CPAP expected life span

markie wrote:Thanks for the input all. I too am skeptical on a unit 3 yrs past it's warranty. Keeping it for a backup or use in a RV is a good idea. Now that I'm retired I want to do some boondock camping and hiking. I never got the converter so trying to find one now seems impossible. Everywhere I check is "out of stock" or "discontinued item".

If I'm gonna be in the market for a new unit is there one that meets my needs of portability, quiet and good battery life? is there one that stands out above the rest that you recommend?
Markie

Markie,

Contrary to what someone else posted here, the S8 actually runs on 12VDC, not 24VDC like the S9 and A10.

To power the S8 from a 12V battery, you can buy any car DC adapter that can supply a regulated 12VDC (±1.5V) at 3.5A or more. Just make sure to cut the DC output plug off and install a new 2.5/5.5mm (inner/outer diameter) DC barrel plug wired with the center pin negative.

Regarding the output 12VDC specs, the actual required rating is 2.5A continuous with 1s 3.5A peaks at a 10% duty cycle (i.e. 1s at 3.5A, 10 s at 2.5A or below). I've suggested a 3.5A continuous spec to simplify but you can certainly use the tighter spec if that eases the selection of a suitable DC-DC converter.

In case you are wondering, no, I'm not making all this up. The specs above are from the official Resmed #33942 spec.

I own and use a Resmed #33942 DC-DC converter with my S8 Autoset II but I started out building my own adapter several years back.

If you are looking at upgrading your S8 and battery operation is important to you, note that the A10 has a higher power draw while the S9 has the lowest power draw of the three. See my post here: viewtopic.php?f=1&t=99843&p=943086#p943086 or check out the Resmed battery guide.

Finally, did you get my PM on your Li-Ion battery question?

Hope this helps.

Sgt Wilko

P.S. I tried inserting images to clarify things a little but it seems only web images can be inserted (i.e. via URL).

davecpap wrote:That 'brick' is the converter I was speaking of. It takes 12V input and supplies 24V to the CPAP machine. There is a loss involved in converting 12V to 24V -

a relatively well designed boost converter has an efficiency in the 95% range, so there is loss, but a fairly insignificant amount.

SgtWilko wrote:Contrary to what someone else posted here, the S8 actually runs on 12VDC, not 24VDC like the S9 and A10.

To power the S8 from a 12V battery, you can buy any car DC adapter that can supply a regulated 12VDC (±1.5V) at 3.5A or more. Just make sure to cut the DC output plug off and install a new 2.5/5.5mm (inner/outer diameter) DC barrel plug wired with the center pin negative.

I believe the S8 uses the same connector as many of the Respironics machines, but the opposite polarity.

You'll probably ruin the CPAP machine if you mix up the DC supplies.

Be really careful if you have Respironics and ResMed S8 in the same house.

The S8 humidifier does not run off of DC, it's AC powered. S9, A10, and PRS1 humidifiers draw their power from the blower unit and will run off of the DC plug or DC/DC converter that works the main unit.

my s8 just dies with about 6000 hours went to a a10 it's like night and day it's time to upgrade

k_ogre wrote:my s8 just dies with about 6000 hours went to a a10 it's like night and day it's time to upgrade

I also upgraded from an S8 Autoset II to an A10 after 5 yrs of daily usage with the S8. However, I can't say I saw a "night and day" difference in sleep or treatment quality. Perhaps because i was doing really well with the S8 already. The main improvement for me was the Climateline hose. My H4i humidifier had a hairline adjustment offset between desert dry and rainout... Perceived improvement from an upgrade will most likely be a case of individual situation and preference. Either way, it absolutely makes sense to upgrade given the S8's age and discontinued status. Keeping the S8 as a backup device is also a no-brainer.

In my case, the S8 is my go to unit when I'm out in the wild and need to run my APAP from battery power. The A10 form factor, integrated humidifier, and most importantly, higher power consumption (with humidifier OFF) all make it a poor choice for battery operation when camping/hunting/fishing/hiking etc. Yes, I know I can buy a cap to replace the A10 humidifier chamber but that does not make a significant difference for me given the other drawbacks I listed. If Markie is into outdoor activities and needs to run his xPAP from battery power, I think it is well worth the effort to find a Resmed DC-DC converter or build a homebrew DC-DC converter. He will benefit from the portability and longer run times.

Sgt Wilko

Wow, I can see why so many members comment positively on the assistance offered by other members of this forum. There sure is a collective knowledge and experience out there. Thanks so much to all who contribute.

