your hands on a multimeter that will record average DC amps. That may cost a little bit. But it's doable - since you are planning to use a battery anyway, I assume you have a battery cable? You would need a couple more "patch" cables with alligator clips. We could walk through that if you wish, or as a quick basis for comparison, I can share what I've learned.

I'm not nearly done yet, but across four different models and brands of CPAP/APAP (ResMed S8 Autoset II, S9 Autoset, PR System One 560 Auto, and a DeVillbiss Intellipap Auto), I am seeing a remarkably close average current draw between all machines of about 400-450 milliapmps at my estimated pressure of 11.5. For calculation of battery capacity required, we multiply that by 150% (batteries degrade over time due to a number of factors, so we throw in a 50% safety margin) so for calculation, we use .650 amps or 650 milliamps. That's without any heated humidification and a 95% pressure of around 11.5. Since your pressure of 5 cm H2O is less than that, I am assuming that you will use less power, just how much less, we don't know unless you really measure it at a granular level.

But if you were to take 650 milliamps as a benchmark, an 8 hour night would require a battery with a capacity of 5.2 amp hours capacity - so about a 65 watt hour rated battery (12 V * 5.2 AH) ... Another way to look at it would be to say making 14 hours would require a 9 AH battery multiply that by 12 V to get a battery with a watt hour capacity of 108. That is not far from what Respironics is telling you. And they have probably gotten a pretty good current draw number, so their number is probably bang on, maybe sandbagged a little.

OMMOHY

[OMyMyOHellYes]

Oh, and you said all your measurements were at 5 CM H20.  But you list an auto with a range between 5 and 20 CM?  Do yourself a favor and grab a free copy of Sleepyhead (look at the top of the forum page) and find your 95% pressure over a period of a few or several days. 

That is the pressure that you should be bench marking your power consumption off of.

OMMOHY

[ozcedric]

my last (and first) months average pressure was 5.59, with a 90% of 7.00

i am using an Arlec energy cost meter which displays amps, watts & power factor.

i do have some digital and analogue meters that i could use to conduct some other tests if you know any.

[OMyMyOHellYes]

My mistake.  It should be your average, and not the 95% pressure, you would want to pay attention to in these calculations if you have an auto machine and are looking at current references from a manufacturer.

I am not sure the wall plug meters are going to give you the granularity you need for this exercise.

You need to insert a digital multimeter that will record average amps so that the positive charge will flow THROUGH the meter when properly set to show amps.  As you observed, the current fluctuates several times per second so a visual reading will not do you much good.  That's why you have to get one that will record the average.  I don't know of any low priced meters ($20 USD/$25 AUD) that do that. The ones I've seen that will may start in the $70 USD/$85 AUD range.  But if you can get your hand on one, you would need to get it inserted between the power supply (hard to do) or a 12 V battery (pretty easy to do) and the CPAP/APAP.  Others have probably already done a better job explaining it online so you may want to google "Measure current or amperage with a multimeter" and find a good video.  One resource, though not a video, that I found near the top of the list that runs through the basics is:  https://www.electronics-notes.com/articl...urrent.php (note that this appears to be a non-profit educational/reference site that should meet list guidelines for links in this context).

Describing use of a specific meter is a little outside the scope of this post.  You may search for multimeter comparison videos over on the EEVblog hosted by an over caffienated Aussie named Dave Jones or there's a South African guy named Martin Lorton (MJLorton) that also has some good comparison videos.

OMMOHY

[NorthernGuy]

I was the original poster and now have 1 year (and almost 2 full summers) worth of experience feeding it on battery power.
One C-100 battery pack will power the Dreamstation for ~8 hours+ (no humidifier or heated tube obviously).  When I camp, I use 2 C-100 battery packs for 3 nights (hooking the 2 partially depleted packs together for the 3rd night)(that usually covers it, but not always the complete 3rd night).
I am using the special adapter from BPS for the Dreamstation - it is not a inverter but rather a power supply that provides the required special voltages/signals required by the Dreamstation. The picture looks like it has a fan, but it doesn't and it doesn't really get hot either, so I assume that it is pretty efficient.

A lead acid battery would be far cheaper, but would be impossible with the remoteness of my chosen campsites.


I am using the Philips Dreamstation AutoCPAP with a 90% pressure of 11-12 (according to the LCD screen).

Your experience may vary.

NorthernGuy

This does not constitute medical or technical advice - just my experiences.

[ozcedric]

hmmmm, secret signals twixt battery and DS.

from the BPS site
"While Respironics DreamStation series PAP devices operate from 12V direct current the DC input port on these devices require a proprietary signal in order to recognize a valid power source; therefore, a 12V power adapter is required to complete the connection between the device and the Freedom™ CPAP Battery"

i can see it's a great way to parallel 2 x batteries up, but i wonder what the proprietary signal is.
I've not seen that requirement or mentioned on any other battery suppliers equipment.
are they just talking about the correct polarity and correct size plug?

[NorthernGuy]

The proprietary DreamStation plug has been covered on here (see http://www.apneaboard.com/forums/Thread-...#pid164001 and http://www.apneaboard.com/forums/Thread-...#pid167070) in other threads and on other forums. The plug has 3 conductors - an outer-sleeve conductor, an inner-sleeve conductor, and a center pin, while most common DC plugs have only a center and outer conductor.

I am not sure of the actual signal, but it is not simply 12V DC.

[OMyMyOHellYes]

Uggh.

OMMOHY