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Battery system for ResMed S9 - have I got this right?
#1
Hi all

My wife's been recently diagnosed and she's using a ResMed S9. We're climbers and go away quite a lot so I need to find a solution for her to be away from mains power for a couple of nights at a time. I wouldn't anticipate being without the capability to recharge a battery for more than two nights.

I think what I'm proposing is going to work, but I'd just like someone who's ben here before to check it over for me before I spend a lot of money! I'm going to get her the ResMed 12v-24v convertor (part no 36970). Seems I can get this for £59+vat. Then I need a battery.

Her pressure is only 6cm H2O, and she'll do without her humidifier for a couple of nights, so the table in ResMed's pdf suggests I need 5Ah per 8-hour night. RS Components sell a 12Ah 12V lead-acid AGM battery for £24 (part no 537-7305). Add in a female cigarette lighter to bare wire adaptor and we're done for less than £100.

Two big questions, though. Firstly I recognise that I need a battery that is deep cycle. Is any AGM lead-acid battery automatically deep cycle? RS seem to let me specify AGM or deep cycle as the type. And will two nights use of this battery (probably using 60% of its capacity) run it too low, so I should be loking for a bit more capacity to avoid damaging the battery?

And will this charge off a regular mains car battery charger?

Thanks for any help!

Jamie
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#2
Welcome, Jaime.

I know very little about CPAP batteries for the S9. Did you try the search at the top of this page, looking for "S9 battery"?
INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. 
ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA.
INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINIONS ONLY AND NOT NECESSARILY STATEMENTS OF FACT.
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#3
If you have the option of an AGM battery, that seems like the better choice since it won't spill acid if the case is broken. I would think that any battery that could be used in a UPS (such as the one you specified) can handle deep discharge scenarios.

'Course, I don't have personal experience with any of this Smile
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#4
Hi Jamie,
WELCOME! to the forum.!
Hang in there for more suggestions and best of luck to you.
trish6hundred
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#5
ResMed says 11Ah per night for safety margin - this is at 6cmH2O with EPR off and no humidifier.

It's on page 14 here.

Other than just the chart on page 14, the rest of the linked document should help out as well. Marine battery will do, AGM is more expensive but should hold up better and can be turned upside down, etc.

Edit: Sorry, 11Ah for inverter - 5Ah for converter you mentioned getting. You probably already had the link to this pdf...

Look at the specs for the converter you are looking at, the one I ordered came with the Female DC to alligator clip connector all in the same ResMed box with the converter.

Also, forgot to answer that you can re-charge from mains power with a trickle charger, they are pretty cheap - around here good auto trickle chargers only run about $20.
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#6
Thanks for replies, all.

I've searched fairly extensively; most threads are about much larger battery systems (of the 50-100Ah range), either because the user needs a significantly higher pressure, or to run a humidifier, or wants to cover a longer time period. I don't see much discussion of such a small system.

Yep, that's the pdf I've been studying. I can't quite understand why anyone would go down the inverter rather than converter route, as the inverter costs more to buy and it's relative inefficiency means you need a bigger battery. Have I missed something?

Good to know the croc clip adaptor is in the box; that's saved me a purchase.

I just need to satisfy myself that their AGM batteries are safe to deeply discharge. It's the way they list AGM and Deep Cycle as options - you can get one or the other. Might have to give them a ring. I'll report back!

Thanks
Jamie
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#7
I have wired 12 volt into both my 4WD and my caravan while refurbishing it.
Your basic solution is good. I see no reason it will not work and matches my own plans using my caravan off grid with a 12V 100AH system I wired into it.
As the Resmed 12V power adapter comes with a built in fuse you do not need to put a fuse in the set up - if you plan to use it for anything else though a 20A fuse in the positive is strongly recommended. (could save the battery and stop a fire if you get a bad short). Honestly - if I was you I would get a few more AH and pick up a 12V led light strip for your trips as well- heaps of lumens at next to no AH (but you definitely have to fuse it then) - or if weight is an issue, a small foldable solar panel to charge it up each day.