SgtWilko - yes I got your PM on the battery guide link and your preference to purchase two C100's rather than one C222 for versatility of taking only what you need. That's a good idea.

I do have a question on the Resmed #33942. If its possible to use a car 12 volt adaptor as suggested with the plug polarity reversed what is the purpose of the #33942? Where is the need for a DC to DC converter for 12 volt to 12 volt conversion? Does the converter somehow limit the voltage the battery source can be drawn down to? What is it's purpose?

If anyone out there that may have a retired or broken S8, If you have a DC converter for sale please let me know.
Markie

markie wrote: I do have a question on the Resmed #33942. If its possible to use a car 12 volt adaptor as suggested with the plug polarity reversed what is the purpose of the #33942? Where is the need for a DC to DC converter for 12 volt to 12 volt conversion? Does the converter somehow limit the voltage the battery source can be drawn down to? What is it's purpose?
Markie

A 12 V battery is... not always at 12 V. Actual voltage will vary from full charge to depletion. I'll start by giving you a bit of simplified battery background then tell you what the DC-DC converter does. The details further below will hopefully make more sense to you that way.

The actual battery voltage will vary depending on battery type and state of charge but to over-simplify, lets say a range of 14V at 100% and 10V when depleted. Voltage will also vary with the amount of current you are drawing at any moment. A good part of that power draw induced variation will be due to the connection between the battery and the load. If you have a smart charger or maintainer connected to a lead-acid battery while using it to power your CPAP, voltage can be as high as 16V in certain modes and can pulse from 12V to 15V in other mode.

So... what does a #33942 DC-DC converter do that a simple adapter cable does not? It takes a varying 12V OR 24V battery input and provides a "steady" 12.0V output. It does that despite battery voltage variations above or below the nominal 12V. In technical terms, the #33942 is called a buck-boost converter. This particular model also does a few other things like galvanically isolate the xPAP from the battery, provide minimal surge suppression, overload protection, under-voltage lockout to avoid depleting a battery to the point of damaging it, over-voltage lockout, etc. Those are really just nice to have features but not essential in my mind unless you run the setup from a generator or while connected to a charger/maintainer. Furthermore, the under-voltage lockout feature accuracy is 10.5V ±1V so it will not really prevent you from hurting your battery since you could actually discharge it to 9.5V before that protection kicks in and that's too low.

That's why I suggested a car DC-DC converter (e.g. laptop or multi-voltage type) can be a very good substitute as long as you adjust the polarity of the DC barrel jack going to your S8. I've built and used one successfully many years ago before I lost it after a fishing trip.

Just to be clear, when I say a car DC-DC converter, I DO NOT mean a simple adapter cable. I mean an actual electronic circuit (a buck-boost converter similar to the Resmed #33942) which typically comes in the form of a brick with a cigarette lighter plug on one side (to the cig lighter socket) and DC barrel jack on the other (to the equipment being powered). Something similar to this DD90X coverter by Bixnet at 49.99$: http://www.bixnet.com/dd120xc.html.
IMPORTANT DISCLAIMER: I did not research the detailed specs and operation of this model and can not guarantee it will work with the S8.
I would personally prefer a device WITHOUT a voltage selector switch to avoid accidentally over/under supplying the S8 and potentially damaging it, but that is just a personal preference.

At first glance, the DD90X is rated at 90W (7.5A at 12V) which is plenty to power an S8. It also has good enough accuracy at 5% and reasonable efficiency at 88% (typical). On the nice to have side, it offers short circuit/overload protection on the output but no claimed over/under voltage lockout on the input.

That said, spec scrutiny would be required to determine the following for key S8 specific requirements:

• Is the rated output power dependent on the set output voltage?
  What is the maximum available continuous output current at 12V (needs to be 2.5A or more)?
  What is the maximum available peak output current at 12V (needs to be 3.5A or more at a 10% duty cycle. Only pertinent if the continuous available current is less than 3.5A)?
  What is the polarity of the DC barrel jack (it is most likely center pin positive but some models have a switch to reverse the polarity, others have adapter tips that do the same. Worst case, you cut it off and replace with a suitable tip wired with the right polarity for less than 1$)?
  Is the adapter a Buck-Boost type (Output voltage can be set higher OR lower than battery) or only a Buck type (output voltage has to be set lower or equal to battery)?

The info above can usually be found in the device spec sheet or by emailing/calling the manufacturer or supplier.

Hope this makes sense to you.

Sgt Wilko

SgtWilko,
I have to say you are thorough. I can't tell you how much I appreciate you taking the time to explain everything. I assume you're an Electronics Engineer by trade? If not you should be. Your response pretty much answers any question I had. Yes I understand the continuous current vs available peak current and the polarity importance. All I have to do now is get out the credit card and order. You sir have just solved my problem.
I hate to take anymore of your time but I'm curious on one last thing. If the DC to DC converters are 88% efficient how efficient is operating on a modified sine inverter for 120volt operation? I've used an inverter to power the S8 on an AGM battery but it only lasted the night. There was a significant drop in voltage by morning.

Thanks again Sgt.
Markie
P.S. I LOVE this forum

markie wrote: [...] I assume you're an Electronics Engineer by trade?

Yes. With obsessive compulsive tendencies to boot

markie wrote: [...] I hate to take anymore of your time but I'm curious on one last thing.

No worries. You can ask all you want.

markie wrote: [...] If the DC to DC converters are 88% efficient how efficient is operating on a modified sine inverter for 120volt operation? I've used an inverter to power the S8 on an AGM battery but it only lasted the night. There was a significant drop in voltage by morning.

OK. There is much more than just "one last thing" in that query. Lets break it down a bit...

First, the 88% typical efficiency I mentioned in my previous post was for the DD90X converter only. Other converters will have their own spec which may be higher or lower. Depends on the design. For comparison, the Resmed #33942 DC-12 converter is spec'd at 80% minimum efficiency (at rated load). Of course, when shopping for such a converter you want the highest efficiency possible. It is quite feasible today to get into the high 90s but given the fact that most of these vehicular DC-DC converters are designed and manufactured for minimum cost, high efficiency will be elusive unless you build your own.

Now about DC-AC inverters, the same logic applies re efficiency. Each inverter design will have its own efficiency spec which you can get from their spec sheet. These devices are inherently less efficient than DC-DC converters due to their innerworkings and design. "Pure" sinewave types are generally less efficient than modified sinewave types as they try to get closer to the ideal sinusoidal AC waveform. Furthermore, inverter efficiency will vary based on the type of load they are driving and the power level delivered to the load vs the inverter's rated power level. The closer the better. If you use a 1000W inverter to power a 20W load, your efficiency will be terrible. You need to size your inverter to have just enough headroom (say 20-25%) to have any hope of reasonable efficiency. You can ballpark general inverter efficiency at 50% but again, it will vary greatly. Bottom line, go for a DC-DC converter or direct battery connection (possible with Philips devices but not Resmed) if you can.

Finally, you mention your AGM battery voltage dropped "significantly" after just one night but you don't mention the battery capacity. It might just be that your AGM battery had insufficient capacity to start with, whether due to its size or state of charge. Note that once a 12V lead-acid battery reaches 10V, it has supplied all its available energy. You don't really want to discharge a lead acid battery (AGM or other) below 10V. Continuing to discharge it beyond that point will reduce its capacity quickly and permanently. That said, you should size your setup to avoid "significant" voltage drops. For example, if you have a 40Amp-H capacity 12V battery (roughly 480W-H), you can operate a 48W load for 10 hours before depleting the battery (i.e. reaching about 10V at the battery terminals). That same battery will last you 20 hours if you power a 24W load with it. These are the ideal theoretical numbers. Reality is usually not as nice and tidy because other factors come into play (inverter efficiency, rated power, operating point, ambient temperature, battery condition, quality/length of cables and connectors, etc).

I hope this long-winded response to your "one last thing" question is clear enough...

Here is another link you might find useful in your search for portable battery power for your CPAP: http://www.powerstream.com/home.html
I looked at them a few years back and found nothing interesting for me at that time but they seem to have broadened their offering since.

One last thing (which I wont elaborate on): if you or a friend are somewhat electronically skilled, you can find high efficiency DC-DC converter modules on Amazon and other online specialty shops that claim 95+% efficiency. However, these are typically "naked" PCB assemblies that you would have to package in a project box yourself. Can't really speak to the quality of these since I have not taken the plunge yet. I can say that they are basic (e.g. no input or output protection, so you will have to fuse and reverse polarity protect yourself) and dirt cheap. Here is an example of a board I was considering for building my own A10 converter (12V in - 24V out): http://www.amazon.ca/dp/B00KQH8ACW/ref= ... 1QV04X05OO
(my goto Canadian supplier want 170$ for the Resmed unit)


On that note, best of luck with your search.