With your charger you want at least a 3 stage charger - simple ones will not top the battery right up - they are designed to put enough charge into a cranking battery (one used to start a motor) which is then finished off with the car alternator. Spend the extra dollars and you will get a faster more complete charge.
I got a good 5 stage charger for a cheap price that also senses the type of battery that is connected and adjusts - now if the car battery does go flat I can recharge it too. about $30 from memory.

As I understand it AGM is a more expensive type of deep cycle battery which is why they call them out differently.

I also suggest you get a multimeter and learn how to use it to read the level of charge in the battery so you know you have enough power for the nights you are away - and to measure how much you are actually using.

If the link is allowed - (the link policy confuses me a little) This 4WD Camping site has extensive sub forum on 12v power and is worth a look http://www.myswag.org/index.php?board=9.0

Regarding the inverter - your comments are on the mark - highly inefficient so a larger battery - more cost etc, but it produces a more regular waveform that some machinery wants to ensure proper operation. honestly if Resmed did not make a 12V power supply it is the way I would go to ensure everything worked as it should (actually the 12v was critical in my buy decision - i would have bought the Devilbiss instead)

cheers
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#8
(09-12-2013, 02:46 AM)JamieWakeham Wrote: I just need to satisfy myself that their AGM batteries are safe to deeply discharge. It's the way they list AGM and Deep Cycle as options - you can get one or the other. Might have to give them a ring. I'll report back!

Thanks
Jamie

You are not going to kill the AGM in this kind of use. A lot of the AGMs out there are designed for and used in things like electric wheelchairs or kids' toy cars where they are charged, drained, charged, drained, etc. - they are meant to be charged and run down and recharged. Some full-sized AGM batteries, usually the bigger ones, are labeled "deep cycle" but for the most part, the tech is good for your anticipated application.

I have a small antique airplane that has no electrical system. I have been using a 10 AH 12v AGM battery as a portable power source for a portable GPS for many years with no problem. It powers it for several days of flying, then I just recharge it. It still holds a great charge. And the AGM batteries you are talking about are not that expensive, even if you were to wear it out in a couple of years.

I have three 35 AH AGMs for backup CPAP use - I figure that will give me about two weeks time on an Intellipap - the S9 on their power supply would go longer, maybe three weeks - but I don't have that part yet. For maintenance, I top off the battery charge every two months and have a 140W solar panel to charge them if the grid ever goes down hard for longer than a couple of weeks.

OMM
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#9
Thanks, both. I'm learning more about battery technology than I had anticipated...

I've decided on a 26Ah battery, which I can get for £36 - spare capacity seems like a good idea. I'll not need to run anything else off this - we're fairly seasoned mountaineers and have lighting all dealt with already! Comments about fusing the system if I do add anything later duly noted.

Charging seems to be my only remaining issue. If we're away for more than three or four nights without access to the mains, I *think* that if I hook this battery straight to my car's 12v socket, it'll at least begin to recharge, won't it? And couldn't overcharge because the car won't supply enough voltage to take it too far? This ought to be enough to keep topping it up if we do go away for longer?

For when we're back on the mains, I can buy a three-stage charger for £20 or so, but I'm a cheapskate and I'll avoid this if I can! I have a car battery charger that's quite old - I suspect it's effectively only one stage. Is there any reason I can't use this, and watch the voltage on the battery, and simply cut it off when it reaches 80% charge? I have so much spare capacity in the battery that I don't really need to take it to 100%. Or does not taking an AGM battery to 100% damage it, or shorten its life?
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#10
(09-12-2013, 05:50 AM)OMyMyOHellYes Wrote: You are not going to kill the AGM in this kind of use. A lot of the AGMs out there are designed for and used in things like electric wheelchairs or kids' toy cars where they are charged, drained, charged, drained, etc. - they are meant to be charged and run down and recharged. Some full-sized AGM batteries, usually the bigger ones, are labeled "deep cycle" but for the most part, the tech is good for your anticipated application.

Technically, AGM has nothing to do with "deep cycle." Most AGM batteries are deep cycle, but they do make a few AGM "starting" batteries and other non deep cycle types. You probably won't find any small AGM batteries that aren't deep cycle, though.

I believe the ResMed DC-DC converter will shut down as voltage drops to try to protect the battery.

Even a deep cycle AGM battery will be damaged if you run it down far enough and often enough, so don't abuse them by running them all the way down.
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