Sgt Wilko

SgtWilko,

I was online looking at the basic DC-DC converter ckt boards you suggested as an alternative. To get the efficiency does come at a price as you mentioned. Using a bare bones ckt purchased for it's efficiency is the way to go if you're pursuing the max time in the woods on battery. For camping in the states using a home built unit wouldn't be a problem, at least for local camping, however, don't try to get on a plane. The airline frowns on homemade electronic boxes with wires coming out of them, they're funny that way. For that reason alone I will stick to a manufactured unit. I may look into this more in the future.
Thanks again for everything you offered it has been very helpful and interesting to read and learn. I'm sure others will benefit from this thread as well. I'll let you know how I make out in my travels.

Markie

I have an S8 with about 13,000 hours on it. It has been a work horse and has performed great. September 1 will be my 5 year anniversary with it (and on bipap therapy) and I may hang in there till then -- if it does! By the same token, I may want to upgrade sooner in case my S8 has a catastrophic failure. I want the S8 to remain functional so it can be my backup machine. I am going on vacation next week, so from what I have read, perhaps this trip will be it! I always carry the machine on the plane.

From what I have read, the differences between the S9 and the Aircurve (aka, 10) don't sound so big and if I get the S9 VPAP ST from Secondwind, I can get a new, open box one for a good price.

You may want to check out this thread - viewtopic.php?f=1&t=103170&st=0&sk=t&sd ... iking+cpap

The OP in that thread hooked up an S8 to a portable battery that's about the size of a kindle fire. I bought one for $120 and use it with my S9 for camping. Previously I used a Jumpstarter w/ my S8. I tried to make a DC converter and apparently got the polarity wrong - the s8 would no longer work , so be careful if you're rigging up your own adapter.

@SgtWilco,

Thinks for the info. That's better stuff than I've found anywhere, including Resmed.

I ordered this: http://www.ebay.com/itm/Universal-Noteb ... 1c38972b07

Quite a bit cheaper than than the Bixnet, but I think it'll work.

They sell this one on ebay: http://www.ebay.com/itm/ResMed-S8-12V-P ... 4af0edb4fe

It's just a Respironics 12v adapter with the cable end cut and reversed. It's got noise filters but no voltage regulation.



QUESTION: Do I wire the POSITIVE wire to the center of the power tip or to the outside of the tip? I think if I just clip the wire in two between the brick and the tip and reverse the wire, solder and shrink wrap I should be good to go, right?

Thanks, Ed

Laredo
I ordered this: http://www.ebay.com/itm/Universal-Noteb ... 1c38972b07

Quite a bit cheaper than than the Bixnet, but I think it'll work.

They sell this one on ebay: http://www.ebay.com/itm/ResMed-S8-12V-P ... 4af0edb4fe

It's just a Respironics 12v adapter with the cable end cut and reversed. It's got noise filters but no voltage regulation.



QUESTION: Do I wire the POSITIVE wire to the center of the power tip or to the outside of the tip? I think if I just clip the wire in two between the brick and the tip and reverse the wire, solder and shrink wrap I should be good to go, right?

Thanks, Ed

Ed,

I assume you have a Resmed S8. The 2.5mm barrel jack polarity is center-pin NEGATIVE, outer sleeve POSITIVE. I have an actual Resmed mechanical drawing for that plug so here are the specs:
Barrel O.D. : 5.5mm
Barrel Pin receptacle: 2.5 mm
Barrel length: 12.5 ± 0.3 mm
This is pretty much a standard 2.5 mm DC barrel plug which you can find at just about any electronics hobby/surplus store. Just pay attention to the barrel length since it does vary.

The device in the first ebay link looks OK but there is no polarity info provided so you will have to check it and correct yourself it if required.
To that effect, I would not cut the cord on the output side of the converter to reverse the polarity. I would buy a matching barrel jack along with a 2.5mm barrel plug (what the S8 requires for its DC input jack). Using these two connectors, I would wire a short polarity reversal "adapter which you can insert between the power converter output and S8. That short polarity reversal adapter will allow you some flexibility should you change power converters and most importantly, avoid frying your unit with a reversed power source.

Also, the power converter listing does not state if it is isolated or not when operating from DC. That's not a show stopper in my mind. What I am not crazy about is the output voltage selector switch. It makes it easy to fry your unit should the selector switch fail or simply move to a different voltage while it bounces around in your carry bag or when it is manipulated. Again, not a show stopper but, in my mind, the biggest risk of mishap for sure.

The device/cable in the second ebay link one looks like a "frankenkludge" which I would avoid.

DISCLAIMER: Info is provided based on my personal knowledge and experience. You assume all responsibility for any damage that may occur to your equipment by following any advice provided herein.

Regards,

Sgt Wilko